ArticlePDF Available

Hydrogen Production from Steam Reforming of Acetic Acid as a Model Compound of the Aqueous Fraction of Microalgae HTL Using Co-M/SBA-15 (M: Cu, Ag, Ce, Cr) Catalysts


Abstract and Figures

Hydrogen production derived from thermochemical processing of biomass is becoming an interesting alternative to conventional routes using fossil fuels. In this sense, steam reforming of the aqueous fraction of microalgae hydrothermal liquefaction (HTL) is a promising option for renewable hydrogen production. Since the HTL aqueous fraction is a complex mixture, acetic acid has been chosen as model compound. This work studies the modification of Co/SBA-15 catalyst incorporating a second metal leading to Co-M/SBA-15 (M: Cu, Ag, Ce and Cr). All catalysts were characterized by N2 physisorption, ICP-AES, XRD, TEM, H2-TPR, H2-TPD and Raman spectroscopy. The characterization results evidenced that Cu and Ag incorporation decreased the cobalt oxides reduction temperatures, while Cr addition led to smaller Co0 crystallites better dispersed on the support. Catalytic tests done at 600 °C, showed that Co-Cr/SBA-15 sample gave hydrogen selectivity values above 70 mol % with a significant reduction in coke deposition.
Content may be subject to copyright.
Catalysts 2019, 9, 1013; doi:10.3390/catal9121013
Hydrogen Production from Steam Reforming of Acetic
Acid as a Model Compound of the Aqueous Fraction
of Microalgae HTL Using Co-M/SBA-15
(M: Cu, Ag, Ce, Cr) Catalysts
Pedro J. Megía, Alicia Carrero *, José A. Calles and Arturo J. Vizcaíno *
Chemical and Environmental Engineering Group, Rey Juan Carlos University, c/Tulipán s/n,
28933 Móstoles, Spain; (P.J.M.); (J.A.C.)
* Correspondence: (A.C.); (A.J.V.)
Tel.: +34-91-488-8088 (A.C.); +34-91-488-8096 (A.J.V.)
Received: 30 October 2019; Accepted: 28 November 2019; Published: 2 December 2019
Abstract: Hydrogen production derived from thermochemical processing of biomass is becoming
an interesting alternative to conventional routes using fossil fuels. In this sense, steam reforming of
the aqueous fraction of microalgae hydrothermal liquefaction (HTL) is a promising option for
renewable hydrogen production. Since the HTL aqueous fraction is a complex mixture, acetic acid
has been chosen as model compound. This work studies the modification of Co/SBA-15 catalyst
incorporating a second metal leading to Co-M/SBA-15 (M: Cu, Ag, Ce and Cr). All catalysts were
characterized by N
physisorption, ICP-AES, XRD, TEM, H
-TPD and Raman spectroscopy.
The characterization results evidenced that Cu and Ag incorporation decreased the cobalt oxides
reduction temperatures, while Cr addition led to smaller Co
crystallites better dispersed on the
support. Catalytic tests done at 600 °C, showed that Co-Cr/SBA-15 sample gave hydrogen selectivity
values above 70 mol % with a significant reduction in coke deposition.
Keywords: microalgae; acetic acid; steam reforming; hydrogen; cobalt; mesostructured materials
1. Introduction
An increase in global pollution has resulted in a search for alternative energy resources that can
be substituted in place of widely used fossil fuels [1]. It is known that energy provided from hydrogen
does not result in pollutant emissions when it is used in fuel cell applications [2–4]. In addition,
hydrogen is extensively used in chemical and petroleum industries [5,6]. Nowadays, a
hydrogen-based energy system must use renewable energy sources to be sustainable. In this sense,
hydrogen production processes such as biomass gasification, and steam reforming (SR) of pyrolysis
bio-oil have been widely described in the literature [7–10]. However, the use of microalgae
hydrothermal liquefaction integrated with the steam reforming of the aqueous fraction is less known.
Microalgae HTL requires temperatures between 250–350 °C and high pressures that can maintain the
water coming from the microalgae crops in liquid state (40–250 bar). This process provides a great
advantage when compared to the traditional biomass pyrolysis process, as it does not require a
previous stage for biomass drying associated with high energy consumption [11–13]. Microalgae HTL
products are a complex mixture of different compounds where carboxylic acids, ketones, phenols,
aldehydes, fatty acids and nitrogen compounds [14] can be easily found along with a high water
content. For this reason, they are not suitable for use as a fuel. However, this worthless aqueous
fraction can be revalorized by hydrogen production through catalytic steam reforming [15,16] but the
Catalysts 2019, 9, 1013 2 of 20
complex composition mentioned above usually forces the use of model compounds [17–20]. Among
them, acetic acid is a major component, which can account even for the 56% of the water-soluble
products [17]. The overall equation of the acetic acid steam reforming is:
C2H4O2 + 2 H2O 2 CO2+ 4 H2 (1)
Nowadays, SR catalysts are a critical point of study where activity, hydrogen selectivity and
deactivation are the main concerns of the scientific community. Many papers can be found using
different active phases such as Ni, Co, Pt or Ru, with Ni being the most studied [21]. Hu et al. [22]
studied the performance of different transition metals supported over Al2O3 in acetic acid steam
reforming. Their study led to the conclusion that Ni and Co were more active than the other metals
tested (Fe and Cu). They attributed this behavior to the ability for cracking not only C-C bonds, but
also C-H bonds. However, Co-based catalysts have been less reported despite the fact that they also
provide high activity at moderate temperatures and also increases hydrogen yield [23,24].
Catalysts support selection is also an important point. For example, when Co was supported on
Al2O3 or TiO2 high metal dispersion was reported but cobalt aluminates or titanates were formed
avoiding the reduction of some Co species [25]. On the other hand, the interaction of Co with silica
has been studied leading to the conclusion that this support does not affect to its reducibility but
instead promote the sintering of cobalt particles in the calcination and reduction steps [26,27]. Apart
from that, there are other advanced supports such as SBA-15, which is a mesostructured material
with high surface area that may allow higher metal dispersion when compared with the amorphous
silica. Furthermore, SBA-15 presents an uniform distribution of mesopores that hinders the formation
of Co agglomerates preventing also catalysts deactivation due to metal sintering [28].
Co-based catalysts have shown deactivation through sintering and surface cobalt oxidation [21].
Pereira et al. [29] proposed the preparation of bimetallic catalysts to stabilize Co/SiO2 catalyst to
safeguard the Co particles in a reduced state during the reforming. Combining diverse metals in the
same carrier has been reported as an effective way to improve the catalyst performance by facilitating
the metal reducibility [30]. As reducibility promoters noble metals, transition metals or CeO2 among
others can be used. Wang et al. [31] reported that Cu addition to Ni/attapulgite catalyst decreased the
temperature for the reduction of nickel species. In line with this, Eschemann et al. [32] proved the
efficiency of silver as a reduction promoter in Co/TiO2 catalyst since Co-Ag bonds improve the
reducibility of cobalt oxides [32,33]. Besides, Harun et al. [34] achieved better Ni0 dispersion over
Al2O3 surface when Ag was included in the catalyst formulation. Similarly, it was described that
CeO2, presents a synergistic effect with cobalt oxides since more oxygen vacancies are formed leading
to higher reducibility [35]. In addition to promoting the cobalt reducibility to avoid possible
crystallites oxidation, it is necessary to obtain a small crystallite size in order to increase activity and
reduce the coke formation according to its growth mechanism [36]. Accordingly, Cerdá-Moreno et
al. [37] found that lower Co particle size for ethanol steam reforming led to better catalytic activity.
Recently, we have found that Ni-Cr/SBA-15 showed better catalytic behavior than Ni/SBA-15 in the
steam reforming of pyrolysis bio-oil aqueous fraction by decreasing Ni0 particles size [38].
Furthermore, Casanovas et al. [39,40] reported that the incorporation of Cr to Co/ZnO samples results
in better catalytic performance when these catalysts were tested in ethanol steam reforming.
So far, we have not been able to find any references using the promoters described above in
Co/SBA-15 catalysts to be tested in acetic acid steam reforming. Therefore, the main goal of this study
is the preparation of novel cobalt catalysts incorporating a second metal leading to Co-M/SBA-15 (M:
Cu, Ag, Ce and Cr) to achieve high hydrogen production rate through acetic acid steam reforming as
model compound of microalgae HTL aqueous fraction.
2. Results and Discussion
2.1. Catalysts Characterization
Nitrogen physisorption profiles displayed in Figure 1 show type IV isotherms with a H1-type
hysteresis loop according to the IUPAC classification, indicating the preservation of the initial
Catalysts 2019, 9, 1013 3 of 20
mesoestructure of SBA-15 used as the support of these samples. Textural properties calculated from
these analyses are summarized in Table 1 along with other physicochemical properties.
Figure 1. N2 physisorption isotherms of calcined (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-
15; (d) Co-Ce/SBA-15; (e) Co-Cr/SBA-15 catalysts at 77K.
Table 1. Physicochemical properties of Co-M/SBA-15 (M: Cu, Ag, Ce, Cr) catalysts.
Catalyst Coa (wt.%) Ma (wt.%) SBET (m2·g1) Dpore b (nm) Vpore c (cm3·g1) DCo0 d
(%) e
SBA-15 - - 550 ± 3 7.5 ± 0.1 0.97 ± 0.02 - -
Co/SBA-15 6.4 ± 0.1 - 503 ± 4 7.2 ± 0.1 0.83 ± 0.01 9.5 ± 0.5 7.5 ± 0.2
Co-Cu/SBA-15 6.5 ± 0.1 2.0 ± 0.1 476 ± 4 7.2 ± 0.1 0.79 ± 0.03 9.7 ± 0.3 6.3 ± 0.1
Co-Ag/SBA-15 6.4 ± 0.1 1.6 ± 0.1 419 ± 4 6.9 ± 0.1 0.71 ± 0.01 12.3 ± 0.4 3.9 ± 0.6
Co-Ce/SBA-15 6.6 ± 0.1 1.7 ± 0.1 494 ± 1 7.4 ± 0.1 0.84 ± 0.01 9.6 ± 0.2 6.5 ± 0.1
Co-Cr/SBA-15 6.8 ± 0.1 1.8 ± 0.1 469 ± 1 7.1 ± 0.1 0.81 ± 0.02 7.2 ± 0.1 9.9 ± 0.3
a Determined by ICP-AES (M: Cu, Ag, Ce or Cr) in reduced samples, b BJH desorption average pore
diameter, c Measured at P/P0 = 0.97, d Determined from XRD of reduced catalysts by Scherrer equation
from the (111) diffraction plane of Co0,e Determined from H2-TPD results using formula from Li et al.
[41] assuming H/Co = 1.
The metals loading is close to the nominal value used during the catalysts preparation. Metal
addition to bare SBA-15 leads to a decrease in BET surface area with Co-Ag/SBA-15 being the sample
with the smallest pore size, pore volume and surface area. This phenomena has been described
previously [42] and was ascribed to Ag structures growing in the mesopores of SBA-15. Similar
textural properties were found in Co-(Cu, Ce or Cr)/SBA-15 samples.
