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Performance of a Ni/ZrO2 catalyst in the steam reforming of the volatiles derived from biomass pyrolysis
Abstract
The activity and stability of a Ni/ZrO2 catalyst have been studied in a continuous bench scale plant, in which biomass has been pyrolysed at 500 °C in a conical spouted bed reactor and the outlet volatile stream has been subjected to catalytic steam reforming at 600 °C in a fluidized bed reactor. The influence of space time has been analyzed, and both the fresh and the deactivated catalysts have been characterized by means of different techniques: N2 adsorption-desorption, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), temperature programmed oxidation (TPO), and transmission electron microscopy (TEM). The aim of this characterization is to relate catalyst performance to the evolution of the properties from the fresh to the deactivated catalysts. Thus, an increase in space time leads to an improvement in the stability of the catalyst extending its operation period from 20 to 100 min on stream, with a maximum H2 yield of 92.4% (referred to the maximum allowed by stoichiometry) when a space time of 20 gcat min gvolatiles⁻¹ has been used. Although the ZrO2 support has suitable properties, coke deposition is the main cause of catalyst deactivation.
... The results reported considerable increase in the conversion of oxygenated compounds into hydrocarbons with application of sulphided catalysts, as a high number of hydrocarbons was observed in the upgraded bio-oil [55]. The bio-oil obtained from thermochemical techniques could also be a suitable feedstock for steam reforming (SR) for production of H 2 or a mixture of CO and H 2 , called syngas [56][57][58][59][60][61]. H 2 produced from SR of bio-oil can be further used as a clean fuel, while syngas can be further subjected to Fischer-Tropsch process for production of hydrocarbons. ...
... The technique also requires highly active catalyst to enhance the conversion efficiency and hydrogen yield. Several studies have reported the application of various types for catalysts with promising results for hydrogen production [60,62]. ...
... However, it is believed that fixed-bed reactor is convenient to reform only lighter model compounds of bio-oil such as acetic acid and ethanol, while the reforming of larger model compounds or crude bio-oil leaves large amount of residue in the reactor and subsequent heating may lead to thermal degradation and formation of coke. Therefore, to reduce the coke formation during SR of bio-oil or larger bio-oil model compounds, fluidized bed reactor has been widely used and it is thought that the reforming process can be operated more efficiently than fixed bed reactor [56,59,60]. Where in fixed bed reactor a layer of coke can be easily formed, in fluidized bed reactor the circulated catalyst particles are in direct contact with bio-oil components and thus less coke formation and more hydrogen yield can be obtained. ...
Bio-oil produced from biomass pyrolysis and hydrothermal liquefaction is considered as the most sustainable alternative for depleting fossil fuels. However, the poor bio-oil properties, such as high viscosity, presence of solid particles, low calorific value and high instability are restricting its use as a drop-in fuel. The bio-oil properties can be significantly improved using different methods, such as catalytic upgrading, biomass pre-treatment and downstream bio-oil upgrading. This article focusses on the widely used methods for downstream bio-oil upgrading, such as hydrotreatment, solvent addition, emulsification, microfiltration and electrocatalytic hydrogenation. The bio-oil upgrading using non-polar solvents or preparing emulsions using surfactants have shown a significant increase in the calorific values and a considerable decrease in viscosity of the bio-oil. On the other hand, filtration of the bio-oil using membranes can remove the char particles and alkali and alkali earth metals from the bio-oil, consequently, leading to higher stability of the bio-oil. Electrocatalytic hydrogenation of the bio-oil has shown promising results to increase the content of hydrocarbons and increased pH by removing the carbonyl group-containing compounds from the bio-oil. The bio-oil can also be upgraded to other clean fuels, such as H2 using steam reforming approach, has been critically reviewed. Basic principles of the processes and effects of different parameters on bio-oil upgrading are thoroughly discussed. In addition, techno-economic analysis, policy analysis, challenges and future recommendations related to downstream processes are provided in the article. Overall, this review article provides critical information about downstream bio-oil upgrading and production of other high value-added fuels.
... The peaks at 250 °C to 550 °C, known as β oxygen, are ascribed to the desorption of the oxygen species nearby the vacancy sites. Desorption peaks at temperature higher than 550 °C, known as γ oxygen, are assigned to the release of bulk lattice oxygen [41][42][43]. The total number of O2 desorption of 10Ni/ZrO2, 10Ni-1ZrO2/Al2O3 (CI), 10Ni-10ZrO2/Al2O3 (CI), and 10Ni-10ZrO2/Al2O3 (SI) catalysts were 0.176, 0.297, 0.344, ...
... The peaks at 250 • C to 550 • C, known as β oxygen, are ascribed to the desorption of the oxygen species nearby the vacancy sites. Desorption peaks at temperature higher than 550 • C, known as γ oxygen, are assigned to the release of bulk lattice oxygen [41][42][43]. The total number of O 2 desorption of 10Ni/ZrO 2 , 10Ni- (Table 2), respectively. ...
The role of ZrO2 as different components in Ni-based catalysts for CO2 reforming of methane (CRM) has been investigated. The 10 wt.% Ni supported catalysts were prepared with ZrO2 as a support using a co-impregnation method. As a promoter (1 wt.% ZrO2) and a coactive component (10 wt.% ZrO2), the catalysts with ZrO2 were synthesized using a co-impregnation method. To evaluate the effect of the interaction, the Ni catalyst with ZrO2 as a coactive component was prepared by a sequential impregnation method. The results revealed that the activity, the selectivity, and the anti-coking ability of the catalyst depend upon the ZrO2 content, the Ni-ZrO2 interaction, basicity, and oxygen mobility of each catalyst resulting in different Ni dispersion and oxygen transfer pathway from ZrO2 to Ni. According to the characterization and catalytic activation results, the Ni catalyst with low ZrO2 content (as a promoter) presented highest selectivity toward CO owning to the high number of weak and moderate basic sites that enhance the CO2 activation-dissociation. The lowest activity (CH4 conversion ≈ 40% and CO2 conversion ≈ 39%) with the relatively high quantity of total coke formation (the weight loss of the spent catalyst in TGA curve ≈ 22%) of the Ni catalyst with ZrO2 as a support is ascribed to the lowest Ni dispersion due to the poor Ni-ZrO2 interaction and less oxygen transfer from ZrO2 to the deposited carbon on the Ni surface. The effect of a poor Ni-ZrO2 interaction on the catalytic activity was deducted by decreasing ZrO2 content to 10 wt.% (as a coactive component) and 1 wt.% (as a promoter). Although Ni catalysts with 1 wt.% and 10 wt.% ZrO2 provided similar oxygen mobility, the lack of oxygen transfer to coke during CRM process on the Ni surface was still indicated by the growth of carbon filament when the catalyst was prepared by co-impregnation method. When the catalyst was prepared by a sequential impregnation, the intimate interaction of Ni and ZrO2 for oxygen transfer was successfully developed through a ZrO2-Al2O3 composite. The interaction in this catalyst enhanced the catalytic activity (CH4 conversion ≈ 54% and CO2 conversion ≈ 50%) and the oxygen transport for carbon oxidation (the weight loss of the spent catalyst in TGA curve ≈ 7%) for CRM process. The Ni supported catalysts with ZrO2 as a promoter prepared by co-impregnation and with ZrO2 as a coactive component prepared by a sequential impregnation were tested in combined steam and CO2 reforming of methane (CSCRM). The results revealed that the ZrO2 promoter provided a greater carbon resistance (coke = 1.213 mmol·g−1) with the subtraction of CH4 and CO2 activities (CH4 conversion ≈ 28% and CO2 conversion ≈ %) due to the loss of active sites to the H2O activation-dissociation. Thus, the H2O activation-dissociation was promoted more efficiently on the basic sites than on the vacancy sites in CSCRM.
... The aim of the current study is to progress in the development of an original pyrolysis and in-line reforming technology by adopting the OSR strategy. This process has proven to have a great potential for hydrogen production from biomass under SR conditions, as it allows obtaining yields of around 10 wt% when the process is fine-tuned [27][28][29][30][31][32][33][34][35]. The authors have developed a combination of a conical spouted bed reactor (CSBR) for the pyrolysis step and a fluidized bed reactor (FBR) for the reforming one to perform pyrolysis-reforming in continuous regime. ...
... A scheme of this process is shown in Fig. 1. This dual reactor system has proven to perform well in the valorization of different biomasses, plastics and their mixtures [27,32,[36][37][38]. The use of a CSBR ensures operation under fast pyrolysis conditions with an efficient conversion of biomass into bio-oil [39,40], as well as a great flexibility for treating different biomasses and solid wastes and for process scaling up [41][42][43]. ...
The joint process of pyrolysis-steam reforming is a novel and promising strategy for hydrogen production from biomass; however, it is conditioned by the endothermicity of the reforming reaction and the fast catalyst deactivation. Oxygen addition may potentially overcome these limitations. A thermodynamic equilibrium approach using Gibbs free energy minimization method has been assumed for the evaluation of suitable conditions for the oxidative steam reforming (OSR) of biomass fast pyrolysis volatiles. The simulation has been carried out contemplating a wide range of reforming operating conditions, i.e., temperature (500–800 °C), steam/biomass (S/B) ratio (0–4) and equivalence ratio (ER) (0–0.2). It is to note that the simulation results under steam reforming (SR) conditions are consistent with those obtained by experiments. Temperatures between 600 and 700 °C, S/B ratios in the 2–3 range and ER values of around 0.12 are the optimum conditions for the OSR under autothermal reforming (ATR) conditions, as they allow attaining high hydrogen yields (10 wt% by mass unit of the biomass in the feed), which are only 12–15% lower than those obtained under SR conditions.
... In this system, solid biomass waste is pyrolyzed in a spouted bed reactor at a temperature between 500 C and 600 C [27]. According to past literature [28,29], a high performance solid waste pyrolysis reaction may yield up to 75% of bio-oil with remaining products of gas (mainly CO and CO 2 ) and char. Depending on the nature of the biomass, the molar ratio of chemical compounds of bio-oil mostly consists of oxygenated compounds such as acids (acetic acid, formic acids), alcohol (methanol, phenol), aldehydes, and acetone [25,30]. ...
... MgO were more active and stable over time as compared to Ni/ TiO 2 and Ni/SiO 2 catalysts. An additional study was reported by Santamaria et al. [29] for Ni/ZrO 2 on the influence of space time. As the coke deposition of this catalyst is primarily caused by the high concentrations of oxygenates, such effects can be minimized by manipulating the space time of the reactor. ...
Steam reforming of biomass pyrolysis oil or bio-oil derivatives is one of the attractive approaches for hydrogen production. The current research focused on the development of promising catalysts with favorable catalytic activity and high coke resistance. Noble metal such as Rh has been proven to achieve promising reforming reaction efficiencies. However, Ni has attracted considerable attention owing to its stability, cost effectiveness, and good activity in breaking C–C and C–H bonds. Nevertheless, Ni-based catalysts have serious carbon deposition problems arising from chemical poisoning, metal sintering, and poor metal dispersion. This paper attempted to review the current trends in catalyst development considering the aspects of supports, metals, and promoters as an effort to find possible solutions for the limitations of Ni-based catalysts. The present review also covered the current understanding on the reaction mechanisms as well as the future prospects in the field of steam reforming catalysts.
