[Show abstract][Hide abstract] ABSTRACT: Low-temperature catalytic decarboxylation was studied for continuous treatment of model wastewaters containing acetic and formic acid. A three-phase trickle-bed reactor was operated at Tr=75–240 °C, PN2=10 bar, ΦG=50 NmL/min and ΦL=0.5 mL/min. Before and after reaction, 3 wt. % Ru/TiO2 catalyst was thoroughly characterized (N2 physisorption, XRD, TPO, H2-TPR, CHNS, DRIFTS). CH3COOH decarboxylation at sufficiently high temperatures (T>225 °C) resulted in higher than 80 % selectivity for CH4 and CO2, stable catalyst activity and no accumulation of carbonaceous deposits. Low selectivity for H2 and CO2 (<60 %) was achieved during HCOOH decarboxylation, with simultaneous occurrence of CO and CO2 methanation reactions, as well as coke accumulation resulting in catalyst deactivation.
[Show abstract][Hide abstract] ABSTRACT: In this study, photocatalytic and catalytic wet-air oxidation (CWAO) processes were used to examine removal efficiency of bisphenol A from aqueous samples over several titanate nanotube-based catalysts. Unexpected toxicity of treated bisphenol A (BPA) samples by means of CWAO process to some tested species was determined. In addition, the CWAO effluent was recycled 5 or 10-fold in order to increase the number of interactions between the liquid phase and catalyst. Consequently, the ICP-MS analysis indicated higher concentrations of some toxic metals like chromium, nickel, molybdenum, silver, and zinc in the recycled samples in comparison to both single-pass sample and photocatalytically treated solution. The highest toxicity of 5- and 10-fold recycled solutions in CWAO process was observed to water fleas, which could be correlated to high concentrations of chromium, nickel, and silver detected in tested samples. The obtained results clearly demonstrated that aqueous samples treated by means of advanced oxidation processes should always be analyzed using (i) chemical analyses to assess removal of BPA and total organic carbon from treated aqueous samples as well as (ii) a battery of aquatic organisms from different taxonomic groups to determine possible toxicity.
[Show abstract][Hide abstract] ABSTRACT: To attain sustained activity and stability in CH4-CO2 dry reforming (CCDR), two nanocomposite materials comprising silicon carbide or alumina and ceria-zirconia were introduced to support cobalt-nickel (CoNi) catalysts. Following the sequential impregnation-ultrasonication-deposition precipitation procedure, catalysts were systematically characterized and their performances were tested at 1.2 bar and 750 oC, where undiluted CH4-CO2 (ratio = 1: 1) streams simulating biogas and the real industrial conditions were fed into a continuous flow reactor. For CCDR reactions conducted at WHSV = 12 L/(gcat∙h), good activity and stability were shown for both catalysts. Carbon content as low as 0.3 wt. % and high conversions (70-78 % and 78-88 % for CH4 and CO2, respectively) were recorded over 23 h and 550 h tests. Interestingly, by increasing the WHSV value to an order of magnitude higher, i.e., at 120 L/(gcat∙h) with all other conditions held constant, a 6 h short-term test showed remarkably high conversions near equilibrium values, implying that the reactions still occurred within the thermodynamic regime despite a reduced ten-fold mass of catalyst bed. This infers that not all active sites available on the catalyst surface were fully exploited. Compared to previous catalyst performances, the progress made in this work is ascribed to the synergistic effects from selected support materials that contributed remarkable redox properties, high surface area, mechanical and thermal stability to the catalysts.
[Show abstract][Hide abstract] ABSTRACT: This study investigates how morphology, active metal content and oxygen storage capacity of various bimetallic NiCo/CeZrO2 materials influence their catalytic activity and stability in the methane dry reforming reaction. Catalyst preparation procedure and chemical composition were steered to finally obtain materials, which do not accumulate carbon during the CH4/CO2 reforming reaction. Oxygen storage capacity of the CeZrO2 catalyst support was identified to play a vital role in retarding carbon accumulation over the tested NiCo/CeZrO2 materials. This property can be fully developed when a nanocrystalline solid solution of CeO2 and ZrO2 is formed. Secondly, a high dispersion of nickel and cobalt is crucial for two reasons: (i) catalysts which contain larger NiCo bimetallic particles (for example with 12–18 wt.% active metal loading) exhibit a low metal-support interphase that results in enhanced coke formation rates; (ii) additionally, only a marginal gain in methane reforming rates are achieved at higher loadings, compared to catalysts with a 3–6 wt.% active metal content. We demonstrated that a NiCo/CeZrO2 catalyst under relevant operating conditions after 400 h TOS maintains 79 and 84% conversion of CH4 and CO2, with negligible coke accumulation.