Figure 2 shows the XRD patterns of the calcined samples. Peaks corresponding to cubic Co3O4
appear in all samples (JCDPS 01-071-4921). Attending to Co-Cu/SBA-15 sample, a small peak at 38.3°
can be observed due to the formation of monoclinic CuO (JCDPS 01-089-2531). In case of
Co-Ce/SBA-15, two small peaks over 28.5° and 47.5° can be seen due to the presence of cubic CeO2
(JCDPS 01-089-8436). Ag and Cr oxides were not detected by XRD due to the overlap of the main
diffraction peaks of cubic Ag2O (JCPDS 00-012-0793), rhombohedral Cr2O3 (JCPDS 00-002-1362) and
cubic CoCr2O4 spinel (JCPDS 00-022-1084), with the Co3O4 pattern. The higher Co content compared
absorbed volume (a.u.)
Relative pressure (P/P
0.2 0.4 0.6 0.8
Catalysts 2019, 9, 1013 4 of 20
to Ag and Cr also contributes to the non-detection of Ag and Cr oxides by XRD as were observed in
previous works [43,44]. XRD patterns corresponding to Co-(Cu, Ag or Ce)/SBA-15 present narrower
Co3O4 peaks and slightly larger Co3O4 crystallites were obtained comparing when compared to
Co/SBA-15 sample.
Figure 2. XRD of calcined (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d) Co-Ce/SBA-15; (e)
Co-Cr/SBA-15 catalysts. Co3O4 crystallites sizes calculated from the (311) diffraction plane using
Scherrer equation are displayed on the right.
Figure 3 shows the TEM micrographs of calcined samples. Irregular metal oxides particles can
be observed, some of them formed in the channels of SBA-15, while other particles were formed over
the external surface as previously reported [43]. The presence of Co and promoters (Cu, Ag, Ce or
Cr) were evaluated in the corresponding sample by EDX indicating an intimate contact between Co
oxide and promoters. Co-Ag/SBA-15 catalyst has large metallic nanostructures through the SBA-15
channels and Ag2O particles can be also observed over the support [45]. The incorporation of high
Ag loadings (> 1wt. %) affects support structure and distribution of Ag2O particles over the catalyst
because the probability of Ag-Ag bond formation increases [32,33]. On the other side, it is noticeable
how Co-Cr/SBA-15 sample clearly shows the highest dispersion over the support with very small
metal oxide particles, which is in agreement with the lower metal diameter calculated from XRD
(Table 1).
30 40 50 60 70 80
± 0.2
± 0.4
± 0.2
Intensity (a.u.)
± 0.3
± 0.1
Catalysts 2019, 9, 1013 5 of 20
Figure 3. TEM micrographs of calcined samples (a): Co/SBA-15; (b): Co-Cu/SBA-15; (c): Co-Ag/SBA-
15; (d): Co-Ce/SBA-15; (e): Co-Cr/SBA-15.
Figure 4 displays the H
-TPR profiles of the calcined catalysts. In the case of Co/SBA-15 sample,
the reduction profile shows two main reduction stages. The first one with maxima found at 248–267
°C and a shoulder around 332 °C. These peaks are attributed to the reduction of Co
to CoO and
subsequently to Co
. The reduction stage at high temperature, with a maximum placed at 494 °C, can
be attributed to the presence of Co-oxide species with stronger interaction with the support [46]. Cu
addition led to a clear decrease of the reduction temperature as observed in Co-Cu/SBA-15 profile.
Catalysts 2019, 9, 1013 6 of 20
Figure 4. H2-TPR profiles for (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d) Co-Ce/SBA-15;
(e) Co-Cr/SBA-15 samples. Red. (%) data displayed on the right correspond to reducibility.
The reduction zone is located at temperatures between 140-260 °C with two maxima at 150 and
194 °C. Whereas the lower temperature peak is ascribed to the simultaneous reduction of CuO and
Co3O4 to Cu0 and CoO respectively, the other one is related to the reduction of CoO to Co0 [47]. This
effect of Cu in lowering reduction temperature of metal oxides was observed in previous works for
Ni-based catalysts [43]. Co-Ag/SBA-15 catalyst showed two clearly different reduction areas, also at
low temperature. While the zone over 267 °C is related to the Co oxides next to Ag, the other one
around 166 °C is attributed to the reduction of segregated Ag2O particles to Ag0 [48]. On the other
hand, Co-Ce/SBA-15 sample showed a reduction profile similar to Co/SBA-15 with the peak at 494
°C shifted to higher reduction temperature due to an emerging peak assigned to superficial cerium
oxide [49]. Finally, in the reduction profile of Co-Cr/SBA-15 had a new peak around 182 °C, probably
due to the reduction of Cr-oxides to Cr3+ which can be affected by the presence of Co3O4 [50] although
it could not be detected by XRD. The peak attributed to Co3O4 reduction at 271 °C remained unaltered
whereas the peak of CoO reduction shifts to higher temperatures due to the presence of Cr species
[51] or to the confinement of Co oxides into SBA-15 channels because of their smaller size. Based on
the literature, the most likely option is the formation of a cobalt chromate mixed oxide [52], although
none could be detected by XRD due to the overlap of the main diffraction lines of CoCr2O4 with those
of Co3O4. The XRD patterns of the samples after reduction at 700 °C under pure H2 flow are displayed
in Figure 5. No peaks ascribed to Co
3O4 pattern can be detected whereas cubic Co0 (JCDPS
00-001-1259) peaks corresponding to (111), (200) and (220) planes showing the reflection at 2θ = 44.4°,
51.3° and 75.4° can be observed in all samples after the reduction process.
200 400 600 800
± 4
± 1
± 2
± 2
± 3
consumption (a.u.)
Temperature (ºC)
a) 100
Catalysts 2019, 9, 1013 7 of 20
Figure 5. XRD of reduced (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d) Co-Ce/SBA-15; (e)
Co-Cr/SBA-15 catalysts at 700 °C.
Cubic Ag0 (JCDPS 00-043-1038) diffraction peaks arose in the Co-Ag/SBA-15 sample at 2θ = 38.1°,
64.5° and 77°, ascribed to (111), (200) and (220) reflection planes, respectively. In this case, some Co-
oxides could remain in this sample explaining its low reducibility (see Figure 4) but they were not
detected because there is an overlapping between Ag0 and Co3O4 patterns at 38.1° and 64.5°. In Co-
Cr/SBA-15 catalyst a peak placed at 2θ = 63.7° was assigned to rhombohedral Cr2O3 (JCDPS 00-002-
1362) probably coming from the release of CoO from the spinel CoCr2O4. No diffraction peaks of
cubic Cu0 (JCPDS 00-001-1241) were distinguished in Co-Cu/SBA-15 sample due to the overlapping
between Cu0 and Co0 diffraction peaks. Co-Ce/SBA-15 reduced sample showed only the diffraction
peak of metallic Co. The absence of CeO2 diffraction peaks prompted us to think about the formation
of a non-stoichiometric CeO2σ that cannot be detected by XRD [53].
Co0 crystallite sizes were calculated by the Scherrer equation from the diffraction plane (111). In
general, whereas Co-Cu/SBA-15 and Co-Ce/SBA-15 samples present a crystallite size similar to
Co/SBA-15, Co-Ag/SBA-15 had the largest crystallites (see Table 1) which differs from the literature
as silver loading in Co-Ag/SBA-15 is higher than in references [31,32]. In contrast, Co-Cr/SBA-15
presented the lowest Co crystallite size because making a parallelism with the paper of Amin et al.
[54] Cr-oxides can suppress the extension growth of Cu-oxides in that case, Co-oxides in our case.
H2-TPD analysis was carried out in order to measure the dispersion of the metallic phase over
the support. The results, summarized in Table 1, follow the opposite trend as Co0 crystallite sizes
calculated from the Scherrer equation. Co-Cr/SBA-15 sample reached the highest active phase
dispersion over the support. This effect can be clearly observed in Figure 6, where Co0 crystallite sizes
are displayed against dispersion and it is clear that the only promoter that improves the base
Co/SBA-15 catalyst is Cr. In addition, other authors have reported smaller crystallite size when Cr
was incorporated to the catalyst formulation suggesting the capacity of Cr2O3 to act as a textural
promoter preventing metallic sintering [55–57]. It should be noted that in a previous work we
reported the same behavior with Ni-Cr/SBA-15 sample [38,43], in line with the results obtained by
Xu et al. during the co-impregnation of Cr and Ni over char as support [58].
30 40 50 60 70 80
Intensity (a.u.)
Catalysts 2019, 9, 1013 8 of 20
Figure 6. Comparison between Co0 crystallites size and Dispersion over the SBA-15 material used as
support for (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d) Co-Ce/SBA-15; (e) Co-Cr/SBA-
2.2. Catalytic Tests
AASR (acetic acid steam reforming) reactions were carried out after the reduction of the
catalysts. All experiments were performed using an aqueous solution of acetic acid with a S/C molar
ratio = 2 and a WHSV = 30.1 h1 at atmospheric pressure and 600 °C using N2 as carrier gas. Conversion
data are not shown because all catalysts reached complete conversion along 5 h of time-on-stream,
which implies high activity for all the samples in acetic acid conversion at these reaction conditions.
However, different product distributions were achieved indicating different activities in acetic acid
steam reforming reaction, ascribed to the role of a second metal in secondary reactions. In this sense,
hydrogen and carbon co-products distribution (dry basis) are displayed in Figure 7.
Figure 7. Products distribution in outlet gas stream produced in the acetic acid steam reforming over
Co-M/SBA-15 (M: Cu, Ag, Ce, Cr) catalysts at T = 600 °C, P = 1 atm, time-on-stream = 5 h.
The H2 content expected at equilibrium at the experimental conditions, predicted by means of
the software GasEQ, based on the method of free Gibbs energy minimization, is also shown.
Regarding products distribution, all catalysts reached high hydrogen concentration, above 53%. As
known, Co-based catalysts allow the breaking of C-C bonds (only methane is produced as hydrogen-
containing product) but also of C-H bonds [22]. Moreover, an effective catalyst must also be active in
Dispersion (%)
equilibrium H
% mol
Co/SBA-15 Co-Cu/SBA-15 Co-Ag/SBA-15 Co-Ce/SBA-15 Co-Cr/SBA-15
Catalysts 2019, 9, 1013 9 of 20
WGS reaction in order to eliminate CO from the metal surface during steam reforming. Over Co,
methane reforming and WGS activity was presented and this clearly shown by products formation.
Among them, CO2 formation is highest and followed by CO, CH4, thus WGS is more pronounced
compared to other disproportionation and decomposition reactions. Cu, Ag and Ce addition to
Co/SBA-15 decreases the hydrogen content in the gas outlet stream in line with higher co-carbon
products percentages. In contrast, Co-Cr/SBA-15 reached the highest hydrogen concentration in the
product stream. This behavior is related to the small Co crystallite size (see Table 1) leading to higher
active sites surface area [59,60]. Therefore, Cr addition improved the catalytic performance by
preventing Co agglomeration. In fact, Casanovas et al. [40] have published similar behavior adding
Cr to Co/ZnO being more active and selective for ethanol steam reforming. On the other side,
Co-Ag/SBA-15 achieved the lowest hydrogen concentration and therefore carbon containing
products composition was higher, probably due to the pore blocking effect and the highest Co
crystallite size. Co-Cu/SBA-15 and Co-Ce/SBA-15 showed higher CO2/CO molar ratio compared to
the other samples (3/2) suggesting that the activity for WGS reaction was increased [60]. If WGS
reaction is favored, an increase in the hydrogen production is expected but the hydrogen content
reached with these two catalysts was lower than with Co/SBA-15 (CO2/CO ratio = 1.7) thus, it is
possible to assume that the presence of a second metal hinders reactants access to Co active centers,
thereby avoiding their catalytic role breaking C-H bonds. Finally, Co-Cu/SBA-15, Co-Ag/SBA-15 and
Co-Ce/SBA-15 showed an increase of CH4 from 2% to almost 5% in comparison to the Co/SBA-15
sample. CH4 formation can be due to the decomposition of acetic acid or methanation [61].