... It is to note that the H 2 production capacity of biomass by the strategy of pyrolysis-reforming is of the same order as that reported for bio-oil steam reforming, i. e., of around 10-11 wt % under optimum process conditions. [21][22][23][24][25][26] However, the technical development of the process is limited, as the vast majority of previous studies have been performed in batch mode in lab scale units. [13] The biomass derived product stream obtained by steam reforming is conditioned by two major limitations, as are process endothermicity and fast catalyst deactivation. ...
This study evaluates the potential of several biomasses differing in nature and composition for their valorization by pyrolysis and in line oxidative steam reforming. The first task involved the fast pyrolysis of the biomasses in a conical spouted bed reactor (CSBR) at 500 °C, in which product yields were analyzed in detail. Then, the oxidative steam reforming (OSR) of pyrolysis volatiles (gases and bio‐oil) was approached in a fluidized bed reactor (FBR). The reforming experiments were performed at 600 °C, with a steam/biomass (S/B) ratio of 3 and catalyst (Ni/Al2O3) space times of 7.5 and 20 gcat min gvol⁻¹. Concerning equivalence ratio (ER), a value of 0.12 was selected to ensure autothermal operation. Remarkable differences were observed in H2 production depending on the type of biomass. Thus, pine wood led to a H2 production of 9.3 wt %. The lower productions obtained with rice husk (7.7 wt %) and orange peel (5.5 wt %) are associated with their higher ash and fixed carbon content, respectively, which limit the efficiency of biomass conversion to bio‐oil. However, in the case of the microalgae, the poor performance observed is because of the lower conversion in the reforming step toward gases due to the composition of its pyrolysis volatile stream.
... Zirconia is a good active metal carrier because of its heat stability and unique properties, such as reduction-oxidation and acid-base characteristics [22][23][24][25][26]. Santamaria et al. [27] proved that ZrO 2 was suitable to support nickel because it produced limited coke with low-temperature carbon combustion. Supporting nickel catalyst over yttria-zirconia for DRM reduced the formation of carbonaceous deposits and lengthened the life span of the catalyst [7]. ...
The dry reforming of methane (DRM) was studied for seven hours at 800 °C and 42 L/(g·h) gas hourly space velocity over Ni-based catalysts, promoted with various amounts of gadolinium oxide (x = 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 wt.%) and supported on mesoporous yttrium-zirconium oxide (YZr). The best catalyst was found to have 4.0 wt.% of gadolinium, which resulted in ∼80% and ∼86% conversions of CH4 and CO2, respectively, and a mole ratio of ∼0.90 H2/CO. The addition of Gd2O3 shifted the diffraction peaks of the support to higher angles, indicating the incorporation of the promoter into the unit cell of the YZr support. The Gd2O3 promoter improved the catalyst basicity and the interaction of NiO with support, which were reflected in the coke resistance (6.0 wt.% carbon deposit on 5Ni+4Gd/YZr; 19.0 wt.% carbon deposit on 5Ni/YZr) and the stability of our catalysts. The Gd2O3 is believed to react with carbon dioxide to form oxycarbonate species and helps to gasify the surface of the catalysts. In addition, the Gd2O3 enhanced the activation of CH4 and its conversion on the metallic nickel sites.
... Thus, a decrease in valency is compensated by the formation of oxygen vacancies. 41 Khalesi et al. demonstrated that substitution of La with Sr in LaNi 0.3 Al 0.7 O 3 causes the organization of solid solution, enhanced porosity, and reduction of Ni +2 at higher reduction temperature (due to strong metal support interaction). The catalyst (with prior reduction) resulted in 80% H 2 yields at H 2 /CO > 1 at 750°C. ...
Finding a robust catalytic system for hydrogen production via dry reforming of methane (DRM) remains a challenge. Herein, MNi0.9Zr1−xYxO3 (M = Ce, La, and La0.6Ce0.4; x = 0.00, 0.05, 0.07, and 0.09) catalyst was prepared by the sol–gel method, tested for DRM and characterized by surface area and porosity, X‐ray diffraction, H2‐temperature programmed reduction, thermogravimetry, and transmission electron microscopy. In La0.6Ce0.4NiO3 catalyst, the substitution of Ni by 0.1% Zr results in a constant high catalytic activity (83% hydrogen yield at 800°C) due to the presence of reducible “NiO‐species interacted strongly with the support” (stable metallic Ni over reduced catalyst) and redox input by ceria phase for laying instant lattice oxygen during lag‐off period of CO2. Substitution of Ni by Zr and Y in the CeNiO3 catalyst system nurtures Ni3Y (providing highly stable metallic Ni for CH4 decomposition) and cerium yttrium oxide phases (providing strong redox input). CeNi0.9Zr0.01Y0.09O3 shows 85% H2 yield at 800°C.
... High conversion rates were achievable, regardless of the S/B ratio (3 is optimum), but higher space times are preferred for improving H 2 yield [82]. Using similar reactors in stage 1 and 2, Santamaria et al. [83] studied the performance of Ni/ZrO 2 catalyst for steam reforming of volatiles and obtained a H 2 yield of 92.4 %. However, the catalyst deactivates due to coke deposition within the first 100 min on stream. ...
Most hydrogen production technologies are dependent on non-renewable resources, which are not sustainable in the long run. However, H 2 can be produced in the future from renewable sources, becoming one of the cleanest energy carriers. Compared to other biomass treatment methods, the thermochemical pathways from biomass for sustainable H 2 generation offers a considerable promise for its industrial use. The most studied routes are biomass gasification and reformation of the bio-oil generated by biomass pyrolysis, while some works on su-percritical water gasification and bio-oil gasification are extensively developed to improve hydorgen production efficiency. This review discusses the most current developments in research on the methods of pyrolysis, gasification , steam reformation, and microwave-induced plasma for producing hydrogen from various types of biomasses, including lignocellulosic and woody biomasses. By utilizing the hydrogen produced from biomass, possibilities of creating a sustainable city were analyzed. There are many upgraded technologies to generate electricity using hydrogen produced from biomass such as gas turbines, combined cycle power plants, and fuel cells. The environmental feasibility of hydrogen usage was also evaluated, along with the status quo of hydrogen power plants in several countries. This review contributes to the large-scale implementation of hydrogen energy with in-depth discussion on the latest development.
... The final studies devoted to upgrading lignocellulosic biomass and the formation of H 2 -rich gas focus on the steam reformation of volatiles derived from the pyrolysis of lignocellulosic feedstock. Santamaria et al. [24,25] demonstrated that the whole process can be conducted in two steps. In the first study, a conical spouted bed reactor was used for the pyrolysis of biomass. ...
Due to limited fossil fuel reserves, the global political situation, and progressive environmental pollution, the development of new methods of hydrogen production is highly demanded [...]
... The weak basic sites correspond to Brønsted hydroxyl groups, moderate basic sites are associated with the Lewis acid-base pairing, and strong basic sites are attributed to low-coordination surface oxygen (O 2-) anions. The CO 2 adsorbed species are summarized in Table 4 accompanied by their structure [40]- [42]. The amount of each basic site was analyzed based on the peak area and the total amount of basic sites exhibit the CO 2 adsorption capacities concluding in Table 5. ...
Alumina (Al2O3) is widely used as a sorbent in CO2 adsorption and as a catalyst support in CO2 utilization. For this application, the CO2 adsorption ability is the most important property to be improved. Thus, this work presents the idea to modify the surface of a commercial alumina using an Mg-Zr mixed oxide. With this material, sites for CO2 adsorption can be created by generating oxygen mobility property simultaneously with the basicity. To prove this hypothesis, alumina modified with MgO, ZrO2, or Mg-Zr mixed oxide was prepared by an incipient wetness impregnation. The physicochemical properties of the bare alumina and the alumina modified with MgO, ZrO2, or Mg-Zr mixed oxide were investigated using N2 adsorption-desorption and X-ray diffraction. The achievement of oxygen mobility creation was quantitatively evaluated by O2-temperature programmed desorption measurement. The CO2 adsorption performance with the distribution of basic site strength was determined by CO2-temperature programmed desorption measurements. According to the results, the highest oxygen mobility was found in the alumina modified with Mg-Zr mixed oxide, which is approximately 1.7 times that of the bare alumina. The alumina modified with Mg-Zr mixed oxide showed the highest CO2 capacity by approximately 1.4 times compared to the alumina. It is because the cubic ZrO2 stabilized with MgO provided the number of oxygen vacancy sites that can be filled by oxygen atoms in adsorbed CO2 corresponding to the moderate and strong basic sites.
... Basically, zirconia is known to be a better support for active metal, due to heat stability and explicit characteristics such as acid-base and reduction-oxidation properties [16][17][18][19][20]. It has been proven that ZrO 2 is a proper support for Ni, as it gives restricted coke formation with a small carbon combustion temperature [21]. Yttrium oxide (Y 2 O 3 ) can either be acting as a promoter or support as a result of its unique chemical and thermal properties. ...
Methane Dry Reforming is one of the means of producing syngas. CeNi0.9Zr0.1O3 catalyst and its modification with yttrium were investigated for CO2 reforming of methane. The experiment was performed at 800 °C to examine the effect of yttrium loading on catalyst activity, stability, and H2/CO ratio. The catalyst activity increased with an increase in yttrium loading with CeNi0.9Zr0.01Y0.09O3 catalyst demonstrating the best activity with CH4 conversion >85% and CO2 conversion >90% while the stability increased with increases in zirconium loading. The specific surface area of samples ranged from 1–9 m2/g with a pore size of 12–29 nm. The samples all showed type IV isotherms. The XRD peaks confirmed the formation of a monoclinic phase of zirconium and the well-crystallized structure of the perovskite catalyst. The Temperature Program Reduction analysis (TPR) showed a peak at low-temperature region for the yttrium doped catalyst while the un-modified perovskite catalyst (CeNi0.9Zr0.1O3) showed a slight shift to a moderate temperature region in the TPR profile. The Thermogravimetric analysis (TGA) curve showed a weight loss step in the range of 500–700 °C, with CeNi0.9Zr0.1O3 having the least carbon with a weight loss of 20%.
... These differences in the pyrolysis volatile stream have an important impact on the subsequent catalytic steam reforming step. Continuous operation ensures fast biomass pyrolysis and the production of a volatile stream of stable composition 60,63,115,116 . In fact, higher H 2 yields have been reported under continuous operation 11 . ...
The growing environmental concerns associated with global warming along with the exponential rise in energy demand are boosting the production of clean energy. The combined process of biomass pyrolysis and in-line catalytic steam reforming is a promising alternative for the selective production of hydrogen from renewable sources. This Primer provides a general overview of the fundamental aspects that influence the hydrogen production potential of the process. Recent research studies and their main findings are highlighted. The current challenges and limitations of the process and ways to optimize the biomass-derived products of steam reforming are discussed. Finally, we evaluate progress toward the industrial scalability of the process. The combined process of biomass pyrolysis and in-line catalytic steam reforming is a promising alternative for the selective production of hydrogen from renewable sources. In this Primer, Lopez et al. outline the main factors influencing hydrogen production, from reactor configurations and operating conditions to product analysis and catalyst development.