[Show abstract][Hide abstract] ABSTRACT: Mesoporous zirconia and nickel incorporated zirconia catalysts were prepared following different routes. Synthesis of mesoporous zirconia and Ni incorporated zirconia with very narrow pore size distributions and high surface area was achieved. Ni incorporated mesoporous zirconia materials showed high activity in carbon dioxide reforming of methane, performed at 600 °C. Coke formation during dry reforming was eliminated over the Ni incorporated zirconia catalyst prepared by the one-pot procedure, using Pluronic P123 as the surfactant. It was shown that Ni was very well distributed within this material with cluster sizes smaller than the detection limit of XRD. This catalyst also showed highly stable catalytic performance. However, the catalysts prepared by the impregnation method showed higher activity but much higher coke formation than the catalyst prepared by the one-pot route.
International Journal of Hydrogen Energy 03/2015; 40(8). DOI:10.1016/j.ijhydene.2015.01.023 · 2.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study explores CeZrO2 deposited over commercial β-SiC, and a highly ordered 3D β-SiC synthesised in the laboratory via electrophoretic deposition, as well as γ-Al2O3 in order to prepare three types of dual support for NiCo bimetallic catalyst in CH4-CO2 dry reforming (DR). CeZrO2 was deposited over γ-Al2O3 and β-SiC by dry impregnation (DI), wet impregnation (WI) and 2-step deposition precipitation (DP). XRD analysis indicated that the constituents of the dual supports were retained after calcination, as well as before and after the DR reaction. CeZrO2 remained as a mixed oxide solid solution, whilst alumina formed spinel structures with Ni and Co before the catalysts were reduced in H2 during the pretreatment step prior to the activity tests. During 550 h stability tests, WI, 2-step SICAT/CeZrO2 and 2-step γ-Al2O3/CeZrO2 solids were identified as the most promising catalysts, maintaining high DR activities without deactivation. Notably, 2-step SiC(SICAT) and 2-step γ-Al2O3/CeZrO2 samples recorded the highest yield (H2 = 77%, CO = 90%; H2 = 71%, CO = 81%), with a coke content of 7.7 and 0.6 wt.%, respectively. Carbon deposition for the former is high; contrarily, for WI SiC(SICAT) solid, it accumulated a lower amount of 2.6 wt.%. No agglomeration of CeZrO2 and NiCo phases was observed, evidencing excellent robustness and thermal resistance of these dual supports.
[Show abstract][Hide abstract] ABSTRACT: The effect of nanomaterials on biota under realistic environmental conditions is an important question. However, there is still a lack of knowledge on how different illumination conditions alter the toxicity of some photocatalytic nanomaterials. We have investigated how environmentally relevant UV-A exposure (intensity 8.50 +/- 0.61 W/m(2), exposure dose 9.0 J/cm(2)) affected the toxicity of cerium oxide (CeO2)-based nanostructured materials to the early-life stages of zebrafish Danio rerio. Pure cerium oxide (CeO2), copper-cerium (CuO-CeO2) (with a nominal 10,15 and 20 mol.% CuO content), cerium-zirconium (CeO2-ZrO2) and nickel and cobalt (Ni-Co) deposited over CeO2-ZrO2 were tested. It was found that under both illumination regimes, none of the tested materials affected the normal development or induced mortality of zebrafish early-life stages up to 100 mg/L. Only in the case of CuO-CeO2, the growth of larvae was decreased (96 h LOEC values for CuCe10, CuCe15 and CuCe20 were 50, 50 and 10 mg/L, respectively). To conclude, CeO2-based nanostructured materials are not severely toxic to zebrafish and environmentally relevant UV-A exposure does not enhance their toxicity.