Particularly, Co-Cu/SBA-15 and Co-Ce/SBA-15 produce more CH4 in line with the reduction of H2
and CO content which indicates that Cu and Ce promote the methanation reaction (3H2 + CO CH4
+ H2O) [62]. Instead, the increase of produced methane with Co-Ag/SBA-15 could be due to the
decomposition of acetic acid since the CO content was kept constant while both CO2 and CH4
concentrations increase, which would be in accordance with the stoichiometry of the reaction
CH3COOH CH4 + CO2. However, other parallel and consecutive reactions varying the CO, CO2
and CH4 content can be taking place.
Regarding the evolution of H2 selectivity, calculated as the ratio between hydrogen produced
and 4 times the reacted acetic acid (stoichiometry), with reaction time showed in Figure 8 Co-Cu/SBA-
15 and Co-Ag/SBA-15 samples exhibited a decrease at 2 h but after that, it remains almost constant.
Regardless, the H2 selectivity of the rest of catalysts remains almost unaltered with time-on-stream.
Therefore, no deactivation was detected for Co/SBA-15, Co-Ce/SBA-15 and Co-Cr/SBA-15 samples.
In addition, it can be assessed that Co-Cr/SBA-15 sample also achieved the highest H2 selectivity close
to the thermodynamic value at the present reaction conditions. This result is promising compared to
those obtained by Ni-based catalysts widely referenced in literature for acetic acid steam reforming
reactions. In this sense, Thaicharoensutcharittham et al. [63] reported that Ni/Ce0.75Zr0.25O2 catalyst
with a Ni loading of 5 wt.% reached hydrogen selectivity of 33.54 mol % with a S/C = 1, and 64.39 mol
% using a S/C = 3. On the other hand, Wang et al. [64] achieved hydrogen selectivity between 54.5
and 70.9 mol % for reaction tests carried out at 550 °C and 650 °C respectively, with S/C = 3 using
Ni/Attapulgite catalysts. In another work, Nogueira et al.[65] published the catalytic performance of
Ni catalysts supported on (MgO)-modified γ-Al2O3 reaching, a H2 selectivity of 67.5 mol % at higher
S/C ratio (S/C = 4). Additionally, our group tested at similar operation conditions (600 °C, GHSV:
11000 h1) Ni-based catalysts in AASR with a S/C = 4 [38]. In that work, we achieved up to 60 mol %
of hydrogen content for both Ni/SBA-15 and Ni-Cr/SBA-15, which implied H2 selectivities between
56.6–59.9 mol %. These values are lower than those achieved with Co-M/SBA-15 catalysts in the
present work, even though lower S/C ratio has been used that should lead to worse catalytic results.
Despite differences in reaction conditions, mainly S/C molar ratio, these H2 selectivity values are
lower than that achieved by Co-Cr/SBA-15 sample. Furthermore, we also observed the beneficial
effect of adding Cr to catalysts in our recently published works [38,43], where we reached using Cr
as promoter added to Ni/SBA-15 catalysts, better catalytic performance using different feedstock in
steam reforming reaction.
Catalysts 2019, 9, 1013 10 of 20
Figure 8. Hydrogen selectivity of gas stream produced in the acetic acid steam reforming over (a)
Co-Cr/SBA-15; (b) Co/SBA-15; (c) Co-Ce/SBA-15; (d) Co-Ag/SBA-15; (e) Co-Cu/SBA-15 catalysts at T
= 600 °C, P = 1 atm.
Coke formation during steam reforming has been reported as the main cause of SR catalyst
deactivation [36]. It must be emphasized that catalyst deactivation is not only related to the amount
of coke, but also to the nature of the coke formed, the morphology and the location over the catalyst
structure [66]. In this sense, XRD patterns of used catalysts after 5 h (TOS) are shown in Figure 9.
Figure 9. XRD patterns of used (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d)
Co-Ce/SBA-15; (e) Co-Cr/SBA-15 catalysts. Co0 crystallites sizes calculated from the (111) diffraction
plane using Scherrer equation are displayed on the right.
Peaks corresponding to cubic Co0 (JCDPS 00 001 1259) at 2θ = 44.4°, 51.3° and 75.4° can be still
distinguished. In contrast to reduced samples (Figure 5), reflection peaks corresponding to graphitic
carbon (JCDPS 00-041-1487) at 2θ = 26.5°, 42.6°, 53.9° and 78.8° ascribed to (002), (100), (004) and (006)
reflection planes, respectively, appear as a consequence of the coke deposition along the acetic acid
steam reforming being more pronounced in Co-Ag/SBA-15 sample. Cobalt crystallites sizes of used
time (h)
10 20 30 40 50 60 70 80
Intensity (a.u)
± 0.2
± 0.4
10.2 nm
± 0.5
± 0.3
± 0.2
Catalysts 2019, 9, 1013 11 of 20
catalysts (calculated from Scherrer equation) are shown on the right side of Figure 9. Comparing
these results with those found in reduced samples (Table 1), it can be concluded that cobalt crystallites
sizes were very similar, which indicates no significant sintering throughout the reforming reaction.
TGA can be used for the identification of the type of coke formed during the reaction since more
ordered coke will need higher temperature to be oxidized [67]. It is normally reported that
amorphous carbon is more reactive than graphitic in reactions with O2 [68] because it oxidizes at low
temperatures whereas filamentous or graphitic carbon does at higher temperatures [69–71]. Figure
10 displays the derivative thermogravimetric (DTG) curves of the used catalysts along with the
amount of coke formed during the reaction in terms of mgcoke·gcat1·h1.
Figure 10. DTG curves of used (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d)
Co-Ce/SBA-15; (e) Co-Cr/SBA-15 samples after 5 h time-on-stream.
There are significant differences in the total coke content, in the order Co-Ag/SBA-15 > Co-
Ce/SBA-15 > Co-Cu/SBA-15 > Co/SBA-15 > Co-Cr/SBA-15 which follows the reverse order of the
hydrogen content in the outlet stream during AASR (see Figure 6). In general, all DTG profiles show
a maximum around 500 °C and a shoulder around 550 °C, indicating the formation of some kind of
carbon nanofibers with different ordering degree [69,70]. Co-Ag/SBA-15 showed a maximum around
441 °C which can be related to the formation of some defective carbon deposits. Co-Ag/SBA-15
obtained the worst catalytic results (high CH4 concentration and the lowest H2 concentration), in line
with the highest carbon deposition. Besides, it is noteworthy that Co-Cr/SBA-15 reduced the coke
production two times compared to Co/SBA-15. It is known that Cr2O3 has been used as an oxide
catalyst with outstanding carbon deposition resistance properties [72,73]. In our case, the reduction
in carbon deposition can be also ascribed to the role of chromium avoiding the formation of large Co
crystallites as it could be observed by TEM and measured by the Scherrer equation, because smaller
Co crystallites will prevent the initiation of carbon nucleation leading to coke formation [74]. On the
other hand, Cr2O3 has catalytic activity in the WGS reaction, lowering the CO concentration into the
gas phase surrounding the catalytic bed, thus favoring the formation of H2 and CO2 [75]. In this sense,
the extent Boudouard reaction (2 CO (g) CO2 (g) + C (s)), which is one of the main routes for coking,
will be reduced.
200 300 400 500 600 700 800 900
15.4 ± 1.5 mg
90.0 ± 8.9 mg
282.6 ± 28.3 mgcoke·gcat-1·h-1
51.6 ± 5.2 mgcoke·gcat-1·h-1
Deriv. Weight (a.u.)
Temperature (ºC)
34.8 ± 3.5 mgcoke·gcat-1·h-1
Catalysts 2019, 9, 1013 12 of 20
Used catalysts were also analyzed by TEM as shown in Figure 11. In all cases, carbon nanofibers
with different ordering degree can be observed. Besides, Co-Ag/SBA-15 micrograph shows some
zones of defective coke deposits, in concordance with DTG results.
Figure 11. TEM micrographs of used (a): Co/SBA-15; (b): Co-Cu/SBA-15; (c): Co-Ag/SBA-15; (d): Co
Ce/SBA 15; (e): Co-Cr/SBA-15 (5 h time-on-stream at 600 °C).
Finally, the Raman spectra of used catalysts in the range 1200–1700 cm
are presented in Figure
12. As it can be observed, two main bands appear in all cases, at 1330–1340 (D-band) and 1586–1591
(G-band). G-band is ascribed to the stretching mode of carbon sp
bonds of condensed graphitic
aromatic structures such as graphite layer [76], whereas D-band is related to the carbon atoms
vibration of disordered aromatic structures such as amorphous or defective filamentous carbon
[70,77–79]. The presence of both bands exhibits the heterogeneity of carbon species constituting the
coke formed during the AASR reaction. It has been reported that the intensity of the D band relative
to the G band can be used as a qualitative measure of the formation of different kinds of carbon with
different degree of graphitization or disorder in the carbon structure [78–80]. Smaller I
indicate higher crystallinity due to higher contribution of the graphitic carbon structures formed
[81,82] but it also implies more layers constituting the deposited carbon [83]. In these sense, the
estimated values are summarized also in Figure 12. As can be seen, the I
ratio decreases in the
following order: Co-Cr/SBA-15 (I
= 0.80) > Co/SBA-15 (I
= 0.65) > Co-Ce/SBA-15 (I
= 0.61) >
Co-Ag/SBA-15 (I
= 0.53) > Co-Cu/SBA-15 (I
= 0.48). These results indicate that carbon
deposition over the Co-Cu/SBA-15 sample occurs in larger extent on the Co surface when compared
with the other samples, leading to the growth of well-ordered carbon, which may be responsible of
catalyst deactivation since it act as a shell covering the active Co sites layer by layer [80]. It must be
highlighted that the H
selectivity represented in Figure 8, decreases in the same order as I
Therefore, the H
selectivity is directly related to the kind of carbon deposited on the catalyst.
Catalysts 2019, 9, 1013 13 of 20
Figure 12. Raman spectra of used (a) Co/SBA-15; (b) Co-Cu/SBA-15; (c) Co-Ag/SBA-15; (d)
Co-Ce/SBA-15; (e) Co-Cr/SBA-15 catalysts.
An AASR test done at long time-on-stream displayed in Figure 13 showed that Co-Cr/SBA-15
achieved good stability after 50 h time-on-stream. Conversion values were near 95% at the end of the
reaction, while almost constant hydrogen selectivity (~72 mol %) was obtained. These results
evidence that Co-Cr/SBA-15 sample is a promising option for acetic acid steam reforming, since
hydrogen selectivity remains close to the equilibrium value for a long period and, in addition, this
value is greater than those obtained with the Ni-based catalysts described in literature.