... 37,38 Thus, although a wide range of base transition metals, such as Ni, Co, and Fe, and noble metals, such as Rh, Pt, Ir, and Ru, have been studied, Ni based catalysts are the most used ones because they strike a suitable balance between activity and cost. 39,40 In addition, different supports and their modification with promoters have also been widely analyzed. 12,41,42 An alternative and direct thermochemical conversion route for H 2 production from biomass and waste is the strategy based on pyrolysis and in-line reforming of the volatiles, which has several advantages in comparison with the aforementioned routes. ...
In recent decades, the production of H2 from biomass, waste plastics, and their mixtures has attracted increasing attention in the literature in order to overcome the environmental problems associated with global warming and CO2 emissions caused by conventional H2 production processes. In this regard, the strategy based on pyrolysis and in-line catalytic reforming allows for obtaining high H2 production from a wide variety of feedstocks. In addition, it provides several advantages compared to other thermochemical routes such as steam gasification, making it suitable for its further industrial implementation. This review analyzes the fundamental aspects involving the process of pyrolysis-reforming of biomass and waste plastics. However, the optimum design of transition metal based reforming catalysts is the bottleneck in the development of the process and final H2 production. Accordingly, this review focuses especially on the influence the catalytic materials (support, promoters, and active phase), synthesis methods, and pyrolysis-reforming conditions have on the process performance. The results reported in the literature for the steam reforming of the volatiles derived from biomass, plastic wastes, and biomass/plastics mixtures on different metal based catalysts have been compared and analyzed in terms of H2 production.
... Although the biomass gasification is conducted under optimized conditions, the produced tar together with syngas will result in fouling of downstream equipment after longtime operation [35][36][37][38]. In order to eliminate the biomass tar and realize efficient production of the H 2 -rich gas, many works of literature proved that the natural minerals [39][40][41]. ...
In the last few decades, the production of value-added chemicals from biomass has become a key research focus. Biomass gasification into syngas and further for methane, methanol, and C2+ alcohols production has already proved to be promising for utilization of renewable energy. Therefore, heterogeneous catalyst design and optimization are extremely significant for solving the issues of tar formation during biomass gasification. Apart from alkali metals, natural minerals, and synthetic catalysts, char and char supported catalysts prepared from residual biomass or coal have been already proved to be effective for tar reforming due to their relative chemical inertness, cheap price, excellent pore structures, etc. Advantageously, bio−/coal char could be modified and/or functionalized with heteroatoms doping and metal addition to improve activity in tar reforming. In this review, we systematically discussed the preparation, modification, and application of char catalysts in the reforming of biomass tar and tar model compounds. After that, we reviewed and compared the activity of char catalysts in tar reforming, and then we gave corresponding reactions and deactivation mechanisms over char catalysts in biomass tar reforming. Finally, we proposed existed challenges and shared our perspectives regarding future needs in char catalysts design for accelerating fuel sustainability and green development.
... Similar catalytic behavior of supported Ni catalysts in the pyrolysis of cellulose was previously presented by our group in [32,33]. Further measurements confirmed the increased stability of Ni/ZrO 2 catalysts [34]. Its redox properties and high oxygen storage capacity hindered the formation of coke deposits. ...
The pyrolysis of lignocellulosic biomass is one of the most promising methods of alternative fuels production. However, due to the low selectivity of this process, the quality of the obtained bio-oil is usually not satisfactory and does not allow for its direct use as an engine fuel. Therefore, there is a need to apply catalysts able to upgrade the composition of the mixture of pyrolysis products. Unfortunately, despite the increase in the efficiency of the thermal decomposition of biomass, the catalysts undergo relatively fast deactivation and their stability can be considered a bottleneck of efficient pyrolysis of lignocellulosic feedstock. Therefore, solving the problem of catalyst stability is extremely important. Taking that into account, we presented, in this review, the most important reasons for catalyst deactivation, including coke formation, sintering, hydrothermal instability, and catalyst poisoning. Moreover, we discussed the progress in the development of methods leading to an increase in the stability of the catalysts of lignocellulosic biomass pyrolysis and strengthening their resistance to deactivation.
... 3−5 Nevertheless, Ni based catalysts may suffer from sintering or coke deposition leading to their deactivation during biomass conversion. 6 That is why the role of the nickel support is extremely important. 7 It affects dispersion and stability of an active metal, mechanical and thermal resistance of the catalyst, its porous structure, and the number of acid or basic sites, among others. ...
The main goal of this work was to develop a highly active catalyst in lignocellulosic biomass conversion to hydrogen-rich gas. The studies were focused on the evaluation of an impact of dealumination of BEA zeolites on the catalytic performance of nickel-containing BEA zeolite catalysts in the investigated process. In order to increase an efficiency of hydrogen production, the effect of the catalyst preparation method was investigated (XRD, TEM, TPR, TPD-NH 3 , TG-DTA-MS and BET). During catalytic activity tests, cellulose and pinewood were initially pyrolyzed at 500°C. The formed vapors were subsequently upgraded by passing them through a catalyst bed at 700°C. The composition of the mixture of gaseous products was analyzed using GC-MS. The obtained results showed that Ni on dealuminated SiBEA zeolite, characterized by high number of vacant T atom sites, large surface area, high contribution of micropores, and relatively small pore size, was the most active among studied catalysts. The performed research demonstrated that increased reducibility of an active phase was beneficial for the enhancement of hydrogen production. The role of acid−base and redox sites as well as the influence of the state of Ni centers on the activity of Ni-containing dealuminated and nondealuminated BEA systems was also discussed. It is worth noticing that synthesized NiBEA zeolite catalysts, contrary to reference NiZSM-5 (possessing lower surface area and pore volume, lower reducibility and larger Ni crystallites), did not lose their activity in the conversion of lignocellulosic biomass in comparison to decomposition of pure cellulose.
... In a study conducted by Santamaria et al., Ni supported on ZrO 2 was used in the steam reforming of volatile components obtained from the pyrolysis of biomass. A maximum 10.73 wt% H 2 was produced, and they concluded that ZrO 2 is a suitable support for Ni, owing to its limited coke deposition, as well as its low coke combustion temperature [22]. A large part of the research using Ni on zirconia has shown that this catalyst suffers from deactivation as a result of the active metal sintering and carbon deposits. ...
Nickel catalysts supported on zirconium oxide and modified by various amounts of lanthanum with 10, 15, and 20 wt.% were synthesized for CO2 reforming of methane. The effect of La2O3 as a promoter on the stability of the catalyst, the amount of carbon formed, and the ratio of H2 to CO were investigated. In this study, we observed that promoting the catalyst with La2O3 enhanced catalyst activities. The conversions of the feed, i.e., methane and carbon dioxide, were in the order 10La2O3 > 15La2O3 > 20La2O3 > 0La2O3, with the highest conversions being about 60% and 70% for both CH4 and CO2 respectively. Brunauer–Emmett–Teller (BET) analysis showed that the surface area of the catalysts decreased slightly with increasing La2O3 doping. We observed that 10% La2O3 doping had the highest specific surface area (21.6 m2/g) and the least for the un-promoted sample. The higher surface areas of the promoted samples relative to the reference catalyst is an indication of the concentration of the metals at the mouths of the pores of the support. XRD analysis identified the different phases available, which ranged from NiO species to the monoclinic and tetragonal phases of ZrO2. Temperature programmed reduction (TPR) analysis showed that the addition of La2O3 lowered the activation temperature needed for the promoted catalysts. The structural changes in the morphology of the fresh catalyst were revealed by microscopic analysis. The elemental compositions of the catalyst, synthesized through energy dispersive X-ray analysis, were virtually the same as the calculated amount used for the synthesis. The thermogravimetric analysis (TGA) of spent catalysts showed that the La2O3 loading of 10 wt.% contributed to the gasification of carbon deposits and hence gave about 1% weight-loss after a reaction time of 7.5 h at 700 °C.
... The deoxygenation process is carried out through the stages of dehydration, decarboxylation, and decarbonylation. Several metal oxide catalysts, such as ZnO [6], MgO [7], CaO [7], ZrO2 [8], TiO2 [9], SiO2 [10], Al2O3 [11], and others have been studied to improve the quality of bio-oil through the catalytic pyrolysis process. The catalytic pyrolysis process is a promising method because it provides many advantages, including the absence of hydrogen consumption and the process conditions at atmospheric pressure. ...
In this study, an activated natural dolomite catalyst is used as catalyst for the palm empty fruit bunches (PEFB) pyrolysis to produce bio-oil. The research was conducted in fixed bed reactors operating in batches by varying several parameters, which are temperature (400-600°C) and nitrogen gas flow rate (100-300 mL.min ⁻¹ ). The results show that the catalytic pyrolysis process using an activated natural dolomite catalyst obtains a maximum liquid yield of 35.87% when using a 500°C catalytic pyrolysis temperature and the rate of nitrogen gas is 100 cm ³ /minute, while the yield of gas and solids is 53.12% and 11.76%, respectively. The use of the dolomite activation catalyst influences the product distribution of pyrolysis and the bio-oil chemical compounds.
... In order to improve the gas quality, some authors have proposed the integration of pyrolysis with reforming [27] or gasification [28] to reform the volatiles obtained during pyrolysis, therefore obtaining a H 2 -rich gas stream [27]. Nevertheless, these processes are more complex, since each one operates under different optimal conditions [29]. Thus, costs increase because of the need of more than one thermochemical unit [13,27,30]. ...
Thermochemical processes for biomass conversion are promising to produce renewable hydrogen-rich syngas. In the present study, model fitting methods were used to propose thermal degradation kinetics during catalytic and non-catalytic pyrolysis (in N2) and combustion (in synthetic air) of sugarcane residual biomass. Catalytic processes were performed over a Rh-Pt/CeO2-SiO2 catalyst and the models were proposed based on the Thermogravimetric (TG) analysis, TG coupled to Fourier Transformed Infrared Spectrometry (TG-FTIR) and TG coupled to mass spectrometry (TG-MS). Results showed three different degradation stages and a catalyst effect on product distribution. In pyrolysis, Rh-Pt/CeO2-SiO2 catalyst promoted reforming reactions which increased the presence of H2. Meanwhile, during catalytic combustion, oxidation of the carbon and hydrogen present in biomass favored the release of H2O, CO and CO2. Furthermore, the catalyst decreased the overall activation energies of pyrolysis and combustion from 120.9 and 154.9 kJ mol−1 to 107.0 and 138.0 kJ mol−1, respectively. Considering the positive effect of the Rh-Pt/CeO2-SiO2 catalyst during pyrolysis of sugarcane residual biomass, it could be considered as a potential catalyst to improve the thermal degradation of biomass for syngas production. Moreover, the proposed kinetic parameters are useful to design an appropriate thermochemical unit for H2-rich syngas production as a non-conventional energy technology.
... Additionally, suitable supports should be included to synthesize high-efficiency catalysts [23], as catalyst supports could not only disperse the active metal, but also participate in secondary reactions, thus that influence reaction activity and carbon deposition. Al 2 O 3 , ZrO 2 , CeO 2 , MgO, TiO 2 , SiO 2 , and dolomite [24][25][26][27][28][29][30][31] are among the most commonly studied catalyst supports in the literature, and exhibited good abilities to inhibit the rapid deactivation of Ni component. Interestingly, Ni/CeO 2 (75%)-ZrO 2 (25%) [32] catalyst is reported to have a superior performance in toluene steam reforming, owing to not only its great surface area, but also the high oxygen mobility and oxygen storage capacity of the support utilized. ...