Science of The Total Environment 02/2015; 506. DOI:10.1016/j.scitotenv.2014.10.120 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dry reforming of methane with CO2 was investigated over bi-metallic W and Ni incorporated mesoporous alumina catalysts prepared by the one-pot sol-gel route. Powdered materials were thoroughly characterized (N2-physisorption, XRD, XPS, SEM-EDX, TGA-DTA, TPH) prior and post catalytic runs, performed at 600 and 750 oC. High surface area W-Ni incorporated mesoporous alumina catalysts (SBET=178-192 m2/g) synthesized in this work showed excellent performance for the conversion of model biogas to synthesis gas. The Ni-W containing materials exhibited high catalytic activity, which was maintained throughout 150 hours TOS long-term operation at 750 oC. Increase of the W loading (0-10-15 wt. %) at fixed nickel amount (5 wt. %) resulted in prevented deactivation of the catalyst, most prominent at 600 °C, and minimization of coke formation on the surface of the catalyst. Tungsten incorporation was thus proven to significantly enhance and stabilize the overall catalyst performance.
[Show abstract][Hide abstract] ABSTRACT: Different chemical modifications were performed to the natural aluminosilicate Montanit300® in order to improve its catalytic activity in PE depolymerization. Performance of such prepared catalysts was compared to established solid acid catalysts, such as HZSM-5, sulfonated and fluorinated γ-Al2O3 and amorphous silica–alumina. Pyridine TG and DRIFTS characterization revealed mild acid treatment and aluminum grafting as successful in increasing acid site density through impurity removal and specific surface area increase. Mesoporous catalyst structure that allows facile diffusion through its pore network, together with high-density Brønsted acid sites, was found to be crucial to obtain high catalytic activity. The T50 value for PE depolymerization was lowered by 162 °C with sulfonated γ-Al2O3 solid, compared to non-catalyzed reaction, whereas with aluminum-grafted Montanit300® catalyst this value was lowered by 65 °C. PE depolymerization products present in the condensed liquid phase using aluminum-grafted Montanit300® catalyst were exclusively alkanes with chain length up to 21 carbon atoms. Liquid, coke and gas yields were found to be 53, 0.4 and 46.6%, respectively, the latter consisting of linear and branched C2–C4 alkenes and alkanes.
[Show abstract][Hide abstract] ABSTRACT: High surface area CeO2 nanospheres as an active catalyst support were synthesized using glycothermal approach. Different loadings of copper (4, 6, 10 and 15 wt.%) were supported by wet impregnation method. Prepared materials were characterized by means of TEM, SEM-EDX, XRD, UV-Vis diffuse reflectance, N2 adsorption/desorption, DRIFT and H2-TPR techniques, and tested for the catalytic reaction of nitrous oxide decomposition. The best activity in the N2O degradation was found for the sample containing 10 wt.% of Cu that can be attributed to the highest number of small CuO clusters on the catalyst surface. Further increase of copper content strongly affects the dispersion and leads to the formation of less active segregated CuO phase, which was confirmed by XRD, UV-Vis and H2-TPR results. Accordingly to UV–Vis examination and DRIFT analysis using CO as a probe molecule, all solids contain Cu+1 ions which play a crucial role in the N2O decomposition mechanism. The synthesized catalysts were also tested in wet or NO containing atmospheres, where an inhibiting effect takes place and leads to shifting of conversion profiles to higher temperature by 65 and 10 °C, correspondingly. It was found out that the formation of a new, crystalline CuO·3H2O phase occurs in water vapour containing atmosphere, which can result in catalyst deactivation. However, this effect is fully reversible and the catalyst is able to replenish initial activity in dry atmosphere. Potentiality of CuO/CeO2 materials in catalytic N2O decomposition in industrial processes was confirmed by long-term stability tests performed in the period of 50 h in the presence of inhibiting gas components.
[Show abstract][Hide abstract] ABSTRACT: Abstract In this study, we report a simple synthesis procedure of anatase/rutile/brookite TiO2 nanocomposite material, designed for efficient transformation of emerging water pollutants (e.g. bisphenol A) to CO2 and H2O as final products of complete photo-oxidation. Sol-gel procedure with a subsequent hydrothermal treatment carried out at mild temperature and in the presence of 3 M HCl led to the formation of TiO2 nanomaterial, which consists of anatase (43 %), rutile (24 %) and brookite (33 %) polymorph phases within the same material. For the purpose of efficient evaluation of nanocomposite activity, individual polymorphs of anatase, rutile and brookite were also prepared using the same precursor material. Individual polymorph phases within the nanocomposite material crystallized separately and formed mixed agglomerates; the polymorphs were regularly shaped and randomly distributed in agglomerates, where some of the anatase particles exhibited truncated octahedron morphology, rutile was in the form of tetragonal prisms with pyramidal termination and brookite was shaped as blocky particles, which were found to be the smallest within the nanocomposite material (∼ 20 nm). Newly synthesized TiO2 nanocomposite was highly active in terms of mineralization, since after 60 min of irradiation under UV light almost 60 % of water dissolved pollutant bisphenol A was successfully transformed into CO2 in H2O. On the other hand, the benchmark TiO2 P25 Degussa catalyst reached a lower extent of mineralization, which is due to significantly less expressed resistance to accumulation of carbonaceous deposits on the catalyst surface.