Figure 13. Acetic acid conversion () and hydrogen selectivity () during stability test of Co-Cr/SBA-
15 catalyst at T = 600 °C, P = 1 atm.
3. Experimental Section
3.1. Catalysts Synthesis
Mesostructured SBA-15 material, synthesized using the hydrothermal method described
elsewhere [84], was used as catalysts support. Pluronic 123 and TEOS were used as surfactant and
silica precursor (Aldrich, St. Louis, MO, USA) respectively.
Synthesis of Co-M/SBA-15 (M: Cu, Ag, Ce or Cr) catalysts was accomplished by the incipient
wetness impregnation method described in previous work [85]. Metal loading was selected as 7 wt.%
1300 1400 1500 1600 1700
ID/IG= 0.80
ID/IG= 0.61
ID/IG= 0.53
ID/IG= 0.48
Intensity (a.u.)
Raman shift (cm
ID/IG= 0.65
10 20 30 40 50
mol %
time (h)
Catalysts 2019, 9, 1013 14 of 20
of Co and 2 wt.% of promoter [86]. In this way, mixed aqueous solutions of the corresponding nitrates
were used for the co-impregnation: Co(NO3)2·6H2O (Acros Organics, Morris Plains, NJ, USA) and
Cu(NO3)2·3H2O, Cr(NO3)3·9H2O, Ce(NO3)3·6H2O, AgNO3 (Aldrich, St. Louis, MO, USA).
Subsequently, the prepared samples were calcined under air at 550 °C.
3.2. Catalysts Characterization
N2 adsorption/desorption at 77 K on a TRISTAR 3000 sorptometer (Micromeritics, Norcross, GA,
USA) was used for the measurement of textural properties. Prior to the analysis samples were
outgassed under vacuum at 200 °C for 4 h. To determine the chemical composition of the catalysts,
ICP-AES technique was used. The equipment was a VISTA-PRO AX CCD-Simultaneous ICP-AES
spectrophotometer (Varian, Palo Alto, CA, USA). Samples were previously treated by acidic
digestion. XRD measurements were recorded using an X’pert PRO diffractometer (Philips,
Eindhoven, The Netherlands) using Cu Kα radiation. The Scherrer equation was used to estimate the
metal crystallites mean diameter. Reducibility of the samples was studied by TPR analyses. A
Micromeritics (Norcross, GA, USA) AUTOCHEM 2910 system was used. The experiment is carried
out flowing 35 N mL/min of gas (10% H2/Ar) through the sample and increasing temperature up to
980 °C with a 5 °C/min heating ramp. Samples were previously outgassed under Ar flow at 110 °C
for 30 min. Co dispersion of the catalysts was determined by hydrogen TPD in the same apparatus.
For that, the samples were first reduced under 35 N mL/min of gas (10% H2/Ar), then cooled to 50 °C,
and saturated with H2. After that, the physically absorbed H2 is removed by flushing Ar and finally
heated up to 700 °C at 5 °C/min in Ar flow (30 N mL/min). TEM micrographs were obtained on a 200
kV JEM 2100 microscope (JEOL, Tokyo, Japan), with a resolution of 0.25 nm at the National Centre
for Electron Microscopy (CNME, Complutense University of Madrid, Madrid, Spain). It also has the
possibility to achieve microanalysis results by energy dispersive X-ray spectroscopy (EDX). Samples
preparation involve their suspension in acetone and subsequently deposition on a carbon-coated
copper or nickel grid. Carbon deposited during catalytic tests was measured by thermogravimetric
analysis (TGA), TEM and Raman spectroscopy. TGA analysis were performed in airflow with a
heating rate of 5 °C/min up to 1000 °C on a SDT 2960 thermobalance (TA Instruments, New Castle,
DE, USA). Raman spectra were recorded using a NRS-5000/7000 series Raman spectrometer (JASCO,
Tokyo, Japan) at the IMDEA Energy Institute.
3.3. Catalytic Tests
Acetic acid steam reforming reactions were performed at 600 °C on a MICROACTIVITY-PRO
unit (PID Eng. & Tech. S.L., Alcobendas, Madrid, Spain) as described in previous works [7,38,85,87].
The reactor consists in a fixed-bed tubular reactor in stainless steel 316 (i.d. = 9.2 mm, L = 300 mm).
The reactor is located inside an electric oven of low thermal, where temperature in the catalytic bed
was measured by means of a K-thermocouple. All the components inside the hot box were
maintained at 200 °C to prevent condensation in the pipes and to preheat the reactants. A schematic
diagram is displayed in Figure 14.
Catalysts 2019, 9, 1013 15 of 20
Figure 14. Schematic diagram of the catalytic testing setup [38].
The reactions were carried out isothermally at atmospheric pressure. Before tests, all catalysts
were reduced under pure hydrogen (30 mL/min) up to 700 °C with a heating rate of 2 °C/min.
Temperature was maintained for 30 min. Reaction feed was a mixture of acetic acid and water using
a steam to carbon molar ratio of 2, using N2 as carrier and internal standard (GHSV = 11,000 h1). The
composition of the outlet gas was measured online with an 490 Micro-GC (Agilent, Santa Clara, CA,
USA) equipped with a thermal conductivity detector (TCD), a PoraPlot U column (10 m) and a
Molecular Sieve 5A column (20 m) using He and Ar as carrier gas, respectively. Condensable vapors
were trapped in the condenser at 4 °C and analyzed in a Varian (Palo Alto, CA, USA) CP-3900
chromatograph equipped with a CP-WAX 52 CB (30 m × 0.25 mm, DF = 0.25) column and flame
ionization detector (FID).
4. Conclusions
The incorporation of a second metal like Cu, Ag, Ce or Cr into Co/SBA-15 sample catalyst
resulted in bimetallic catalysts with very different properties and catalytic behavior in acetic acid
steam reforming. Co-Ag/SBA-15 presented some pore blockage of the SBA-15 structure due to the
presence of isolated silver oxide particles. Cu and Ag addition to Co/SBA-15 led to a significant
decrease in the reduction temperature, as shown in H2-TPR profiles. Cu addition to Co/SBA-15 favors
Co oxide reducibility, while maintaining almost unaltered Co0 crystallites size. In contrast, Co-
Ag/SBA-15 showed also lower reduction temperatures but larger Co0 crystallites than Co/SBA-15.
However, Ce addition does not affect significantly neither reducibility nor Co0 crystallite size. Finally,
Cr addition to Co/SBA-15 strongly decreases Co crystallites size, induced by the presence of
chromium oxides, improving metal dispersion with a slight decrease in the reduction temperature.
Regarding acetic acid steam reforming, Co-Cu/SBA-15 and Co-Ag/SBA-15 gave lower hydrogen
selectivity than unmodified Co/SBA-15 catalyst. However, Cr addition improved the catalytic
behavior reaching the highest hydrogen selectivity next to the thermodynamic equilibrium. After the
steam reforming tests, cobalt crystallites sizes in the used catalysts were very similar to those in fresh
samples, indicating that coke deposition and not sintering is the cause of catalysts deactivation.
Catalysts 2019, 9, 1013 16 of 20
Besides, the amount of coke formed on Co-Cr/SBA-15 was much lower than on the rest of the catalysts
after 5 h of time on stream. Another difference resided in the nature of coke deposited because
disordered aromatic structures such as amorphous or defective filamentous carbon were formed in a
higher extent on Co-Cr/SBA-15 (ID/IG = 0.80) while the contribution of condensed graphitic aromatic
structures increased in Co-Cu/SBA-15 (ID/IG = 0.48). Thus, Cr addition to Co/SBA-15 resulted in the
best catalytic performance on acetic acid steam reforming, but Cr toxicity opens the way to the search
for other metals providing similar catalytic properties.
Author Contributions: Conceptualization, A.C. and J.A.C.; methodology, A.J.V.; validation, A.J.V.; formal
analysis, A.C.; investigation, P.J.M.; writing—original draft preparation, P.J.M.; writing—review and editing,
A.C., J.A.C. and A.J.V.; supervision, A.C., J.A.C. and A.J.V.; project administration, A.C. and J.A.C.; funding
acquisition, A.C. and J.A.C.
Funding: This research was funded by the Spanish Ministry of Economy and Competiveness (project ENE2017-
83696-R) and the Regional Government of Madrid (project S2018/EMT-4344).
Acknowledgments: The authors acknowledge the IMDEA Energy Institute and the Complutense University of
Madrid for the Raman and TEM analyses, respectively.
Conflicts of Interest: The authors declare no conflict of interest.
1. Dobosz, J.; Małecka, M.; Zawadzki, M. Hydrogen generation via ethanol steam reforming over Co/HAp
catalysts. J. Energy Inst. 2018, 91, 411–423, doi:10.1016/j.joei.2017.02.001.
2. Vizcaíno, A.J.; Carrero, A.; Calles, J.A. Hydrogen Production from Bioethanol; Nova Science Publishers: New
York, NY, USA, 2012.
3. Agency, I.E. Hydrogen Production and Storage: R&D Priorities and Gaps; IEA Publications: Paris, France, 2006.
4. Ruocco, C.; Palma, V.; Ricca, A. Kinetics of Oxidative Steam Reforming of Ethanol Over Bimetallic Catalysts
Supported on CeO2–SiO2: A Comparative Study. Top. Catal. 2019, 62, 467–478, doi:10.1007/s11244-019-
5. He, L.; Parra, J.M.S.; Blekkan, E.A.; Chen, D. Towards efficient hydrogen production from glycerol by
sorption enhanced steam reforming. Energy Environ. Sci. 2010, 3, 1046–1056, doi:10.1039/B922355J.
6. Wang, Y.; Wang, C.; Chen, M.; Tang, Z.; Yang, Z.; Hu, J.; Zhang, H. Hydrogen production from steam
reforming ethanol over Ni/attapulgite catalysts - Part I: Effect of nickel content. Fuel Process. Technol. 2019,
192, 227–238, doi:10.1016/j.fuproc.2019.04.031.
7. Carrero, A.; Vizcaíno, A.J.; Calles, J.A.; García-Moreno, L. Hydrogen production through glycerol steam
reforming using Co catalysts supported on SBA-15 doped with Zr, Ce and La. J. Energy Chem. 2017, 26, 42–
48, doi:10.1016/j.jechem.2016.09.001.
8. Shayan, E.; Zare, V.; Mirzaee, I. Hydrogen production from biomass gasification; a theoretical comparison
of using different gasification agents. Energy Convers. Manag. 2018, 159, 30–41,
9. Turner, J.; Sverdrup, G.; Mann, M.K.; Maness, P.C.; Kroposki, B.; Ghirardi, M.; Blake, D. Renewable
hydrogen production. Int. J. Energy Res. 2008, 32, 379–407, doi:10.1002/er.1372.
10. Zheng, J.-L.; Zhu, Y.-H.; Zhu, M.-Q.; Kang, K.; Sun, R.-C. A review of gasification of bio-oil for gas
production. Sustain. Energy Fuels 2019, 3, 1600–1622, doi:10.1039/C8SE00553B.