... Previous studies by our research group compared five supports (Al 2 O 3 , SiO 2 , MgO, TiO 2 and ZrO 2 ) in the pyrolysis and in-line reforming of biomass in a conical spouted bed-fluidized bed reactor configuration, with the best results of hydrogen production and catalyst stability being obtained when Al 2 O 3 , MgO and ZrO 2 were used [49][50][51]. In order to improve catalyst's performance and stability, this study aimed at promoting the Ni/Al 2 O 3 catalyst with La 2 O 3 promoter. ...
The effect of La2O3 addition on a Ni/Al2O3 catalyst has been studied in the biomass pyrolysis and in-line catalytic steam reforming process. The results obtained using homemade catalysts (Ni/Al2O3 and Ni/La2O3-Al2O3) have been compared with those obtained using a commercial Ni reforming catalyst (G90LDP). The pyrolysis step has been performed in a conical spouted bed reactor at 500 °C and the reforming one in a fluidized bed reactor placed in-line at 600 °C, using a space time of 20 gcatalyst min gvolatiles⁻¹ and a steam/biomass ratio of 4. The Ni/La2O3-Al2O3 catalyst had a better performance and higher stability than G90LDP and Ni/Al2O3 catalysts, with conversion and H2 yield being higher than 97 and 90%, respectively, for more than 90 min on stream. Nevertheless, conversion and H2 yield decreased significantly with time on stream due to catalyst deactivation. Thus, the deactivated catalysts have been characterized by N2 adsorption-desorption, X-ray diffraction (XRD), temperature programmed oxidation (TPO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Coke deposition has been determined to be the main cause of catalyst deactivation, with the structure of the coke being fully amorphous in the three catalysts studied.
... ZrO 2 exhibits lower surface area in comparison to silica-based materials. However, it can interact with the active phase of the catalyst more strongly and exhibits a higher resistance against carbon deposition [28]. ...
The main objective of this work was to evaluate an impact of a support on the efficiency of nickel catalysts in the high-temperature conversion of lignocellulosic biomass to hydrogen-rich gas. The most important parameters influencing catalytic performance of the catalysts were identified. The properties of three materials (ZSM-5, ZrO2, and MCF (mesostructured cellular foam)) used as a support differing in surface acidity, surface area, pore structure, ability to interact with an active phase, and resistance to coking, have been studied. The results revealed that Ni/MCF, characterized by large pore size and pore volume, low acidity, small NiO crystallites size, and moderate interaction with the active phase, is the most efficient among studied catalysts, while an application of Ni on ZSM-5 support with high-acidity was not beneficial. The results suggest that structure of the support, in particular larger pore size and a better contact between an active phase and reaction intermediates, play an important role in the formation of gaseous products during thermal decomposition of lignocellulosic feedstock. On the other hand, high acidity of the support did not increase the formation of large amounts of hydrogen-rich gaseous products.
... Generally, the catalytic reforming of biomass pyrolysates has been used as a type of steam reforming to obtain high H 2 yields. Catalysts based on transition metals, such as Ni and Fe, have been widely studied owing to their low cost compared to those of noble metals [25][26][27][28]. Of all transition metals, Ni has been widely used as active phase for the steam reforming of oxygenates owing to its high H 2 selectivity [29,30] [31]. ...
This study aimed to determine the synergistic effects of CO 2 on the catalytic pyrolysis of pine sawdust over a Ni-based catalyst (Ni/SiO 2) to establish a sustainable platform for H 2 production. To elucidate the reaction mechanism , the CO 2-cofeeding pyrolysis of pine sawdust was performed. The CO 2-cofeeding pyrolysis of pine sawdust proved that the gas-phase reaction between CO 2 and pyrolysates led to the increase in the amount of generated CO. The CO 2 enhanced thermal cracking and dehydrogenation. These mechanistic features of CO 2 were catalytically enhanced when Ni/SiO 2 was employed as heterogeneous catalyst, which led to an increase in the amounts of generated H 2 and CO. Hence, the CO that was additionally generated during the gas-phase reaction of CO 2 and pyrolysates could be further converted into H 2. In addition, CO 2 could be looped in the CO 2-cofeeding pyrolysis of pine sawdust. Furthermore, exploiting CO 2 as raw material or reactive gas medium in the catalytic pyrolysis process also offered a strategic means for preventing coke formation.
The Ni/Al 2 O 3 structured catalyst shows stable performance for steam reforming of toluene and naphthalene mixture feeds for 50 hours under optimal conditions, exhibiting remarkable durability in steam reforming of model tar compounds.
Biomass gasifcation is one of the most viable approaches for exploiting biomass. It systemically employs several agents
in stimulating the desired reactions that lead to the conversion of biomass feed stocks to fuels/other products. Owing to
the biodiversity of the products of biomass gasifcation, they are fast becoming substitutes for fossil-based products/fuels.
In order to ensure optimal production of potential bioproducts, the process conditions of a gasifcation process have to be
essentially controlled within the ambience of high throughput. Based on existing literature, biomass gasifcation to fuels
is not essentially new; however, till date, none of the existing works seeks to unveil the role of heterogeneous catalysis in
biomass gasifcation toward ensuring high bioproducts yield. Heterogeneous catalysis seems to play a crucial role in biomass gasifcation owing to the fact that catalyst involvement in gasifcation processes helps to lower the activation energy
of specifc reactions; hence, under thermal infuence, the catalysts tend to hasten such reactions for the desired conversions.
Furthermore, it is also pertinent to take into consideration viable approaches for extending or maintaining the service life
of the catalyst employed by deploying apt modalities that abate catalyst poisoning (aging, deactivation and fouling); this
paper seeks to cover such challenges.
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The bio-oil obtained from thermochemical conversions of biomass (wood and agriculture waste, animal waste, solid waste etc.) can be an alternative to conventional liquid fossil fuels used in transportation or industrial sectors. However, bio-oil in its raw form is not of good quality as a fuel compared to conventional fossil derived fuels. In particular, bio-oil in its raw form has a low heating value, high oxygen and water contents, high viscosity and corrosive behavior. So, bio-oil needs to be upgraded for its direct use as a fuel. Meanwhile, the different kinds of valuable products can be derived from bio-oil: biofuels, biochemicals, and biopolymers when bio-oil is upgraded. The conversion of bio-oil into useful products has been the focus of numerous studies. Thus, it is crucial to study the research progress of this area to get the data needed to evaluate the viability of various processes for using bio-oil as feedstock in a comparative manner. Hence, this review article focuses on these value-added products and is twofold. The first fold explains the pyrolysis and hydrothermal liquefaction of biomass and compares the bio-oil properties obtained from both methods. Further, the second fold explains the key insights and respective state-of-the-art of generation techniques of value-added products from bio-oil in detail. In addition, value-added products from catalytic pyrolysis and their respective applications are also briefly discussed. Finally, the challenges and prospects of these techniques are presented. Based on this study, most of these technologies are still in the research and development (R&D) phase and cannot be scaled up due to technological limitations and cost intensive.
The main objective of these studies was development of competitive catalyst for the upgrading of biomass pyrolysis vapors to H2-rich gas. The performed experiments were devoted to determination of the effect of incorporation of zirconium into the structure of BEA zeolite on the performance of NiBEA in the mentioned process. Moreover, the most important parameters responsible for the increased activity of NiZrBEA catalyst in comparison to nickel supported on parent zeolite have been identified. The activity of synthesized catalysts was tested in two step fixed bed quartz reactor. Firstly, cellulose or pine were heated to the 500 °C in order to decompose lignocellulosic feedstock. Then, formed pyrolysis vapors were directed through catalyst bed (700 °C) where their upgrading took place. The obtained results revealed that an introduction of zirconium in the structure of BEA zeolite allowed for the increase in the efficiency of Ni catalyst in the formation of H2-rich gas. It was related to the increase in pore volume of the synthesized materials, formation of smaller nickel oxide crystallites and creation of the catalysts with moderate acidity.
Catalytic gasification of old corrugated containers with Fe-based catalysts is a promising way to produce renewable H2 along with the utilization of solid waste. In this study, the effect of support type and crystal form of support in Fe-based catalysts on the catalytic gasification of old corrugated containers was systematically investigated. The results show that, the introduction of Fe/γ-Al2O3, Fe/TiO2, Fe/SiO2, and Fe/ZSM5-30 promote H2 production. Among them, Fe/TiO2 has the highest catalytic activity on H2 yield (25.10 mmol/g) related to the formation of Fe2TiO5 solid-melt material. Fe/γ-Al2O3 shows the best H2 selectivity (46.34 %) and good H2 yield (24.19 mmol/g) due to good dispersity of Fe. Further, the order of catalytic effect on H2 selectivity is Fe/amorphous Al2O3 (51.46 %) > Fe/α-Al2O3 (46.98 %) > Fe/γ-Al2O3 (46.34 %). With the increase in cycle index, Fe/amorphous Al2O3 shows the best catalytic effect on H2 yield (25.56 mmol/g) after 11 indexes due to the formation of Al2FeO4. Fe/γ-Al2O3 shows the best stability on H2 selectivity (∼43 %) after 11 indexes.
Tar formation has become the bottleneck of biomass gasification due to it serious impacts the gas quality and device safety. Catalytic steam reforming (CSR) is a potential technology that can utilize tar to produce hydrogen. In this work, a series of NixFeyMn/ATP (x, y = 0, 0.1, 0.5, 1 wt.%) catalysts were successfully prepared by a sol-gel assisted impregnation method and applied to CSR of toluene, among which toluene was adopted as the biomass tar model. The characterization results of XRD, N2 adsorption-desorption, HRTEM, H2-TPR, NH3/CO2/O2-TPD and XPS demonstrated that the addition of trace of Fe and Mn promoted the uniform dispersion of active Ni metal and increased the reducibility and enhanced CO2 adsorption ability of Ni-based catalysts. Among them, Ni0.5Fe0.5Mn/ATP catalyst exhibited the highest toluene conversion (99.2%) and H2 yield (80.1%) and superior stability. This attributes to it has the highest Ni⁰/Ni²⁺ proportion and the cooperative effect of electron transfer among the Ni, Fe and Mn components. Additionally, the spent catalysts are characterized by HRTEM, XRD, TG-DTG and Raman. It confirms that trace of Fe and Mn doping improved the catalytic stability is ascribed to the inhibition of amorphous carbon and the growth of carbon nanotubes does not affect the availability of active sites.
The effect of catalytic reforming of volatiles from pyrolysis of walnut shell using an innovative catalyst was investigated in this study. The analysis was conducted in a two-stage fixed bed reactor operated at 700–1100 oC. The prepared Ni/olivine/La2O3/ZrO2 catalyst had a significant performance on the catalytic tar reforming reactions. In the catalytic reforming of tar, the weight of catalyst is critical. however, it was observed that the tar reforming efficiency increased with increase in catalyst-weight and temperature. In addition, the highest tar reforming efficiency (98.9%) was attained with 20 g of Ni/olivine/La2O3/ZrO2. After 4 cycles of regeneration, tar reforming efficiency was kept stable. The product gas composition was highest at 1100 oC, with a very low tar yield, which reduced from 18.1 – 2.1 wt.% at 700–1100 oC. At varying reforming conditions, the product gas composition increased. The product-gas distribution varied at different steam flow rates (3–9 mL/h) and particle size (0.2–3.5 mm) and the highest yield was achieved with the smallest particle size (0.2 mm) of walnut shell thus confirming the superb catalytic activity of Ni/olivine/La2O3/ZrO2 for tar reformation into gases owing to high dispersion of ZrO2 in the shells.