Applied Catalysis B Environmental 01/2015; DOI:10.1016/j.apcatb.2015.08.027 · 6.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Zinc(II) oxide nanoparticles were used for the stabilization of dicyclopentadiene (DCPD)−water-based high internal phase emulsions (HIPEs), which were subsequently cured using ring-opening metathesis polymerization (ROMP). The morphology of the resulting ZnO- pDCPD nanocomposite foams was investigated in correlation to the nanoparticle loading and nanoparticle surface chemistry. While hydrophilic ZnO nanoparticles were found to be unsuitable for stabilizing the HIPE, oleic acid coated, yet hydrophobic, ZnO nanoparticles were effectiv HIPE stabilizers, yielding polymer foams with ZnO nanoparticles located predominately at their surface. These inorganic/organic hybrid foam-materials were subsequently calcined at 550 °C for 15 min to obtain inorganic macroporous ZnO foams with a morphology reminiscent to the original hybrid foam, and a specific surface area of 1.5 m2 g−1. Longer calcination time (550 °C, 15h) resulted in a sea urchin like morphology of the ZnO foams, characterized by higher specific surface area of 5.5 m2 g−1. The latter foam type showed an appealing catalytic performance in the catalytic wet air oxidation (CWAO) process for the destruction of bisphenol A.
[Show abstract][Hide abstract] ABSTRACT: Ordered mesoporous CuO-CeO2 mixed oxides with different Cu loadings were synthesized by means of hard template replication approach using mesoporous silica KIT-6 as a template. Prepared materials were characterized by SEM-EDX, XRD, UV-Vis DR, N-2 adsorption/desorption, and H-2-TPR techniques. The catalytic decomposition of N2O was studied in a fixed-bed reactor in the temperature range from 300 degrees C to 600 degrees C and GHSV = 45,000 h(-1). Solids prepared by replication approach showed superior catalytic activity in comparison to materials synthesized by conventional preparation methods. Among the solids tested, the highest conversion of N2O was observed in the presence of a catalyst containing 40 mol.% Cu. Reduction of prepared samples occurs at much lower temperatures in comparison to individual CuO and CeO2 oxides due to synergetic effect present in mixed oxides. N2O decomposition tests revealed very good agreement between the catalytic activity and material reducibility, which increased with increasing Cu content from 25 to 40 mol.%. Formation of segregated CuO phase was observed for samples with Cu content above 40 mol.%. Accordingly to UV-Vis examination, all solids contain Cu+1 and Ce+3, which play a crucial role in the N2O decomposition mechanism. In wet (1.5 vol.% H2O) or NO (1.5 vol.%) containing atmospheres, where inhibiting effect due to competitive adsorption of water and NO molecules on active sites takes place, resulting conversion profiles were shifted to higher temperature by 70 degrees C and 25 degrees C, respectively. Results of long-term stability test performed in the period of 50 h confirmed good catalytic stability of an investigated material, which can be attributed to catalyst ability to regenerate active sites by desorption of formed oxygen from the catalyst surface.