11. López Barreiro, D.; Prins, W.; Ronsse, F.; Brilman, W. Hydrothermal liquefaction (HTL) of microalgae for
biofuel production: State of the art review and future prospects. Biomass Bioenergy 2013, 53, 113–127,
12. Chen, W.-H.; Lin, B.-J.; Huang, M.-Y.; Chang, J.-S. Thermochemical conversion of microalgal biomass into
biofuels: A review. Bioresour. Technol. 2015, 184, 314–327, doi:10.1016/j.biortech.2014.11.050.
13. Chiaramonti, D.; Prussi, M.; Buffi, M.; Rizzo, A.M.; Pari, L. Review and experimental study on pyrolysis
and hydrothermal liquefaction of microalgae for biofuel production. Appl. Energy 2017, 185, 963–972,
14. Guo, Y.; Yeh, T.; Song, W.; Xu, D.; Wang, S. A review of bio-oil production from hydrothermal liquefaction
of algae. Renew. Sustain. Energy Rev. 2015, 48, 776–790, doi:10.1016/j.rser.2015.04.049.
Catalysts 2019, 9, 1013 17 of 20
15. Jacobson, K.; Maheria, K.C.; Kumar Dalai, A. Bio-oil valorization: A review. Renew. Sustain. Energy Rev.
2013, 23, 91–106, doi:10.1016/j.rser.2013.02.036.
16. Remón, J.; Broust, F.; Volle, G.; García, L.; Arauzo, J. Hydrogen production from pine and poplar bio-oils
by catalytic steam reforming. Influence of the bio-oil composition on the process. Int. J. Hydrog. Energy 2015,
40, 5593–5608, doi:10.1016/j.ijhydene.2015.02.117.
17. Zhou, D.; Zhang, L.; Zhang, S.; Fu, H.; Chen, J. Hydrothermal Liquefaction of Macroalgae Enteromorpha
prolifera to Bio-oil. Energy Fuels 2010, 24, 4054–4061, doi:10.1021/ef100151h.
18. Yang, C.; Jia, L.; Chen, C.; Liu, G.; Fang, W. Bio-oil from hydro-liquefaction of Dunaliella salina over
Ni/REHY catalyst. Bioresour. Technol. 2011, 102, 4580–4584, doi:10.1016/j.biortech.2010.12.111.
19. Jena, U.; Das, K.C. Comparative Evaluation of Thermochemical Liquefaction and Pyrolysis for Bio-Oil
Production from Microalgae. Energy Fuels 2011, 25, 5472–5482, doi:10.1021/ef201373m.
20. Maddi, B.; Panisko, E.; Wietsma, T.; Lemmon, T.; Swita, M.; Albrecht, K.; Howe, D. Quantitative
characterization of the aqueous fraction from hydrothermal liquefaction of algae. Biomass Bioenergy 2016,
93, 122–130, doi:10.1016/j.biombioe.2016.07.010.
21. Silva, J.M.; Soria, M.A.; Madeira, L.M. Challenges and strategies for optimization of glycerol steam
reforming process. Renew. Sustain. Energy Rev. 2015, 42, 1187–1213, doi:10.1016/j.rser.2014.10.084.
22. Hu, X.; Lu, G. Comparative study of alumina-supported transition metal catalysts for hydrogen generation
by steam reforming of acetic acid. Appl. Catal. B Environ. 2010, 99, 289–297, doi:10.1016/j.apcatb.2010.06.035.
23. Banach, B.; Machocki, A.; Rybak, P.; Denis, A.; Grzegorczyk, W.; Gac, W. Selective production of hydrogen
by steam reforming of bio-ethanol. Catal. Today 2011, 176, 28–35, doi:10.1016/j.cattod.2011.06.006.
24. Ishihara, A.; Andou, A.; Hashimoto, T.; Nasu, H. Steam reforming of ethanol using novel carbon-oxide
composite-supported Ni, Co and Fe catalysts. Fuel Process. Technol. 2020, 197, 106203,
25. Khodakov, A.Y.; Chu, W.; Fongarland, P. Advances in the Development of Novel Cobalt FischerTropsch
Catalysts for Synthesis of Long-Chain Hydrocarbons and Clean Fuels. Chem. Rev. 2007, 107, 1692–1744,
26. Llorca, J.; Dalmon, J.-A.; Ramı́rez de la Piscina, P.; Homs, N.S. In situ magnetic characterisation of
supported cobalt catalysts under steam-reforming of ethanol. Appl. Catal. A Gen. 2003, 243, 261–269,
27. Tsoncheva, T.; Ivanova, L.; Minchev, C.; Fröba, M. Cobalt-modified mesoporous MgO, ZrO2, and CeO2
oxides as catalysts for methanol decomposition. J. Colloid Interface Sci. 2009, 333, 277–284,
28. Calles, J.A.; Carrero, A.; Vizcaíno, A.J. Ce and La modification of mesoporous Cu–Ni/SBA-15 catalysts for
hydrogen production through ethanol steam reforming. Microporous Mesoporous Mater. 2009, 119, 200–207,
29. Pereira, E.B.; Homs, N.; Martí, S.; Fierro, J.L.G.; Ramírez de la Piscina, P. Oxidative steam-reforming of
ethanol over Co/SiO2, Co–Rh/SiO2 and Co–Ru/SiO2 catalysts: Catalytic behavior and
deactivation/regeneration processes. J. Catal. 2008, 257, 206–214, doi:10.1016/j.jcat.2008.05.001.
30. Chen, G.; Tao, J.; Liu, C.; Yan, B.; Li, W.; Li, X. Hydrogen production via acetic acid steam reforming: A
critical review on catalysts. Renew. Sustain. Energy Rev. 2017, 79, 1091–1098, doi:10.1016/j.rser.2017.05.107.
31. Wang, Y.; Chen, M.; Yang, Z.; Liang, T.; Liu, S.; Zhou, Z.; Li, X. Bimetallic Ni-M (M=Co, Cu and Zn)
supported on attapulgite as catalysts for hydrogen production from glycerol steam reforming. Appl. Catal.
A Gen. 2018, 550, 214–227, doi:10.1016/j.apcata.2017.11.014.
32. Eschemann, T.O.; Oenema, J.; de Jong, K.P. Effects of noble metal promotion for Co/TiO2 Fischer-Tropsch
catalysts. Catal. Today 2016, 261, 60–66, doi:10.1016/j.cattod.2015.06.016.
33. Jermwongratanachai, T.; Jacobs, G.; Ma, W.; Shafer, W.D.; Gnanamani, M.K.; Gao, P.; Kitiyanan, B.; Davis,
B.H.; Klettlinger, J.L.S.; Yen, C.H.; et al. Fischer–Tropsch synthesis: Comparisons between Pt and Ag
promoted Co/Al2O3 catalysts for reducibility, local atomic structure, catalytic activity, and oxidation–
reduction (OR) cycles. Appl. Catal. A Gen. 2013, 464-465, 165-180, doi:10.1016/j.apcata.2013.05.040.
34. Harun, N.; Abidin, S.Z.; Osazuwa, O.U.; Taufiq-Yap, Y.H.; Azizan, M.T. Hydrogen production from
glycerol dry reforming over Ag-promoted Ni/Al2O3. Int. J. Hydrog. Energy 2018,
Catalysts 2019, 9, 1013 18 of 20
35. Konsolakis, M.; Sgourakis, M.; Carabineiro, S.A.C. Surface and redox properties of cobalt–ceria binary
oxides: On the effect of Co content and pretreatment conditions. Appl. Surf. Sci. 2015, 341, 48–54,
36. Trimm, D.L. Coke formation and minimisation during steam reforming reactions. Catal. Today 1997, 37,
233–238, doi:10.1016/S0920-5861(97)00014-X.
37. Cerdá-Moreno, C.; Da Costa-Serra, J.F.; Chica, A. Co and La supported on Zn-Hydrotalcite-derived
material as efficient catalyst for ethanol steam reforming. Int. J. Hydrog. Energy 2019, 44, 12685–12692,
38. Calles, J.A.; Carrero, A.; Vizcaíno, A.J.; García-Moreno, L.; Megía, P.J. Steam Reforming of Model Bio-Oil
Aqueous Fraction Using Ni-(Cu, Co, Cr)/SBA-15 Catalysts. Int. J. Mol. Sci. 2019, 20, 512.
39. Casanovas, A.; Roig, M.; de Leitenburg, C.; Trovarelli, A.; Llorca, J. Ethanol steam reforming and water gas
shift over Co/ZnO catalytic honeycombs doped with Fe, Ni, Cu, Cr and Na. Int. J. Hydrog. Energy 2010, 35,
7690–7698, doi:10.1016/j.ijhydene.2010.05.099.
40. Casanovas, A.; de Leitenburg, C.; Trovarelli, A.; Llorca, J. Catalytic monoliths for ethanol steam reforming.
Catal. Today 2008, 138, 187–192, doi:10.1016/j.cattod.2008.05.028.
41. Li, Z.; Si, M.; Li, X.; Lv, J. Effects of titanium silicalite and TiO2 nanocomposites on supported Co-based
catalysts for Fischer–Tropsch synthesis. Appl. Organomet. Chem. 2019, 33, e4640, doi:10.1002/aoc.4640.
42. Tang, Y.; Yang, M.; Dong, W.; Tan, L.; Zhang, X.; Zhao, P.; Peng, C.; Wang, G. Temperature difference effect
induced self-assembly method for Ag/SBA-15 nanostructures and their catalytic properties for epoxidation
of styrene. Microporous Mesoporous Mater. 2015, 215, 199–205, doi:10.1016/j.micromeso.2015.05.040.
43. Carrero, A.; Calles, J.A.; García-Moreno, L.; Vizcaíno, A.J. Production of Renewable Hydrogen from
Glycerol Steam Reforming over Bimetallic Ni-(Cu,Co,Cr) Catalysts Supported on SBA-15 Silica. Catalysts
2017, 7, 55.
44. Vizcaíno, A.J.; Carrero, A.; Calles, J.A. Hydrogen production by ethanol steam reforming over Cu–Ni
supported catalysts. Int. J. Hydrog. Energy 2007, 32, 1450–1461, doi:10.1016/j.ijhydene.2006.10.024.
45. Sun, X.; Sun, L.; Wang, J.; Yan, Y.; Wang, M.; Xu, R. Confination of Ag nanostructures within SBA-15 by a
“two solvents” reduction technique. J. Taiwan Inst. Chem. Eng. 2015, 57, 139–142,
46. Martı́nez, A.; López, C.; Márquez, F.; Dı́az, I. Fischer–Tropsch synthesis of hydrocarbons over mesoporous
Co/SBA-15 catalysts: The influence of metal loading, cobalt precursor, and promoters. J. Catal. 2003, 220,
486–499, doi:10.1016/S0021-9517(03)00289-6.
47. Fierro, G.; Lo Jacono, M.; Inversi, M.; Dragone, R.; Porta, P. TPR and XPS study of cobalt–copper mixed
oxide catalysts: Evidence of a strong Co–Cu interaction. Top. Catal. 2000, 10, 39–48,
48. Aspromonte, S.G.; Miró, E.E.; Boix, A.V. FTIR studies of butane, toluene and nitric oxide adsorption on Ag
exchanged NaMordenite. Adsorption 2012, 18, 1–12, doi:10.1007/s10450-011-9370-2.
49. Lin, S.S.Y.; Kim, D.H.; Ha, S.Y. Metallic phases of cobalt-based catalysts in ethanol steam reforming: The
effect of cerium oxide. Appl. Catal. A Gen. 2009, 355, 69–77, doi:10.1016/j.apcata.2008.11.032.