For CO2 reforming of tar, deactivation of catalysts caused by filamentous coke deposition limits its application in solid waste treatment. The filamentous coke removal can be aided by the lattice oxygen of active mental sites, however, there is no information on the influence of lattice oxygen in catalyst support on filamentous coke oxidation. To investigate the activity and resistance to coke deposition of different catalysts, based on a comparison of the performance of Ni/ZrO2, Ni/SiO2, Ni/MgO, and Ni/attapulgite catalysts, the influence of lattice oxygen on filamentary coke deposition is investigated in this study. In CO2 catalytic reforming experiments, the Ni/ZrO2 catalysts showed higher coke conversions (10%–23%) than the Ni/SiO2, Ni/MgO, and Ni/attapulgite catalysts. In the meantime, the lattice oxygen coverage of the Ni/ZrO2 superficies reaches 55.59%, giving Ni/ZrO2 a better resistance to filamentary coking. The high lattice oxygen coverage also improves the oxidation of the coke superficies by lattice oxygen. However, there was still 31.66% filamentary coke aggregation on the Ni/ZrO2 catalyst superficies. In conclusion, inhibiting the formation of filamentous coke and promoting the oxidation of filamentous coke are key to improving the efficiency of CO2 reforming of anaerobic tar. The results of the research can be used as a reference for the improvement of catalysts.
This work reports the development of a novel multifunctional catalyst by modifying the catalytic properties of red mud (RM) for the co-pyrolysis of biomass and polyethylene. This innovative catalyst design enables rearranging of the agglomerated phases in red mud, such as sodalite, into a new active and well-distributed structural framework (meso ZSM-5). The optimum hybrid catalyst (0.4-RM/ZSM) exhibits higher porosity (ten times more porous than the pristine RM), more accessible pores, and new weak basic sites compared to conventional red mud. In addition, it also shows higher catalytic activity than mesoporous ZSM-5 in promoting decarbonylation over dehydration. Hence, the hydrogen content of the produced oil over the hybrid catalyst (0.4-RM/ZSM) is 10.1 wt.% compared to 7.8 wt.% over the Meso-ZSM catalyst. Consequently, this increases the H/Ceff of the oil over 0.4-RM/ZSM to 1.28 compared to 0.9 over Meso-ZSM, making it a more compatible fuel.
A novel magnesium slag (MS) supported nickel-based catalysts (Ni/MS) was prepared and tested in catalytic reforming of volatiles derived from the pyrolysis of biomass components (cellulose, hemicellulose and lignin) and two biomass feedstocks (pine and straw). The physical and chemical properties of catalysts were characterized by XRD, TPR, BET, TEM, TPO-TGA and Raman spectroscopy. Ni/MS catalyst showed a higher tar removal efficiency than conventional Ni/γ-Al2O3 under the same Ni loading. The tar conversion of cellulose hemicellulose and lignin reached 94.8 %, 92.0 % and 89.4 %, respectively over Ni/MS catalyst. In addition, the lignin content of the biomass feedstock appreciably affected the yield and dew point of tar. The highest increment in gas and H2 yield (increased by 39.0 % and 106.4%, respectively) was observed in cellulose. The highest decrement in tar dew point (from 166.4 ℃ to 53.0 ℃) was observed in hemicellulose. The excellent tar removal of Ni/MS was attributed to the metallic Ni and Ni-Fe alloy on catalyst surface. Besides, the MgO and Fe2O3 phases in the support can retard the carbon deposition during the reaction. The results of this study are expected to provide insightful guidance for the application of Ni/MS catalysts for pyrolysis/gasification of biomass.
Pyrolysis is a research hotspot for realizing Chinese Herb residue (CHR) treatment and resource utilization, but there is little reported about in-situ no support catalytic pyrolysis of CHR. In this work, kinetics and no support catalytic pyrolysis characteristics of CHR were studied using a thermogravimetric analyzer and a fix-bed reactor system, respectively. Three groups: Ni-Fe, Ni-Cu and Ni-Co add into CHR and three kinetic methods: Coats-Redfern (CR) method, Flynn-Wall-Ozawa (FWO) method and Distributed Activation Energy Model(DAEM)use for calculate the activation energy, then analyses the gas, bio-oil and char of CHR pyrolysis. The results show that, catalysts can reduce the pyrolysis reaction activation energy. In FWO and DAEM model, the reaction activation energy will increase sharply if the conversion over 0.7. Compare with no catalyst group, add catalyst can restrain gas generation but good for oil production and char formation. Meanwhile, the surface of char is smoother than no catalyst. After test the char, we find that, metals of Ni, Fe, Cu and Co almost enrich in char, which may reuse as catalytic. This study may provide a feasible direction for the industrial application of CHR.
The characterization of coke, and its types, deposited on a Ni/La2O3-αAl2O3 catalyst used in the steam reforming of bio-oil has been studied by temperature programmed oxidation (TPO) coupled with different in-situ techniques: thermogravimetry (TG), modulated thermogravimetry (MTG), FTIR spectroscopy with mass spectrometry (MS), Raman spectroscopy, and differential scanning calorimetry (DSC). The steam reforming of bio-oil was carried out in a reactor equipment with two steps in series, comprising the bio-oil is thermal treatment (500 ºC) and subsequent reforming in a fluidized bed reactor (550-700 ºC; and steam-to-carbon ratio, 1.5-6). TG/MS-TPO experiments identify encapsulating and filamentous coke, and a more detailed analysis using other in-situ techniques enable to characterize the nature and location of 4 types of coke: (i) an encapsulating coke with aliphatic nature placed in the most superficial layers; (ii) an encapsulating coke with higher aromatic nature in inner layers; (iii) the most superficial layers of a filamentous coke, further from active sites and with a more carbonized structure compared to encapsulating coke; (iv) an innermost and mainly polyaromatic filamentous coke with a low oxygenates content.
The aim of the work was to investigate the influence of support on the catalytic performance of Ni catalysts for the glycerol steam reforming reaction. Nickel catalysts (8 wt. %) supported on Al2O3, ZrO2, SiO2 were prepared by the wet impregnation technique. The catalysts’ surface and bulk properties, at their calcined, reduced and used forms, were determined by ICP, BET, XRD, NH3-TPD, CO2-TPD, TPR, XPS, TEM, TPO, Raman, SEM techniques. The Ni/Si sample, even if it was less active for T<600 oC, produces more gaseous products and reveals higher H2 yield for the whole temperature range. Ni/Zr and Ni/Si catalysts facilitate the WGS reaction, producing a gas mixture with a high H2/CO molar ratio. Ni/Si after stability tests exhibits highest values for total (70%) and gaseous products (45%) glycerol conversion, YH2 (2.5), SH2 (80%), SCO2 (65%), H2/CO molar ratio (6.0) and lowest values for SCO (31%), SCH4 (3.1%), CO/CO2 molar ratio (0.48) among all samples. The contribution of the graphitized carbon formed on the catalysts follows the trend Ni/Si (ID/IG = 1.34) < Ni/Zr (ID/IG = 1.08) < Ni/Al (ID/IG = 0.88) and indicates that the fraction of different carbon types depends on the catalyst’s support nature. It is suggested that the type of carbon is rather more important than the amount of carbon deposited in determining stability. It is confirmed that the nature of the support affects mainly the catalytic performance of the active phase and that Ni/SiO2 can be considered as a promising catalyst for the glycerol steam reforming reaction.
Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.
This paper reports on the steam reforming, in continuous regime, of the aqueous fraction of bio-oil obtained by flash pyrolysis of lignocellulosic biomass (sawdust). The reaction system is provided with two steps in series: i) thermal step at 200 °C, for the pyrolytic lignin retention, and ii) reforming in-line of the treated bio-oil in a fluidized bed reactor, in the range 600–800 °C, with space-time between 0.10 and 0.45 gcatalyst h (gbio-oil)−1. The benefits of incorporating La2O3 to the Ni/α-Al2O3 catalyst on the kinetic behavior (bio-oil conversion, yield and selectivity of hydrogen) and deactivation were determined. The significant role of temperature in gasifying coke precursors was also analyzed. Complete conversion of bio-oil is achieved with the Ni/La2O3-αAl2O3 catalyst, at 700 °C and space-time of 0.22 gcatalyst h (gbio-oil)−1. The catalyst deactivation is low and the hydrogen yield and selectivity achieved are 96% and 70%, respectively.
H2 is regarded as one of the cleanest future energy carrier that can be generated from renewable sources and will give rise to a reduction of CO2 emissions and environmental problems related to the use of petroleum based feedstock. Thus, the thermochemical routes from biomass for sustainable H2 production compared to other biomass treatment routes have a great potential for its industrial implementation. Gasification of biomass and reforming of the bio-oil produced by biomass pyrolysis are the most researched pathways, although some studies dealing with supercritical water gasification and bio-oil gasification can also be found in the literature. Nevertheless, pyrolysis and in-line catalytic steam reforming strategy is gaining great attention due to its advantages compared to gasification and bio-oil reforming, especially those related to the optimization of each step (pyrolysis and catalytic steps) and bio-oil feeding. This review deals with the different reactor configurations, operating conditions and catalysts used in each process and compares the different alternatives in terms of H2 production, with emphasis placing on the advantages of the two-step strategy.
Fast pyrolysis is a promising thermochemical method of producing renewable fuels and chemicals from biomass and waste feedstocks. There is much interest in optimising the choice of feedstock pre-treatments, reaction conditions, reactor designs, and catalysts as well as product upgrading steps to improve the techno-economic feasibility of the process. This article summarizes the current state-of-art in thermal and catalytic fast pyrolysis and outlines the major considerations for process development. The status of process technologies and development efforts on thermal and catalytic fast pyrolysis are reviewed, with a focus on efforts producing bio-oil for use in manufacturing transport fuels or fuel blends as the final product.
The leading thermal pyrolysis processes, which use circulating, bubbling, auger screw and rotating cone reactor technologies, are reviewed alongside recent research and development activities on catalytic fast pyrolysis. This review finds that several technologies for thermal fast pyrolysis are operating at commercial scale, while integrated process development efforts are just starting to focus on applying catalytic fast pyrolysis at pilot scale. Processes for catalytic fast pyrolysis, either via in-situ or ex-situ upgrading of the bio-oil vapours is an area currently receiving significant research and development interest. This processing route may enable the production of partially upgraded bio-crudes which are suitable for processing to final fuel products in centralized bio-refineries or for co-processing in petroleum refineries. However, there remains a lot of fundamental and laboratory work to be done to develop deeper understanding of the processes, so that the catalysts and reaction conditions can be optimized.
New combinations of unit operations and possibly novel reactors will likely be required to economically convert biomass feedstocks into partially upgraded bio-crudes. Techno-economic assessment shows that bio-fuels from fast pyrolysis may be competitive with petroleum fuels in future, however there are currently only a handful of plants operating commercially.