Chemical Engineering Journal 10/2014; 254:153–162. DOI:10.1016/j.cej.2014.05.127 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Complex waste streams originating from extraction processes containing residual
organic solvents and increased C/N ratios have not yet been considered as feedstock for
biogas production to a great extent. In this study, spent rosehip (Rosa canina L.) solid
residue (64 % VS, 22 MJ/kg HHV, 30C/1N) was obtained from an industrial ethanol
aided extraction process, and extensively examined in an automated batch bioreactor
system for biogas production. Fraction separation of the compact lignocellulosic seeds
increased the available sugar and ethanol content, resulting in high biogas potential of
the sieved residue (516 NL/kg VS’). In co-digestion of spent rosehip substrate with nondeactivated
nitrogen rich microbial co-substrates, methanogenesis was favored (Ym>68
%CH4). In individual digestion of microbial co-substrates, this was not the case, as biogas
with 28 vol. % N2 was produced from activated sludge supplement. Therefore, effective
inhibition of exogenous microbiota was achieved in the presence of carbonaceous spent
[Show abstract][Hide abstract] ABSTRACT: To improve the activity of nickel-cobalt (NiCo) catalyst supported on ceria-zirconia (CeZr) in the dry reforming of methane (DRM) with carbon dioxide, and to lower the coking rate in this process, 1.5 wt.% and 2.5 wt.% NiCo catalysts were prepared using two approaches, i.e. freeze-drying (FD) and NO calcination for comparison against oven-drying (OD) and air calcination (air), respectively. Their impact was studied for 20 h of DRM at 750 degrees C and 1.2 bar, with undiluted CH4-CO2 feed simulating the real conditions. NO-calcined samples show, on average, more pronounced improvement through increased conversion of CH4 (90%), followed by FD samples (85%) from the air and OD-prepared samples (both 82%). Coking content varied between 0.67 and 0.82 wt.%. The observed slow catalyst deactivation might be caused by sintering of the catalysts. Higher quantity of CO than H-2 for syngas production was obtained, owing to concurrent reverse water-gas shift side reaction, and high redox properties of the defective CeZr lattice that enabled surface carbon gasification by continuous replenishment of oxygen from the support to produce CO, of which the latter phenomenon also explains the low carbon deposition. H-2/CO ratio between 0.42 and 0.85 was achieved, with FD and NO samples fared better (0.83-0.85) over the ones prepared by conventional methods (0.73-0.82) for 2.5%NiCo loaded catalysts. Copyright
International Journal of Hydrogen Energy 08/2014; 39(24):12636–12647. DOI:10.1016/j.ijhydene.2014.06.083 · 2.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this contribution, a compact reactor system is presented that enables efficient processing of grey water in order to facilitate its reutilization for flushing toilet bowls. The treatment of collected grey water is performed in combination with an aerobic/anoxic biological process carried out in a submersed bioreactor with immobilized biomass for the removal of dissolved organic substances, and a procedure of adjusting the concentration of microorganisms in the liquid phase by using a simple technique of flow-through ultraviolet-light based disinfection. In this system which operates at ambient temperature as a semi-continuous recycle reactor, significant removal of organic matter was achieved (conversions up to 65%, expressed as total organic carbon) without the occurrence of malodour. A low concentration of dispersed microorganisms was measured in treated grey water; importantly, no coliforms were accumulated in the unit.
Water Science & Technology Water Supply 08/2014; 14(4):626. DOI:10.2166/ws.2014.018
[Show abstract][Hide abstract] ABSTRACT: The paper presents the development, validation, and evaluation of measurement uncertainty of a method for quantitative determination of essential and nonessential elements in medicinal plants and their aqueous extracts by using inductively coupled plasma optical emission spectrometry.
The detailed validation of the analytical procedure and calculation of the measurement uncertainty budget allowed the recognition of the methods' critical points.
The obtained limit of quantification, repeatability, and measurement uncertainty were satisfactory. The trueness of the method was verified by recovery estimation using certified reference materials. The recovery rates of all metals were between 95% and 105%.
The paper presents for the first time all the steps needed to evaluate the measurement uncertainty and validate the determination method of selected elements in medicinal plants and their aqueous extracts. In summary, the obtained results demonstrate that the method can be applied effectively for the designed purpose.
[Show abstract][Hide abstract] ABSTRACT: Ceria-zirconia mixed oxides (CeZr) were glycol-thermally synthesised as nano-crystalline supports with tunable ratios for the anchoring of nickel-cobalt (Ni-Co) catalyst to enhance methane dry reforming (MDR) reaction with carbon dioxide. High conversion of methane (90%) and carbon dioxide (92%), good output (H-2 = 32%; CO = 44%), and selectivity and stability of syngas prove the effectiveness of the catalyst deposited on this support. 80:20 for Ce:Zr was identified as the optimal ratio to attain active and stable catalytic performance in MDR, with a low coking content of 0.47 wt.%.