50. Yun, D.; Baek, J.; Choi, Y.; Kim, W.; Jong Lee, H.; Yi, J. Promotional Effect of Ni on a CrOx Catalyst
Supported on Silica in the Oxidative Dehydrogenation of Propane with CO2. ChemCatChem 2012, 4,
51. Chen, J.; Zhang, X.; Arandiyan, H.; Peng, Y.; Chang, H.; Li, J. Low temperature complete combustion of
methane over cobalt chromium oxides catalysts. Catal. Today 2013, 201, 12–18,
52. Zoican Loebick, C.; Lee, S.; Derrouiche, S.; Schwab, M.; Chen, Y.; Haller, G.L.; Pfefferle, L. A novel synthesis
route for bimetallic CoCr–MCM-41 catalysts with higher metal loadings. Their application in the high yield,
selective synthesis of Single-Wall Carbon Nanotubes. J. Catal. 2010, 271, 358–369,
53. Scheffe, J.R.; Steinfeld, A. Thermodynamic Analysis of Cerium-Based Oxides for Solar Thermochemical
Fuel Production. Energy Fuels 2012, 26, 1928–1936, doi:10.1021/ef201875v.
54. Amin, N.A.S.; Tan, E.F.; Manan, Z.A. SCR of NOx by C3H6: Comparison between Cu/Cr/CeO2 and
Cu/Ag/CeO2 catalysts. J. Catal. 2004, 222, 100–106, doi:10.1016/j.jcat.2003.10.005.
55. Cheng, W.-H.; Chen, I.; Liou, J.-S.; Lin, S.-S. Supported Cu Catalysts with Yttria-Doped Ceria for Steam
Reforming of Methanol. Top. Catal. 2003, 22, 225–233, doi:10.1023/a:1023523903281.
Catalysts 2019, 9, 1013 19 of 20
56. Huang, X.; Ma, L.; Wainwright, M.S. The influence of Cr, Zn and Co additives on the performance of
skeletal copper catalysts for methanol synthesis and related reactions. Appl. Catal. A Gen. 2004, 257, 235–
243, doi:10.1016/j.apcata.2003.07.012.
57. Wang, Z.; Xi, J.; Wang, W.; Lu, G. Selective production of hydrogen by partial oxidation of methanol over
Cu/Cr catalysts. J. Mol. Catal. A Chem. 2003, 191, 123–134, doi:10.1016/S1381-1169(02)00352-7.
58. Xu, L.; Duan, L.E.; Tang, M.; Liu, P.; Ma, X.; Zhang, Y.; Harris, H.G.; Fan, M. Catalytic CO2 reforming of
CH4 over Cr-promoted Ni/char for H2 production. Int. J. Hydrog. Energy 2014, 39, 10141–10153,
59. da Silva, A.L.M.; den Breejen, J.P.; Mattos, L.V.; Bitter, J.H.; de Jong, K.P.; Noronha, F.B. Cobalt particle size
effects on catalytic performance for ethanol steam reforming—Smaller is better. J. Catal. 2014, 318, 67–74,
60. Ma, H.; Zeng, L.; Tian, H.; Li, D.; Wang, X.; Li, X.; Gong, J. Efficient hydrogen production from ethanol
steam reforming over La-modified ordered mesoporous Ni-based catalysts. Appl. Catal. B Environ. 2016,
181, 321–331, doi:10.1016/j.apcatb.2015.08.019.
61. Hu, X.; Dong, D.; Shao, X.; Zhang, L.; Lu, G. Steam reforming of acetic acid over cobalt catalysts: Effects of
Zr, Mg and K addition. Int. J. Hydrog. Energy 2017, 42, 4793–4803, doi:10.1016/j.ijhydene.2016.12.033.
62. Biswas, P.; Kunzru, D. Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with
copper, cobalt and calcium. Catal. Lett. 2007, 118, 36–49, doi:10.1007/s10562-007-9133-6.
63. Thaicharoensutcharittham, S.; Meeyoo, V.; Kitiyanan, B.; Rangsunvigit, P.; Rirksomboon, T. Hydrogen
production by steam reforming of acetic acid over Ni-based catalysts. Catal. Today 2011, 164, 257–261,
64. Wang, Y.; Chen, M.; Liang, T.; Yang, Z.; Yang, J.; Liu, S. Hydrogen Generation from Catalytic Steam
Reforming of Acetic Acid by Ni/Attapulgite Catalysts. Catalysts 2016, 6, 172.
65. Nogueira, F.G.E.; Assaf, P.G.M.; Carvalho, H.W.P.; Assaf, E.M. Catalytic steam reforming of acetic acid as
a model compound of bio-oil. Appl. Catal. B Environ. 2014, 160–161, 188–199,
66. Valle, B.; Aramburu, B.; Benito, P.L.; Bilbao, J.; Gayubo, A.G. Biomass to hydrogen-rich gas via steam
reforming of raw bio-oil over Ni/La2O3-αAl2O3 catalyst: Effect of space-time and steam-to-carbon ratio. Fuel
2018, 216, 445–455, doi:10.1016/j.fuel.2017.11.151.
67. Chen, J.; Yang, X.; Li, Y. Investigation on the structure and the oxidation activity of the solid carbon
produced from catalytic decomposition of methane. Fuel 2010, 89, 943–948, doi:10.1016/j.fuel.2009.08.017.
68. Nagasawa, S.; Yudasaka, M.; Hirahara, K.; Ichihashi, T.; Iijima, S. Effect of oxidation on single-wall carbon
nanotubes. Chem. Phys. Lett. 2000, 328, 374–380, doi:10.1016/S0009-2614(00)00960-X.
69. Choong, C.K.S.; Zhong, Z.; Huang, L.; Wang, Z.; Ang, T.P.; Borgna, A.; Lin, J.; Hong, L.; Chen, L. Effect of
calcium addition on catalytic ethanol steam reforming of Ni/Al2O3: I. Catalytic stability, electronic
properties and coking mechanism. Appl. Catal. A Gen. 2011, 407, 145–154, doi:10.1016/j.apcata.2011.08.037.
70. Galetti, A.E.; Gomez, M.F.; Arrúa, L.A.; Abello, M.C. Hydrogen production by ethanol reforming over
NiZnAl catalysts: Influence of Ce addition on carbon deposition. Appl. Catal. A Gen. 2008, 348, 94–102,
71. Natesakhawat, S.; Watson, R.B.; Wang, X.; Ozkan, U.S. Deactivation characteristics of lanthanide-promoted
sol–gel Ni/Al2O3 catalysts in propane steam reforming. J. Catal. 2005, 234, 496–508,
72. Qi, W.; Chen, S.; Wu, Y.; Xie, K. A chromium oxide coated nickel/yttria stabilized zirconia electrode with a
heterojunction interface for use in electrochemical methane reforming. RSC Adv. 2015, 5, 47599–47608,
73. Garcia, L.A.; French, R.; Czernik, S.; Chornet, E. Catalytic steam reforming of bio-oils for the production of
hydrogen: Effects of catalyst composition. Appl. Catal. A Gen. 2000, 201, 225–239, doi:10.1016/S0926-
74. Helveg, S.; Sehested, J.; Rostrup-Nielsen, J.R. Whisker carbon in perspective. Catal. Today 2011, 178, 42–46,
75. Natesakhawat, S.; Wang, X.; Zhang, L.; Ozkan, U.S. Development of chromium-free iron-based catalysts
for high-temperature water-gas shift reaction. J. Mol. Catal. A Chem. 2006, 260, 82–94,
Catalysts 2019, 9, 1013 20 of 20
76. Sierra Gallego, G.; Mondragón, F.; Tatibouët, J.-M.; Barrault, J.; Batiot-Dupeyrat, C. Carbon dioxide
reforming of methane over La
as catalyst precursor—Characterization of carbon deposition. Catal.
Today 2008, 133–135, 200–209, doi:10.1016/j.cattod.2007.12.075.
77. Carrero, A.; Calles, J.A.; Vizcaíno, A.J. Effect of Mg and Ca addition on coke deposition over Cu–Ni/SiO
catalysts for ethanol steam reforming. Chem. Eng. J. 2010, 163, 395–402, doi:10.1016/j.cej.2010.07.029.
78. Montero, C.; Ochoa, A.; Castaño, P.; Bilbao, J.; Gayubo, A.G. Monitoring Ni0 and coke evolution during
the deactivation of a Ni/La
catalyst in ethanol steam reforming in a fluidized bed. J. Catal. 2015,
331, 181–192, doi:10.1016/j.jcat.2015.08.005.
79. Osorio-Vargas, P.; Flores-González, N.A.; Navarro, R.M.; Fierro, J.L.G.; Campos, C.H.; Reyes, P. Improved
stability of Ni/Al
catalysts by effect of promoters (La
, CeO
) for ethanol steam-reforming reaction.
Catal. Today 2016, 259, 27–38, doi:10.1016/j.cattod.2015.04.037.
80. Charisiou, N.D.; Siakavelas, G.; Papageridis, K.N.; Baklavaridis, A.; Tzounis, L.; Polychronopoulou, K.;
Goula, M.A. Hydrogen production via the glycerol steam reforming reaction over nickel supported on
alumina and lanthana-alumina catalysts. Int. J. Hydrog. Energy 2017, 42, 13039–13060,
81. Silva, K.C.; Corio, P.; Santos, J.J. Characterization of the chemical interaction between single-walled carbon
nanotubes and titanium dioxide nanoparticles by thermogravimetric analyses and resonance Raman
spectroscopy. Vib. Spectrosc. 2016, 86, 103–108, doi:10.1016/j.vibspec.2016.06.012.
82. Tzounis, L.; Kirsten, M.; Simon, F.; Mäder, E.; Stamm, M. The interphase microstructure and electrical
properties of glass fibers covalently and non-covalently bonded with multiwall carbon nanotubes. Carbon
2014, 73, 310–324, doi:10.1016/j.carbon.2014.02.069.
83. Ferencz, Z.; Varga, E.; Puskás, R.; Kónya, Z.; Baán, K.; Oszkó, A.; Erdőhelyi, A. Reforming of ethanol on
catalysts reduced at different temperatures. J. Catal. 2018, 358, 118–130,
84. Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G.H.; Chmelka, B.F.; Stucky, G.D. Triblock copolymer
syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279, 548–552,
85. Vizcaíno, A.J.; Carrero, A.; Calles, J.A. Ethanol steam reforming on Mg- and Ca-modified Cu–Ni/SBA-15
catalysts. Catal. Today 2009, 146, 63–70, doi:10.1016/j.cattod.2008.11.020.
86. Carrero, A.; Calles, J.A.; Vizcaíno, A.J. Hydrogen production by ethanol steam reforming over Cu-Ni/SBA-
15 supported catalysts prepared by direct synthesis and impregnation. Appl. Catal. A Gen. 2007, 327, 82–94,
87. Vizcaíno, A.J.; Carrero, A.; Calles, J.A. Comparison of ethanol steam reforming using Co and Ni catalysts
supported on SBA-15 modified by Ca and Mg. Fuel Process. Technol. 2016, 146, 99–109,
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (
... Examples include the addition of an alkali or alkaline earth metals, often in high surface area supports, such as Al2O3, in order to combine with adjacent catalytically active metal sites for SR [122,123]. As CaO has good chemical and thermodynamic properties, it is considered an efficient solid sorbent that can aid enhanced activity [63,65,66,84]. A number of research works have also reported that the incorporation of K and La into the support, in small concentrations, can help prevent sintering and the formation of carbon [124]. ...