The influence the support has on the performance of Ni catalysts used in the reforming of biomass fast pyrolysis volatiles has been assessed. Accordingly, five catalysts have been prepared by wet impregnation method, namely Ni/Al2O3, Ni/SiO2, Ni/MgO, Ni/TiO2 and Ni/ZrO2. These catalysts have been characterized by nitrogen adsorption/desorption, X-ray fluorescence spectroscopy, temperature programmed reduction and X-ray diffraction techniques. The pyrolysis-reforming runs have been performed in a bench scale unit operating in continuous regime. The biomass (pine wood sawdust) pyrolysis step has been carried out in a conical spouted bed reactor at 500 °C, with the volatiles produced (a mixture of gases and bio-oil) being reformed in-line on the prepared catalysts in a fluidized bed reactor at 600 °C. Remarkable differences have been observed amongst the catalyst prepared, with Ni/Al2O3, Ni/MgO and Ni/ZrO2 being those leading to the most encouraging results, whereas Ni/TiO2 and, especially Ni/SiO2, having a limited reforming activity. The performance of each catalyst has been related to its properties determined in the characterization.
The effect of reforming conditions (temperature, space time and steam/biomass ratio (S/B)) has been studied in the continuous biomass pyrolysis and in-line catalytic steam reforming process in order to establish suitable conditions for attenuating the deactivation of a commercial Ni catalyst by coke deposition. The experiments have been performed in a conical spouted bed and a fluidized bed reactor for the pyrolysis and reforming steps, respectively. Biomass fast pyrolysis was performed at 500 °C and the reforming operating conditions studied are as follows: 550–700 °C; space time, 10–30 gcat min gvolatiles⁻¹, and; S/B ratio, 2–5. The coke deposited on the catalyst has been analyzed by temperature programmed oxidation (TPO), and two types of coke have been identified, i.e., the coke deposited on the Ni active sites and the one separated from these sites, without filamentous coke being observed by transmission electron microscopy (TEM). Coke deposition has been related to the decomposition of the oxygenates derived from biomass pyrolysis and the re-polymerization of phenolic oxygenates. Suitable conditions to achieve almost full conversion with a H2 yield of up to 95% and stability for 160 min on stream, are as follows: 600 °C, space time of 30 gcat min gvolatiles⁻¹ and S/B ratio of 3.
A novel porous carbon catalyst was prepared by carbonization of D151 resin exchanged with nickel ion (Ni/RC). TEM images and XRD patterns manifest that nickel crystallite size (NCS) relies greatly on solution pH value and carbonization temperature. The as-prepared Ni/RC in pH 11 at 650 °C achieved the maximal specific surface area of 213 m²/g and metallic nickel particles are highly dispersed with a NCS of 5.7 nm. Ni/RC exhibited higher activity for corncob tar reforming than commercial Ni/Al2O3 and produced a gas yield of 46.8 mmol/g at 650 °C. The nickel particles growth above 650 °C causes the decline in catalytic activity of Ni/RC. In the presence of steam, a high tar-free gas of 84.5 mmol/g was obtained at 650 °C. This study sheds light on the possibility of Ni/RC as a promising candidate for H2-rich gas production from biomass under mild conditions.
The flash pyrolysis of waste truck-tyres was studied in a conical spouted bed reactor (CSBR) operating in continuous regime. The influence of temperature on product distribution was analysed in the 425–575 °C range. A detailed characterization of the pyrolysis products was carried out in order to assess their most feasible application. Moreover, special attention was paid to the sulphur distribution among the products. The analysis of gaseous products was carried out using a micro-GC and the tyre pyrolysis oil (TPO) by means of GC-FID using peak areas for quantification, with GC/MS for identification and elemental analysis. Finally, the char was subjected to elemental analysis and surface characterization. According to the results, 475 °C is an appropriate temperature for the pyrolysis of waste tyres, given that it ensures total devolatilisation of tyre rubber and a high TPO yield, 58.2 wt.%. Moreover, the quality of the oil is optimum at this temperature, especially in terms of high concentrations of valuable chemicals, such as limonene. An increase in temperature to 575 °C reduced the TPO yield to 53.9 wt.% and substantially changed its chemical composition by increasing the aromatic content. However, the quality of the recovered char was improved at high temperatures.
The continuous increase in the generation of waste plastics together with the need for developing more sustainable waste management policies have promoted a great research effort dealing with their valorization routes. In this review, the main thermochemical routes are analyzed for the valorization of waste polyolefins to produce chemicals and fuels. Amongst the different strategies, pyrolysis has received greater attention, but most studies are of preliminary character. Likewise, the studies pursuing the incorporation of waste plastics into refinery units (mainly fluid catalytic cracking and hydrocracking) have been carried out in batch laboratory-scale units. Other promising alternative to which great attention is being paid is the process based on two steps: pyrolysis and in-line intensification for olefin production by means of catalytic cracking or thermal cracking at high temperatures.
The recycling of N-containing plastics by pyrolysis or steam-reforming is typically complicated by the generation of toxic HCN. In this study, polyimide, as an example of an N-containing plastic, was gasified and the product gas was reformed over various Ni/Mg/Al catalysts. Effects of catalyst properties, steam, and temperature on the HCN removal and H2-rich syngas production were investigated. More than 99% HCN removal (compared with pyrolytic conditions) and ∼3000 mL g⁻¹ of H2-rich syngas with a H2/CO ratio of 10.4 were simultaneously achieved at 800 °C in the presence of a reduced-Ni1.0Mg3.6Al4.8 catalyst, then HCN was mainly converted into N2. On the other hand, non-reduced same catalyst enhanced hydrolysis of HCN into NH3 with more than 98% HCN removal at 800 °C, which is also a beneficial finding to recover useful NH3 from HCN, directly. Therefore, the present work achieved that the improvement of the H2-rich syngas yield and quality, and conversion of toxic HCN into non-toxic N2 or useful NH3 using the same catalyst, simultaneously.
Hydrogen production from polystyrene (PS) has been studied following continuous pyrolysis and in-line steam reforming. The first step was carried out at 500 °C in a conical spouted bed reactor and the subsequent reforming one was performed in a fluidized bed reactor on a commercial Ni catalyst at 700 °C. The effect space time and time on stream have on the reaction indexes (reforming conversion, yields of H2, CO2, CO, CH4 and hydrocarbons, and H2 production) has been determined. Furthermore, the process performance has been compared with the results obtained in a previous study conducted by feeding HDPE under the same conditions. Full reforming of PS derived volatiles and high H2 production of 29.1% were attained at zero time on stream. However, a significantly poorer performance of the catalyst was observed after 100 min continuous operation, with the decrease in activity being more acute than that observed for HDPE in a previous study. This deactivating behaviour has been related to the aromatic nature of PS thermal degradation products. The cokes deposited in the degradation of PS and HDPE have been analysed by means of temperature programmed oxidation (TPO) and electron microscopy, and the higher deactivation rate observed in the case of PS has been related to the condensed and encapsulating nature of the coke formed from aromatic hydrocarbons.
The reforming characteristics of biomass volatiles on anthracite chars were investigated by comparing the structural evolution of tars derived from cellulose and lignin as the major biomass components. In a two-stage quartz reactor, the pyrolysis volatiles of cellulose and lignin were produced in the first stage and then reformed in the second stage with or without the presence of anthracite chars between 600 and 900 °C. The results show that the presence of anthracite chars enhanced the destruction of volatiles of both feedstocks. Furthermore, the tar yields of lignin showed a slower decreasing trend with temperature than those of cellulose, suggesting that the lignin volatiles were more refractory to be reformed. The lignin tars had higher molecular weights and contained higher percentage of compounds with large aromatic ring systems (≥ 3 fused benzene rings) than cellulose tars in the studied temperature range. Compositional analysis revealed that tars of both feedstocks experienced the transition from phenolic compounds to polycyclic aromatic hydrocarbons with increasing temperature. The surface areas of anthracite chars were reduced because of coke deposition after interacting with the volatiles of both feedstocks below 800 °C, above which the net gasification of chars took place.
Catalytic steam reforming of n-hexane, 1-hexene, tetradecane and toluene over Ni a commercial catalyst has been carried out in a fluidized bed reactor at 700 °C. These compounds have been selected as model compounds of the volatiles formed in the pyrolysis of waste plastics in order to study in detail the performance of the catalyst in the pyrolysis-reforming of different plastic wastes. High carbon conversions and hydrogen yields are obtained at zero time on stream, with peak values being 96.5% and 82.8%, respectively, when n-hexane is used as model compound. Similar reactivity has been observed for tetradecane and 1-hexene, whereas lower carbon conversion (82%) and hydrogen yields (65%) are obtained for toluene. Concerning catalyst stability, olefinic compounds (1-hexene) and aromatic compounds (toluene) cause faster catalyst deactivation than paraffinic compounds (tetradecane and n-hexane). These disparities are explained by the different nature of the coke deposited and the different potential of the compounds to block Ni active sites, with olefins and aromatics being encapsulating coke precursors (amorphous and structured, respectively) and paraffins being filamentous and inert coke precursors.
Catalysts with active phase Ni, Co or Cu supported on γ- alumina were synthesized at constant loading (8 wt. %) and tested for the glycerol steam reforming reaction (GSR). The synthesized samples, at their calcined and/or their reduced form, were characterized by BET, ICP, XRD, DRS, NH3-TPD, CO2-TPD, TPR and SEM. The carbon deposited on their surface under reaction conditions was characterized by TEM, TPO, TGA and Raman.. Catalytic performance for the glycerol steam reforming reaction was studied in order to investigate the effects of reaction temperature on: (i) glycerol total conversion, (ii) glycerol conversion to gaseous products, (iii) hydrogen selectivity and yield, (iv) selectivity of carbonaceous gaseous products, (v) selectivity of liquid products and (vi) molar ratios of H2/CO and CO/CO2 in the gaseous products’ mixture. The stability of all catalysts was also investigated through time on stream experiments. It was concluded that catalytic performance, including liquid products’ distribution, depends on the acid-base properties of the materials. Specifically, a drastic drop in the activity of the Ni/Al catalyst was observed, while Co/Al and Cu/Al catalysts deactivate in a slower rate, confirming that coke deposition, associated with dehydration, cracking and polymerization reactions, takes place on the catalyst’s surface strong acid sites.
A continuous process has been developed consisting in the flash pyrolysis (500 °C) of high density polyethylene (HDPE) in a conical spouted bed reactor (CSBR) followed by steam reforming in a fluidized bed reactor (Ni commercial catalyst). The effect reforming temperature in the 600–700 °C range, space time from 2.1 to 20.8 gcat min gHDPE−1 and steam/plastic ratio between 3 and 5 have on product yields and gas composition has been studied. The continuous pyrolysis-reforming process performs well, with no operational problems and attaining complete HDPE conversion. Under the optimum conditions, i.e., 700 °C, space time 16.7 gcat min gHDPE−1 and steam/plastic of ratio 5, the H2 yield was 92.5% of that corresponding to stoichometry, which accounts for a H2 production of 38.1 g per 100 g of HDPE in the feed.