... This was attributed to the higher reduction temperatures required for their activation. Megía et al. [65,66] also analyzed the effect of Ca addition to Co/SBA-15 in the SR of acetic acid. The authors observed that higher temperatures were necessary to activate the catalysts, which they attributed either to the stronger interaction between the active phase and the support or to the formation of a new Ca-Co compound. ...
... The performance of Co-Cr/SBA-did not differ much in comparison to the performance of Co-Ce/CaSBA-15, but the presence of Cr raises questions about the material's toxicity [132]. Generally, the characteristics of Co-based catalysts are similar to Ni-based systems, however, Co is susceptible to particle agglomeration [65,66,77,84,96]. ...
Full-text available
The present review focuses on the production of renewable hydrogen through the catalytic steam reforming of bio-oil, the liquid product of the fast pyrolysis of biomass. Although in theory the process is capable of producing high yields of hydrogen, in practice, certain technological issues require radical improvements before its commercialization. Herein, we illustrate the fundamental knowledge behind the technology of the steam reforming of bio-oil and critically discuss the major factors influencing the reforming process such as the feedstock composition, the reactor design, the reaction temperature and pressure, the steam to carbon ratio and the hour space velocity. We also emphasize the latest research for the best suited reforming catalysts among the specific groups of noble metal, transition metal, bimetallic and perovskite type catalysts. The effect of the catalyst preparation method and the technological obstacle of catalytic deactivation due to coke deposition, metal sintering, metal oxidation and sulfur poisoning are addressed. Finally, various novel modified steam reforming techniques which are under development are discussed, such as the in-line two-stage pyrolysis and steam reforming, the sorption enhanced steam reforming (SESR) and the chemical looping steam reforming (CLSR). Moreover, we argue that while the majority of research studies examine hydrogen generation using different model compounds, much work must be done to optimally treat the raw or aqueous bio-oil mixtures for efficient practical use. Moreover, further research is also required on the reaction mechanisms and kinetics of the process, as these have not yet been fully understood.
... The catalysts used for CSR included Al2O3 supported with Pt, Pd, Rh, Ru, and Ni [46]; Co/SBA-15 supported with Cu, Ag, Ce, and Cr [47]; and also rice husk silica supported with Ni [34], or as a source for hydroxy-sodalite zeolite [48]. This indicated that rice husk silica has the potential to perform CSR during the pyrolysis and could reduce the amount of acetic acid as observed in this study. ...
Full-text available
Silica with two different sizes i.e. microsilica (MS) and nanosilica (NS) was used as a catalytic support for vanadium (5-15 wt%) in the pyrolysis of pomelo peels. Besides use of pomelo peels (agricultural residues) as a feedstock for the pyrolysis, to contribute to environmental sustainability, rice husk was used as a silica source for obtaining the silica support. From the result, it was found that non-catalytic pyrolysis of pomelo peels gave a bio-oil yield of 33.3 wt%. The catalytic pyrolysis with vanadium-modified silica decreased the bio-oil yields ranging between 27.2-33.1 wt%. This was due to the occurrence of the second reactions generated from the active sites on the catalysts, which leads to the conversion of bio-oil into gas products. For NS catalyst, increasing the amount of vanadium loading directly decreased the bio-oil yields and increased the gas yield. The variation of product phase distribution was not clearly observed for MS catalyst even with various vanadium loadings. In addition, NS catalyst exhibited higher efficiency in reducing the acid content in the bio-oil, and increasing the phenol content. The distinguished properties of the nanoparticles may be the main reason for these phenomena. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (
... Acetic acid oxidative steam reforming reactions were isothermally performed at 500 C and atmospheric pressure in a fixed-bed reactor on a Microactivity-Pro unit described before [17]. Previously, the catalysts were reduced under pure hydrogen according to H 2 -TPR results at 600 C. ...
In this work, the support effect and the La2O3 promotion of Ni-based catalysts on the oxidative steam reforming of acetic acid as bio-oil model compound has been studied. Ni/SBA-15 showed the worst catalytic performance with an acetic acid conversion dropping below 30% at 500 C ascribed to active phase oxidation. In contrast, Ni supported over mesoporous CeO2 (CeO2-m) reached better catalytic performance and lower coke formation due to the higher Ni dispersion and oxygen mobility of the support. On the other hand, La2O3 promotion to SBA-15 and CeO2-m led to even higher Ni dispersion and prevented sintering during the reforming reaction. This effect resulted in an improvement in the catalytic performance for both promoted samples. As a consequence of low Ni crystallite size and high oxygen mobility, Ni/La2O3-CeO2-m reached almost complete conversion (~96%), the highest hydrogen yield (~53%) maintained for 5 h with the lowest coke formation (62.3 mg coke /gcat h).
... profile was similar to the reported reduction profiles of Co3O4 species with more or less significant overlap of the two peaks mentioned above [6,10,19,26,44]. The first reduction peak can be attributed to the reduction of Co 3+ to Co 2+ , while the other one at higher temperature corresponds to the reduction of Co 2+ to Co 0 . ...
Full-text available
The effect of the Co-Cu oxide catalysts composition on their physicochemical properties and performance in the deep oxidation of ethanol was studied. The catalysts with Co:Cu molar ratios of 4:1, 1:1, and 1:4 were obtained by calcination (4 h at 500 °C in air) of the coprecipitated precursors and characterized in detail using powder XRD, Raman spectroscopy, N2 physisorption, H2-TPR, and XPS. The powder XRD and Raman spectroscopy indicated the formation of Co3O4 and CuO mixtures rather than Co-Cu mixed oxides. The CuO promoted the Co3O4 reduction; the Co-Cu catalysts were reduced more easily than the single-component Co and Cu oxides and the main reduction maxima were shifted to lower temperatures with increasing cobalt content in the catalysts. The Co-Cu oxide catalyst with a Co:Cu molar ratio of 4:1 exhibited the best performance in ethanol gas-phase oxidation, showing the lowest T50 (91 °C) and T90(CO2) (159 °C) temperatures needed for 50% ethanol conversion and 90% conversion to CO2, respectively. The excellent catalytic properties of this Co-Cu oxide catalyst were ascribed to the synergistic effect of Co and Cu components. The high activity and selectivity of the Co-Cu catalyst was attributed to the presence of finely dispersed CuO particles on the surface of Co3O4.
... The metal loadings, determined by ICP-AES analysis, were close to the nominal values fixed during the catalyst synthesis. Attending to BET surface area values, SBA-15-based materials achieved the highest values despite this value decreasing when Ni is incorporated into the support during the synthesis step as reported before [30]. Ce-based catalysts, more specifically the CeO2-m sample, exhibit similar BET surfaces and pore volume rates than those described in the literature for similar materials prepared by nanocasting using this template [31,32]. ...
Full-text available
Oxidative steam reforming allows higher energy efficiency and lowers coke deposition compared to traditional steam reforming. In this work, CeO2-based supports have been prepared with Ni as the active phase, and they were tested in the oxidative steam reforming of acetic acid. The influence of the O2/AcOH molar ratio (0-0.3) has been evaluated over Ni/CeO2. The results stated that by increasing oxygen content in the feeding mixture, acetic acid conversion increases, too, with a decrease in coke deposition and hydrogen yield. To have a proper balance between the acetic acid conversion and the hydrogen yield, an O2/AcOH molar ratio of 0.075 was selected to study the catalytic performance of Ni catalysts over different supports: commercial CeO2, a novel mesostructured CeO2, and CeO2-SBA-15. Due to higher Ni dispersion over the support, the mesostructured catalysts allowed higher acetic acid conversion and hydrogen yield compared to the nonporous Ni/CeO2. The best catalytic performance and the lowest coke formation (120.6 mgcoke·gcat-1 ·h-1) were obtained with the mesostructured Ni/CeO2. This sample reached almost complete conversion (>97%) at 500 °C, maintaining the hydrogen yield over 51.5% after 5 h TOS, being close to the predicted value by the thermodynamic equilibrium that is due to the synergistic coordination between Ni and CeO2 particles.
... Most hydrogen is produced via the natural gas reforming processes; however, the biomass gasification and pyrolysis [5] to obtain bio-oil and followed by reforming is growing as a green alternative [6]. Model organic molecules derived from biomass, such as methanol, ethanol [7] or acetic acid [8] have been extensively studied in the last decades as hydrogen sources by pointing out the required improvement of the stability and selectivity of the involved catalytic systems. Water splitting is considered an ideal hydrogen production process as it can potentially substitute conventional fossil fuel-based processes with zero-carbon dioxide emissions [9]. ...
Cover Page
Full-text available
Editorial to the special issue "Catalysts for Sustainable Hydrogen Production: Preparation, Applications and Process Integration"
... The potential of hydrogen as a versatile and clean energy vector is becoming a relevant topic in the last years [1,2] to replace progressively the use of fossil fuels with renewable energies [3,4]. Different studies show the potential of a wide variety of technologies to produce green hydrogen, such as water electrolysis [5], thermochemical water splitting [6], dark fermentation [7], biomass gasification [8], or biomassderivatives reforming [9,10], among others. However, the contribution of all these technologies to hydrogen production is certainly residual due to their elevated and technological early stages [11]. ...
Full-text available
This work addresses the use of TiO2-based particles as an intermediate layer for reaching fully dense Pd-membranes by Electroless Pore-Plating for long-time hydrogen separation. Two different intermediate layers formed by raw and Pd-doped TiO2 particles were considered. The estimated Pd-thickness of the composite membrane was reduced in half when the ceramic particles were doped with Pd nuclei before their incorporation onto the porous support by vacuum-assisted dip-coating. The real thickness of the top Pd-film was even lower (around 3 μm), as evidenced by the cross-section SEM images. However, a certain amount of palladium penetrates in some points of the porous structure of the support up to 50 μm in depth. In this manner, despite saving a noticeable amount of palladium during the membrane fabrication, lower H2-permeance was found while permeating pure hydrogen from the inner to the outer surface of the membrane at 400 °C (3.55·10⁻⁴ against 4.59·10⁻⁴ mol m⁻² s⁻¹ Pa−0.5). Certain concentration-polarization was found in the case of feeding binary H2–N2 mixtures for all the conditions, especially in the case of reaching the porous support before the Pd-film during the permeation process. Similarly, the effect of using sweep gas is more significant when applied on the side where the Pd-film is placed. Besides, both membranes showed good mechanical stability for around 200 h, obtaining a complete H2/N2 ideal separation factor for the entire set of experiments. At this point, this value decreased up to around 400 for the membrane prepared with raw TiO2 particles as intermediate layer (TiO2/Pd). At the same time, complete selectivity was maintained up to 1000 h in case of using doped TiO2 particles (Pd–TiO2/Pd). However, a specific decrease in the H2-permeate flux was found while operating at 450 °C due to a possible alloy between palladium and titanium that is not formed at a lower temperature (400 °C). Therefore, Pd–TiO2/Pd membranes prepared by Electroless Pore-Plating could be very attractive to be used under stable operation in either independent separators or membrane reactors in which moderate temperatures are required.