The continuous fast pyrolysis (500 ºC) of pine wood sawdust has been studied in a conical spouted bed reactor (CSBR) followed by in-line steam reforming of the pyrolysis vapours in a fluidized bed reactor on a Ni commercial catalyst. An analysis has been carried out on the effect reforming temperature in the 550-700 ºC range, space time from 2.5 to 30 gcat min gvolatiles-1 and steam/biomass ratio between 2 and 5 have on the pyrolysis volatile conversion, H2 yield and gaseous stream composition. The continuous pyrolysis-reforming process has shown great potential for H2 production from biomass, with no operational problems and allowing for full conversion of pyrolysis vapours. Thus, a maximum H2 yield of 117 g per kg of biomass was obtained at 600 ºC, at the highest space time studied (30 gcat min gvolatiles-1) and for a S/B ratio of 4. This yield is higher than those obtained by other alternatives, such as direct steam gasification or bio-oil reforming. Moreover, the char produced in the pyrolysis step has been continuously removed from the conical spouted bed reactor in order to be upgraded following promising valorisation alternatives.
In this study we examine the feasibility of steam reforming the mixed oxygenate aqueous fraction derived from fast pyrolysis bio-oils. Catalysts selective towards hydrogen formation and resistant to carbon formation utilizing feeds with relatively low steam-to-carbon (S/C) ratios are desired. Rh (5 wt%), Pt (5 wt%), Ru (5 wt%), Ir (5 wt%), Ni (15 wt%), and Co (15 wt%) metals supported on MgAl2O4 were evaluated for catalytic performance at 500 °C and 1 atm using a complex feed mixture comprising acids, polyols, cycloalkanes, and phenolic compounds. The Rh catalyst was found to be the most active and resistant to carbon formation. The Ni and Co catalysts were found to be more active than the other noble metal catalysts investigated (Pt, Ru, and Ir). However, Ni was found to form significantly more carbon (coke) on the catalyst surface than Co. Evaluating the effect of temperature on stability for the Rh catalyst we found that catalyst stability was best when operated at 500 °C as compared to the higher temperatures investigated (700 °C, 800 °C). When operating at 700 °C, significantly more graphitic carbon was observed on the spent catalyst surface. Operating at 800 °C resulted in significant carbon deposition, resulting in reactor plugging as a result of thermal decomposition of the reactants. Thus, a concept analogous to the petroleum industries' use of a pre-reformer, operated at approximately 500 °C for steam reforming of the heavier naphtha components, followed by a high temperature methane reformer operated in the 600–850 °C temperature range, could be applied in the case of steam reforming biomass derived oxygenates. Additional stability evaluations performed over the Rh, Ni, and Co catalysts at 500 °C and 1 atm, under similar initial conversions, reveal the Co catalyst to be the most stable and selective towards H2 production. However, deposition of carbon on the surface was observed. High resolution TEM on the spent catalysts revealed the formation of graphitic carbon on the Rh catalyst, and filamentous carbon formation on both the Ni and Co catalysts, albeit less pronounced on Co. Conversion and selectivity to CH4 over Co remained relatively stable at approximately 80% and 1.2%, respectively. By contrast, the Rh and Ni catalysts CH4 selectivity's were approximately 7–8%. The low selectivity to CH4 and enhanced resistance to coke formation suggests the Co catalyst may be a desirable economic alternative for the steam reforming of biomass-derived oxygenates compared to the more conventional Ni and Rh-type steam reforming catalysts.
Tar is unavoidable by-product during biomass gasification process. Catalytic steam reforming of tar to syngas is a promising way for the removal of tar from the gas products. However, the key issue for this way is catalyst development. To date, the developed catalysts always have advantages and disadvantages: nickel-based catalysts have high activity, but they are easily deactivated by coking; noble metal based catalysts have high catalytic activity, long-term stability and high carbon deposition resistance, but they are expensive; other transition metal catalysts such as Fe, Co and Cu exhibit a good performance, but they are also deactivated easily by carbon deposition in the case of high heavy-tar content in the tar; alkali metal catalysts also have high catalytic activity for tar reforming, but they are easy to be evaporated with the generated gases; natural catalysts have been widely applied for the steam reforming of tar due to its inexpensive, abundant and disposable, but their catalytic activities are lower than those man-made ones, and especially have low mechanical strength, making them not suitable to be used in fluidized bed reactor; zeolite is suggested to be a good catalyst support due to its high thermal/hydrothermal stability, high resistance to sulfur compounds, and easy to be regenerated; biomass char has been used as the catalyst or catalyst support in the steam reforming of tar due to its low cost and its natural production inside the biomass gasifier; even biomass ash now is considered to be a good catalyst for tar removal. In this review, to get better understanding of the mechanism of catalytic steam reforming of tar derived from biomass, tar formation, tar properties and catalytic reaction mechanism are also introduced, and prospects and challenges are summarized.
Abstract Metallic nickel (Ni0) nanoparticles could be in situ generated in the carbon matrix of rice husk char (RHC) via a facile one-step pyrolysis. The synthesized RHC Ni has a considerable performance on tar reforming. Tar reforming efficiency is increased with the increases of the used catalyst weight and reforming temperature. In particular, tar reforming efficiency can reach up to 90.5% and 99.8% by using 5 g and 10 g of RHC Ni, respectively. Tar reforming efficiency can also keep stable after 5 cycles. Besides, RHC Ni showed high tar conversion efficiency, increasing from 92.3% to 100%, when the reforming temperature was increased from 500 °C to 900 °C. RHC Ni showed a high catalytic activity even at the relatively lower temperatures. Furthermore, the yield of liquid products was decreased from 30.2% to 10.7%, corresponding to tar reforming. Accordingly, the gas yield was increased from 37.5% to 58.0%, in which the main components of syngas are CO and H2. It is noted that the PAHs compounds in tar could be significantly reduced by using the RHC Ni. The surface areas of the used RHC Ni were increased due to the char gasification rate higher than deposition rate. The RHC Ni has a high potential to be used for tar catalytic reforming.
Continuous pyrolysis of polystyrene has been studied in a conical spouted bed reactor with the main aim of enhancing styrene monomer recovery. Thermal degradation in a thermogravimetric analyser was conducted as a preliminary study in order to apply this information in the pyrolysis in the conical spouted bed reactor. The effects of temperature and gas flow rate in the conical spouted bed reactor on product yield and composition have been determined in the 450-600°C range by using a spouting velocity from 1.25 to 3.5 times the minimum one. Styrene yield is strongly influenced by both temperature and gas flow rate, with the maximum yield being 70.6wt% at 500°C and a gas velocity twice the minimum one.
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The best catalysts for promoting char gasification are Group I metals, particularly lithium and potassium, although other metals are active to a lesser extent. The most prevalent metal naturally in biomass char is potassium, which is not only inherently active, but volatilises to become finely distributed throughout the char mass. The formation of an active carbon/potassium complex is frequently proposed. Calcium is the other most common active metal found in biomass, but is far less effective and less volatile. In a gasification system the metals remain as carbonate due to the action of carbon dioxide. The alkali metals can react with silica to form silicates, which prevents catalytic action. Transition metals can also participate in catalysis of gasification; iron accelerates gasification and nickel prevents carbon deposition, which helps in conditioning biomass-derived syngas. Volatile iron pentacarbonyl has been identified as a promoter of the char gasification step, with catalytic activity related to the finely dispersed low-valency metal atoms generated during the thermo-decomposition of biomass.
Hydrogen and syngas from cellulose or cellulosic biomass gasification are environmentally clean gaseous fuels used for power generation. In this work, we explored the potential of several Ni/ZrO2 catalysts for the thermochemical conversion of cellulose to hydrogen. From the investigated catalysts the one consisting of tetragonal zirconia and containing the active phase with a small crystallite size and stable surface area, performed best in the cellulose conversion. Migration of zirconia on the nickel surface was found to be beneficial for catalytic performance. According to the XPS results, the highest Zr/Ni ratio was measured on the tetragonal phase of zirconia, followed by monoclinic ZrO2, with amorphous zirconia showing the lowest migration tendency.
Biomass gasification is one of the most important technologies for the conversion of biomass to electricity, fuels, and chemicals. The main obstacle preventing the commercial application of this technology is the presence of tar in the product gas. Catalytic reforming of tar appears a promising approach to remove tar and supported metal catalysts are among the most effective catalysts. Nevertheless, improvement of catalytic performances including activity, stability, resistance to coke deposition and aggregation of metal particles, as well as catalyst regenerability is greatly needed. This review focuses on the design and catalysis of supported metal catalysts for the removal of tar in the gasification of biomass. The recent development of metal catalysts including Rh, Ni, Co, and their alloys for steam reforming of biomass tar and tar model compounds is introduced. The role of metal species, support materials, promoters, and their interfaces is described.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Steam reforming (SR) and oxidative steam reforming (OSR) of furfural, 2-methylfuran, and guaiacol have been investigated in the temperature range 400-800 degrees C at a steam to carbon (S/C)-ratio of 5 and oxygen to carbon (O/C)-ratio of 0.2-1.4 over Ni/CeO2-K/MgAl2O4. Carbon oxides and H-2 were the major products in the SR of 2-methylfuran and furfural, while the by-products were methane, ethanol, 2-propanol, and acetone. Temperatures of 500 degrees C or above were needed to minimize the formation of by-products in the SR of 2-methylfuran and furfural. Phenolics, like benzenediols and phenol, were produced in high yields in the SR of guaiacol and temperatures of 780 degrees C were needed to totally convert guaiacol to carbon oxides and H-2. Carbon deposition was observed in the SR of all three model compounds and was most severe for guaiacol followed by furfural and 2-methylfuran. The carbon deposition could be reduced significantly by adding oxygen to the feed at a cost of a lower yield of H-2. Stable operation was observed initially (first 4 h) in the OSR of all compounds, but experiments over 24 h showed signs of deactivation due to an accelerated rate of carbon deposition in the SR of furfural and guaiacol. Furthermore sintering was more severe in OSR.
A Ni-Mg-Al-Ca catalyst was prepared by a co-precipitation method for hydrogen production from polymeric materials. The prepared catalyst was designed for both the steam cracking of hydrocarbons and for the in situ absorption of CO2 via enhancement of the water-gas shift reaction. The influence of Ca content in the catalyst and catalyst calcination temperature in relation to the pyrolysis-gasification of a wood sawdust/polypropylene mixture was investigated. The highest hydrogen yield of 39.6 mol H2/g Ni with H2/CO ratio of 1.90 was obtained in the presence of the Ca containing catalyst of molar ratio Ni:Mg:Al:Ca = 1:1:1:4, calcined at 500 °C. In addition, thermogravimetric and morphology analyses of the reacted catalysts revealed that Ca introduction into the Ni-Mg-Al catalyst prevented the deposition of filamentous carbon on the catalyst surface. Furthermore, all metals were well dispersed in the catalyst after the pyrolysis-gasification process with 20-30 nm of NiO sized particles observed after the gasification without significant aggregation.
The overall valorization of rice husk char obtained by flash pyrolysis in a conical spouted bed reactor (CSBR) has been studied in a two-step process. Thus, silica has been recovered in a first step and the remaining carbon material has been subjected to steam activation. The char samples used in this study have been obtained by continuous flash pyrolysis in a conical spouted bed reactor at 500°C. Extraction with Na2CO3 allows recovering 88% of the silica contained in the rice husk char. Activation of the silica-free rice husk char has been carried out in a fixed bed reactor at 800°C using steam as activating agent. The porous structure of the activated carbons produced includes a combination of micropores and mesopores, with a BET surface area of up to 1365m(2)g(-1) at the end of 15min.
Various Ni-Co bimetallic catalysts were prepared by incorporating sol-gel and wet impregnation methods. A laboratory-scale fixed-bed reactor was employed to investigate their effects on hydrogen production from steam reforming of bio-oil. The catalyst causes the condensation reaction of bio-oil, which generates coke and inhibits the formation of gas at temperatures of 250 °C and 350 °C. At 450 °C and above the transformation of bio-oil is initiated and gaseous products are generated. The catalyst also can promote the generation of H2 as well as the transformation of CO and CH4 and plays an active role in steam reforming of bio-oil or gaseous products from bio-oil pyrolysis. The developed 3Ni9Co/Ce-Zr-O catalyst achieved maximum hydrogen yield and lowest coke formation rate and provided a better stability than a commercial Ni-based catalyst.
Nickel catalysts supported on binary CeO2-ZrO2 carriers (28-100% CeO2 molar content) were prepared and evaluated regarding their catalytic performance for the CO2 reforming of CH4 (Dry Reforming of Methane, DRM). The textural and structural properties of catalysts and supports were studied in their calcined, reduced and used state by N2 adsorption-desorption, XRD, UV-vis DRS, TPR, SEM-EDS and TPH. Zirconium improves the textural properties of the CeO2-ZrO2 supports and the corresponding catalysts and enhances their textural stability under thermal reductive treatment. XRD analysis shows the formation of CexZr1-xO2 solid solution for all Ce/(Ce + Zr) ratios. Considerable alterations in the electronic environment of the cations and increased lattice defects in the binary solid solutions were detected by UV-vis DR spectroscopy. A significant increase in the reducibility of both supports and catalysts is observed in the presence of Zr. Compared to the zirconia-free sample, the Ni/CeO2-ZrO2 catalysts exhibited much higher activity for the title reaction, accredited to the increase of the surface concentration of the active sites. However, the amount of carbonaceous deposits is not straightforward related to the activity but depends on the Ce/Zr ratio. Among the zirconium containing catalysts, the zirconium-rich one exhibited the higher activity and the stronger resistance to the formation of carbonaceous deposits.
A study was carried out on the effect of temperature (in the 500-800 C range) and space-time (between 0.10 and 0.45 gcatalyst h(g bio-oil)- 1) on Ni/La2O3- αAl2O3 catalyst deactivation by coke deposition in the steam reforming of bio-oil aqueous fraction. The experiments were conducted in a two-step system, provided with a thermal step at 200 C for the pyrolytic lignin retention and an on-line step of catalytic reforming in fluidized bed reactor. Full bio-oil conversion and a hydrogen yield of around 95% (constant for 5 h) were achieved at 700 C, S/C (steam/carbon) ratio of 12 and space-time of 0.45 gcatalyst h(gbio-oil)- 1. The results of catalyst deactivation were explained by mechanisms of coke formation and evolution, which are established based on kinetic results and coke analysis by temperature programmed combustion. At 700 C the coke is gasified and Ni does not undergo sintering. The results of hydrogen yield were compared with those obtained in the literature using different reaction technologies.
Low-temperature catalytic reforming of volatiles and nitrogen compounds from sewage sludge (SS) pyrolysis was performed in a two-stage fixed-bed reactor over Ni/Al2O3 under inert and steam-reforming conditions. The results show that the reforming of SS volatiles significantly depended on temperature, space velocity, steam partial pressure, and feedstock type. Catalytic cracking of SS volatiles at 650 °C under inert atmosphere produced a tar-free synthetic gas with a H2/CO ratio of 2:1 in a high yield, which is preferred for maximum conversion efficiency for methanol synthesis. Steam as the gasifying agent gave a H2-rich gas (H2 content 68.0 vol.%) with a high yield of 82.5 mmol · g-1 (daf) at 650 °C, while the H2 yield is twice as that from non-steam gasification. Ni/Al2O3 effectively improved tar reforming and showed great resistance to coke deposition in the presence of steam. NH3, HCN, and nitrogen in tar are the main volatile nitrogen species in SS pyrolysis. Almost all the NOx precursors were converted to N2 by catalytic reforming at 650 °C both in the presence and absence of steam. Such an approach may lead to the development of a clean SS utilization technology and also H2/synthetic gas production technology from SS.
A novel process, which integrated with biomass pyrolysis, gas–solid simultaneous gasification and catalytic reforming processes, was utilized to produce hydrogen. The effects of gasification temperature and reforming temperature on hydrogen yield and carbon conversion efficiency were investigated. The results showed that both higher gasification temperature and reforming temperature led to higher hydrogen yield and carbon conversion efficiency. Compared with the two-stage pyrolysis-catalytic reforming process, hydrogen yield and carbon conversion efficiency were greatly increased from 43.58 to 75.96 g H2/kg biomass and 66.18%–82.20% in the integrated process.
We demonstrated an auto-thermal reforming process for producing hydrogen from biomass pyrolysis liquids. Using a noble metal catalyst (0.5% Pt/Al2O3 from BASF) at a methane-equivalent space velocity of around 2000 h−1, a reformer temperature of 800 °C–850 °C, a steam-to-carbon ratio of 2.8–4.0, and an oxygen-to-carbon ratio of 0.9–1.1, we produced 9–11 g of hydrogen per 100 g of fast pyrolysis bio-oil, which corresponds to 70%–83% of the stoichiometric potential. The elemental composition of bio-oil and the bio-oil carbon-to-gas conversion, which ranged from 70% to 89%, had the most significant impact on the yield of hydrogen. Because of incomplete volatility the remaining 11%–30% of bio-oil carbon formed deposits in the evaporator. Assuming the same process efficiency as that in the laboratory unit, the cost of hydrogen production in a 1500 kg/day plant was estimated at $4.26/kg with the feedstock, fast pyrolysis bio-oil, contributing 56.3% of the production cost.
Olivine and gamma-alumina have been used as primary catalysts for tar elimination in the continuous steam gasification of pine wood sawdust in a bench-scale plant provided with a conical spouted bed reactor. A comparison of the performance of each catalyst with that observed for a bed made up of inert silica sand shows that both catalysts have a significant activity for tar cracking/reforming, given that the amount of tar obtained by operating with beds of inert sand is reduced by 79% and 84% when olivine and -gamma-alumina are used, respectively. The tar cracking reduces selectively the content of light and heavy PAHs, giving way to an increase in the concentration of light aromatics. Furthermore, both catalysts cause a positive effect on the gas composition by slightly enhancing the water-gas shift and reforming reactions.
High density polyethylene (HDPE) cracking has been carried out in a thermal-catalytic two-step unit for the selective production of light olefins. Continuous pyrolysis of HDPE has been conducted in a conical spouted bed reactor at 500 °C, and the volatiles formed (mainly waxes) have been transformed in a downstream fixed bed catalytic reactor at 500 °C. The effect of catalyst acidity on product yield and composition has been studied by using three catalysts based on HZSM-5 zeolites with a SiO2/Al2O3 ratio of 30, 80, and 280. The maximum light olefin yield (58 wt %) has been obtained using the most acidic catalyst (SiO2/Al2O3 ratio of 30), with the individual yields of ethylene, propylene, and butenes being 9.5, 32, and 16.5 wt %, respectively. The results are a clear evidence of the higher efficiency of the two-step reaction system compared to the in situ catalytic pyrolysis (single-step), which is explained by the suitable combination of operating conditions in each one of the steps.
Ni catalysts were tested in the catalytic pyrolysis of biomass. The influence of Ni loading and various catalytic supports (ZrO2, Al2O3, ZrO2 + Al2O3, CeO2, SiO2) was studied. Although the gas phase was the main object of this study, solid and liquid residues were tested as well (mainly by TOC and GC-MS methods). Activity tests were performed in a batch reactor with mechanical stirring, equipped with on-line GC. Reaction was conducted at 700°C, with α-cellulose as a biomass model and with waste paper as an example of raw lignocellulosic material. Reactions in the presence of a catalyst gave a higher hydrogen yield. The most promising results were obtained with Ni/ZrO2.
An Al2O3-ZrO2 support was prepared by grafting a zirconium precursor onto the surface of commercial γ-Al2O3. A physical mixture of Al2O3-ZrO2 was also prepared for the purpose of comparison. Ni/Al2O3-ZrO2 catalysts were then prepared by an impregnation method, and were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). The effect ZrO2 and preparation method of Al2O3-ZrO2 on the performance of supported nickel catalysts in the steam reforming of LNG was investigated. The Al2O3-ZrO2 prepared by a grafting method was more efficient as a support for nickel catalyst than the physical mixture of Al2O3-ZrO2 in the hydrogen production by steam reforming of LNG. The well-developed tetragonal phase of ZrO2 and the high dispersion of ZrO2 on the surface of γ-Al2O3 were responsible for the enhanced catalytic performance of Ni/Al2O3-ZrO2 prepared by way of a grafting method.
Ni and Pt catalysts supported on α-Al2O3, α-Al2O3-ZrO2 and ZrO2 were studied in the dry reforming of methane to produce synthesis gas. All catalytic systems presented well activity levels with TOF (s−1) values between 1 and 3, being Ni based catalysts more active than Pt based catalysts. The selectivity measured at 650 °C, expressed by the molar ratio H2/CO reached values near to 1. Concerning stability, Pt/ZrO2, Pt/α-Al2O3-ZrO2 and Ni/α-Al2O3-ZrO2 systems clearly show lower deactivation levels than Ni/ZrO2 and Ni or Pt catalysts supported on α-Al2O3. The lowest deactivation levels observed in Ni and Pt supported on α-Al2O3-ZrO2, compared with Ni and Pt supported on α-Al2O3 can be explained by an inhibition of reactions leading to carbon deposition in systems having ZrO2. These results suggest that ZrO2 promotes the gasification of adsorbed intermediates, which are precursors of carbon formation and responsible for the main deactivation mechanism in dry reforming reaction.
Calcined scallop shell (CS) exhibits alkaline property with a porous structure, and could be applied for the adsorption and decomposition of biomass-derived tar. In this study, steam reforming of tar derived from pruned apple branch over CS was investigated in a fixed bed at 650 °C. It was found that CS had good activity for the steam reforming of tar to produce synthesis gas (syngas), and was able to be recycled. To promote the gas production efficiency, iron or nickel was supported on the CS, and used for the reforming of tar. The effect of heating rate on the gas production rate was investigated, and it was found that reduced iron- or nickel-supported CS showed better activities under the condition of rapid heating. Iron- or nickel-based catalyst in its oxide state was also investigated for the reforming of tar. No catalytic activity was found at the beginning, but good activity appeared after approximately 30 min of reaction when the metal oxide was reduced to its metallic form by the initially generated syngas (CO and H2) from the pyrolysis of biomass without the aid of catalyst. Iron and nickel in their metallic forms rather than their oxide ones were considered as active sites for the reforming of tar. Furthermore, the alkaline elements in the biomass, which could enhance the activity of the catalysts, were identified to be accumulated on the surface of the catalysts with the biomass-derived tar. As a result, a larger amount of syngas was produced when the regenerated catalysts were applied. Based on these experimental results, a possible catalytic process was proposed.