As a significant by-product of many thermochemical and biological waste conversion processes, acetic acid (AcOH) is often investigated as model feedstock in the production of sustainable hydrogen from non-fossil sources. The kinetics of its steam reforming were extracted from packed bed reactor experiments over an industrially produced 14 wt% Ni/Ca-Al2O3 catalyst at atmospheric pressure. The model consisting of AcOH steam reforming producing CO2 and H2, AcOH decomposition to CO and H2, and water gas shift, achieved the best fit, reflected in the lowest average relative errors (ARE) with experimental results, with ARE values below 5.4% and 6.4% on AcOH and water conversions respectively, and below 4% on H2 mol fraction. This model was validated away from equilibrium using additional experimental points, as well as for a wide range of equilibrium conditions with varying temperature (600–700 °C) and feed molar steam to carbon ratios (3–8) at atmospheric pressure using an independent method.
Full-text available
Dehydrogenation coupling reaction is an efficient strategy of metal-catalyzed organic synthesis, but it is still a research hotspot to regulate the positive effect of various metals on the reaction and make them cooperate with each other. In this work, nanocomposite modified with aluminum and loaded with copper were used as bimetallic catalysts for dehydrogenation coupling reaction. The results showed that the modification of aluminum maked CuO particles disperse highly and exist stably on SBA-15. The bimetallic synergistic catalytic effect of Cu/Al@SBA-15 composite was far greater than that of any one active components alone, and the synergistic effect between Cu and Al was the main reason for its excellent catalytic performance. It guided the dehydrogenation coupling reaction of o-aminophenol and benzyl alcohol, and a series of benzothiazoles products were obtained efficiently by one-pot method. Moreover, the Cu/Al@SBA-15 catalyst still has stable catalytic activity after repeated use, and the leaching of aluminum and copper species in solution was negligible after the reaction. The copper–aluminum bimetal used in strategy does not belong to the highly toxic metal sequence, so this method provides a green synthesis platform for accessing pharmaceutically relevant benzoazoles. Graphical abstract General Scheme. Synthesis of o-aminophenols and benzyl alcohols to benzothiazoles catalyzed by bimetallic synergistic effect of Cu/Al@SBA-15 nanocomposite.
Full-text available
The catalytic activity of M(Ag, Ru, Pt)–Ni/CeO2–SiO2 catalysts prepared by wet impregnation at different M loadings (0–3 wt%) for oxidative steam reforming of ethanol (OSR) was investigated at H2O/C2H5OH = 4, O2/C2H5OH = 0.5, T = 300–600 °C and WHSV = 61.7 h⁻¹. Ag deposition on the Ni/CeO2–SiO2 sample resulted in lower H2 yields, whatever the silver content. Conversely, Ru and Pt addition improved the performances of the monometallic sample and catalyst activity was enhanced by the reduction of metals loading. Similar results were recorded over the catalysts prepared at the same metals content and a metal loading of 0.5 wt% was sufficient to reach the highest performance in the investigated temperature interval. The kinetic model able to predict the experimental results obtained over the most promising formulations includes ethanol decomposition, methane oxidation and steam reforming, water gas shift; Pt as well as Ru addition to the Ni/CeO2–SiO2 sample reduced the activation energy of the involved reactions and Ru was demonstrated to be a valid substitute of the Pt for OSR of ethanol. Thus, by employing smaller noble metal content and less expensive materials, it is possible to reduce the catalyst price. Graphical Abstract Open image in new window
Full-text available
The commercial production of advanced fuels based on bio-oil gasification could be promising because the cost-effective transport of bio-oil could promote large-scale implementation of this biomass technology. So far there has no specialized review of bio-oil gasification processes, including non-catalytic partial oxidation of bio-oil for syngas production and steam gasification of bio-oil for hydrogen production. A detailed and comprehensive review of gasification of bio-oil for gas production is presented in this paper. The background and significance of bio-oil research, the characteristics of bio-oil suitable for gasification, bio-oil gasification theory, types and configurations of bio-oil gasifiers, the quality of the product gas, parameter effects, and economic evaluation of bio-oil gasification are discussed, and finally a summary and future outlook is also delivered. Particular emphasis is placed to on the discussion regarding the atomization of bio-oil, entrained flow gasifiers and their advantages, gas composition and the economic feasibility of production of advanced fuels via bio-oil gasification. Challenges for the future are identified as (1) make full use of the experience accumulated in the area of petroleum refining; (2) practical demonstration of bio-oil gasification on a scale of 500 to 1000 kg bio-oil per hour; (3) the development of mathematical models for bio-oil gasification systems; and (4) development of suitable catalysts and profoundly understand the catalysts deactivation mechanism at different stages for steam gasification of bio-oil.
Full-text available
Titanium silicalite (TS) and TiO2 nanocomposites were prepared by mixing TS and TiO2 with different ratios in ethanol. They were impregnated with 15 wt% Co loading to afford Co‐based catalysts. Fischer–Tropsch synthesis (FTS) performance of these TS–TiO2 nanocomposite‐supported Co‐based catalysts was studied in a fixed‐bed tubular reactor. The results reveal that the Co/TS–TiO2 catalysts have better catalytic performance than Co/TS or Co/TiO2 each with a single support, showing the synergistic effect of the binary TS–TiO2 support. Among the TS–TiO2 nanocomposite‐supported Co‐based catalysts, Co/TS–TiO2‐1 presents the highest activity. These catalysts were characterized using N2 adsorption–desorption measurements, X‐ray diffraction, X‐ray photoelectron spectroscopy, H2 temperature‐programmed reduction, H2 temperature‐programmed desorption and transmission electron microscopy. It was found that the position of the active component has a significant effect on the catalytic activity. In the TS–TiO2 nanocomposites, cobalt oxides located at the new pores developed between TS and TiO2 can exhibit better catalytic activity. Also, a positive relationship is observed between Co dispersion and FTS catalytic performance for all catalysts. The catalytic activity is improved on increasing the dispersion of Co. Co/TS–TiO2 catalysts with binary TS–TiO2 support have better catalytic performance than Co/TS or Co/TiO2 with single supports, showing the synergistic effect of TS and TiO2 of the binary support.
Full-text available
Hydrogen obtained from biomass derivatives is considered a promising alternative to fossil fuels. The aim of this work is to test the viability of Ni-M/SBA-15 (M: Co, Cu, Cr) catalysts for the hydrogen production from bio-oil aqueous fraction reforming. Tests were performed in a fixed-bed reactor at 600 °C and atmospheric pressure. Firstly, the steam reforming (SR) of acetic acid, hydroxyacetone, furfural and phenol, as representative constituents of the bio-oil aqueous fraction, was carried out. Lower reactivity with increasing carbon number and decreasing steam-to-carbon ratio was observed. Coking rate during SR is a consequence of carbon number and aromaticity of the reactant, as well as the steam-to-carbon ratio. However, deactivation also depends on the graphitization degree of carbon filaments, higher in the case of coke formed from phenol. Then, the performance of the Ni-M/SBA-15 catalysts was studied in the reforming of a bio-oil aqueous fraction surrogate containing the four model compounds. Ni-Co/SBA-15 and Ni-Cr/SBA-15 samples were the most active because Co also catalyze the steam reforming reactions and Cr promotes the formation of very small Ni crystallites accounting for high conversion and the low coke deposition (~8 times lower than Ni/SBA-15) in the form of poorly condensed carbon filaments.
In this study, novel carbon-oxide composite-supported Ni, Co and Fe catalysts were prepared by the sol-gel method using polyethylene glycol (PEG) as a carbon source and catalytic properties of the test catalysts were estimated for the steam reforming reactions of ethanol. The reactions were carried out in a fixed bed reactor under the following conditions: H2O/EtOH (mol/mol) = 12, and temperatures 300 °C-600 °C. Nitrogen adsorption and desorption, XRD, XRF and TG-DTA were measured for the characterization of the catalysts. When carbon from PEG was not used, both conversion of ethanol and hydrogen yield decreased. When the conversion and the hydrogen yield were compared between catalysts calcined at 500 °C, Ni catalysts showed the higher conversions and hydrogen yields than Co catalysts. When Co catalysts were calcined at 700 °C, comparable activity and the higher hydrogen yield were observed in the reaction at 600 °C. The composite-supported 16Co63C21A, calcined at 700 °C under N2 atmosphere, facilitated the highest activity and hydrogen yield among the Co catalysts: the hydrogen yield reached 80% when the conversion of ethanol was 100% at 600 °C. Only Co metal was detected for the fresh Co catalysts calcined at 700 °C while both CoO and Co3O4 peaks were detected for catalysts calcined at 500 °C.
Hydrogen production by stream reforming ethanol (SRE) derived from biomass is a promising method. Thus, utilizing cut-price mineral clays to exploit an efficient and stable catalyst is of great significance. In this work, attapulgite (ATP)-supported nickel species catalysts with different Ni contents (denoted as xNi/ATP, x = 5–40 wt%) are manufactured by conventional and home precipitation methods. Many tests such as N2 adsorption-desorption, XRD, TEM, H2-TPR and XPS are utilized to characterize the structural and surface properties of as-prepared catalysts. It is found that the metal-support interaction and reducibility of xNi/ATP catalysts presented volcano-shaped trends in terms of Ni content, and the Ni-O-Si/Al species formed through the interplay of nickel species with the ATP framework play a key role in determining catalytic performance. The superior balance of Ni-O-Si/Al species in the 20Ni/ATP catalyst gave it the highest reductive degree and metal-support interaction. Consequently, 20Ni/ATP exhibited the uppermost hydrogen production and ethanol conversion and the most catalytic stability during the SRE reaction. In addition, the conversion and H2 yield obviously decreased with the weight hourly space velocity (WHSV, h⁻¹), whereas they presented volcanic-type curves with increasing steam/carbon (S/C) molar ratios during SRE.
Four samples of Zn-hydrotalcite containing different amounts of Co (5, 10, 20, and 30 wt%) have been synthesized and tested in the steam reforming of ethanol. The best results were obtained with the sample containing 20 wt% of Co (20CoHT), with a complete conversion of ethanol and yields to hydrogen close to the equilibrium (73 mol.%). The physicochemical characterization of the samples by DRX, BET area and TPR indicates that the excellent performance exhibited by the sample containing 20 wt% of Co is due to the higher percentage of reduced cobalt and lower crystallite size of metallic cobalt present in this sample (11 nm). Additional studies have been carried out to improve the stability of this catalytic material against deactivation by the incorporation of 1 wt% of La. Stability studies were carried out using an industrial alcoholic waste as feed. Deactivation after 24 h of reaction time was found lower for the catalyst containing La (20CoLaHT), confirming the positive effect of lanthanum on the catalytic stability. The results presented here show that it is possible to prepare a catalyst based on Co supported on Zn-hydrotalcite and promoted with La with improved ethanol conversion, high hydrogen selectivity, and high stability to produce hydrogen by the steam reforming of an industrial alcoholic waste without commercial value.
In recent times, glycerol has been employed as feedstock for the production of syngas (H2 and CO) with H2 as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al2O3 catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L gcat⁻¹ h⁻¹). Ag (3)-Ni/Al2O3 gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H2 production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al2O3, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O2.