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5 results on '"Low-temperature water-gas shift"'

1. Dispersion of copper on ceria for the low-temperature water-gas shift reaction.

Author

Ning, Jing, Zhou, Yan, Chen, Aling, Li, Yong, Miao, Shu, and Shen, Wenjie

Subjects
*WATER gas shift reactions, *COPPER, *COPPER clusters, *CLUSTERING of particles, *DISPERSION (Chemistry), *WATER-gas
Abstract

• Copper dispersion on a rod-shaped ceria was examined with respect to copper loading. • Monolayer and bilayer copper clusters were dominate at copper loading of less than 15 mol.%. • Multi-layered copper clusters and faceted nanoparticles were formed at higher copper loadings. • The active copper-ceria interface was constructed by the positively-charged copper atoms with the oxygen vacancies on ceria. • The WGS activity increased linearly with copper loading up to 15 mol.%. Cu species in the forms of layers, clusters and particles were dispersed on a rod-shaped ceria by a deposition-precipitation method and the resulting Cu/CeO 2 catalysts were tested for the low-temperature water-gas shift reaction. The structural, chemical and surface properties of the Cu/CeO 2 catalysts were analyzed by spectroscopic and microscopic techniques. It was identified that dispersion of copper on the rod-shaped ceria strongly depended on the metal loading (1–28 mol%): lower contents resulted in copper monolayers and/or bilayers while higher loadings led to multi-layered clusters and faceted particles. The copper-ceria interface was constructed by an intimate bonding of positively-charged copper atoms with oxygen vacancies on ceria, in a form of Cu+-O v -Ce3+, involving the electronic and geometric interactions between the copper atoms in the metal species and the oxygen vacancies on ceria. The overall activity increased linearly with the copper content in the range of 1–15 mol%, contributed mainly by copper monolayers and/or bilayers. Further increasing Cu loading up to 28 mol% only slightly enhanced the activity because of the presence of multilayered and crystalline Cu particles. This finding demonstrates that the dispersion of copper on the rod-shaped ceria depends on the loading of copper in the Cu/CeO 2 catalysts, which is associated with the number and density of the active sites. [ABSTRACT FROM AUTHOR]

Published
2020
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3. Water–gas shift catalysts based on ionic liquid mediated supported Cu nanoparticles

Author

Knapp, Richard, Wyrzgol, Sonja A., Jentys, Andreas, and Lercher, Johannes A.

Subjects
*GAS-liquid interfaces, *IONIC liquids, *COPPER, *NANOPARTICLES, *ALUMINUM oxide, *THIN films, *LOW temperatures, *CATALYSIS
Abstract

Abstract: The sorptive and catalytic properties of alumina supported Cu nanoparticles coated with a thin film of 1-butyl-2,3-dimethyl-imidazolium trifluoromethane sulfonate (BDiMIm) for low-temperature water–gas shift have been explored. For uncoated catalysts, the rate per gram catalyst passed through a maximum with increasing concentration of oxygen on the Cu surface. For reduced catalysts, the presence of oxygen facilitates the dissociation of water, while in excess it decreases the reaction rates due to limiting the reactant concentration. Catalysts coated with ionic liquid showed a higher turn over frequency for the water–gas shift reaction at low temperatures compared to uncoated catalysts and to the best commercial systems, which is attributed to a higher concentration of water in the proximity of the active sites and to the facile decomposition of carboxyl intermediates by the interaction with the ionic liquid. In addition, the presence of the ionic liquid reduces the sorption strength of CO leading to a better balance of the reactants at the surface. [Copyright &y& Elsevier]

Published
2010
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4. Low-temperature water-gas shift on Pt/Ce0.5La0.5O2 - δ: Effect of support synthesis method

Author

Petallidou, Klito C., Boghosian, Soghomon, Efstathiou, Angelos M., and Efstathiou, Angelos M. [0000-0001-8393-8800]

Subjects
Sol-gel synthesis of ceria-lanthana, Water gas shift, Analytical chemistry, Coprecipitation synthesis, Reaction intermediate, SSITKA-MS, Formate decomposition, Catalysis, Water-gas shift reaction, Oxalate, Temperature programmed techniques, symbols.namesake, chemistry.chemical_compound, Lanthanum oxides, Coprecipitation, Urea co-precipitation synthesis of ceria-lanthana, Sol-gels, Urea, Sol-gel process, Surface acidity and basicities, Platinum, Lanthana, Chemistry, Chemical shift, Temperature, Ceria-lanthana supported Pt, General Chemistry, Decomposition, SSITKA-DRIFTS, Kinetics, Lakes, Metabolism, Carbon dioxide, Synthesis (chemical), symbols, Catalyst activity, Titration, Reaction intermediates, Raman spectroscopy, Experiments, Low-temperature water-gas shift, Solid solution, Water-gas-shift reactions
Abstract

A series of 0.5 wt% Pt/Ce 0.5 La 0.5 O 2 − δ (Ce:La = 1:1) catalysts, the supports of which were prepared by different methods, namely: (i) sol–gel using citrate or oxalate as complexing agent, (ii) pechini, and (iii) urea co-precipitation, were investigated for the first time towards the water–gas shift (WGS) reaction in the 250–350 °C range and 1 atm total pressure. Towards a better understanding of the effect of support synthesis method on the intrinsic kinetic rate of WGS expressed per gram of catalyst (μmol CO g −1 s −1 ) or per length of the perimeter of Pt-support interface (μmol CO cm −1 s −1 ), a suite of various characterisation methods such as: in situ Raman, temperature-programmed techniques (TPD-H 2 , TPD-NH 3 , TPD-CO 2 ), powder XRD, and oxygen storage capacity (OSC) measurements were applied. The intrinsic kinetic rate of WGS (μmol CO g −1 s −1 ) was correlated with the concentration of the active “carbon-containing” (C-pool) and “hydrogen-containing” (H-pool) reaction intermediates formed within a reactive zone (Δ x , A) around each Pt nanoparticle (1.2–1.5 nm), parameters that were estimated via SSITKA and non steady-state transient isotopic and titration with water operando experiments. The urea co-precipitation method (U) resulted in the formation of a Ce 1 − x La x O 2 − δ solid solution with different composition (Ce:La atom ratio) than that formed by the other synthesis methods, which may be the main reason for Pt/Ce 0.5 La 0.5 O 2 − δ (U) to exhibit the highest by far CO conversion and kinetic rate towards the WGS compared to the other supported Pt catalysts. The same method (U) resulted in the formation of La 2 O 3 as opposed to the other methods. However, this was not considered as the main reason for explaining the higher activity of Pt supported on Ce 0.5 La 0.5 O 2 − δ (U) compared to the other carriers. The Ce 0.5 La 0.5 O 2 − δ (U) was also found to possess the highest surface acidity and basicity compared to the other supports but lower OSC (μmol g −1 ) (by more than 30% in the 250–550 °C range) than Ce 0.5 La 0.5 O 2 − δ prepared by the citrate sol–gel method, in harmony with the lower content of O vacancies in Ce 0.5 La 0.5 O 2 − δ (U) as evidenced by Raman studies. Transient DRIFTS formate (HCOO–) decomposition kinetic experiments towards CO 2 and H 2 formation have illustrated the importance of the presence of Pt and support composition.

Published
2015

5. Low-temperature water-gas shift on Pt/Ce1-xLaxO2-δ: Effect of Ce/La ratio

Author

Petallidou, Klito C., Efstathiou, Angelos M., and Efstathiou, Angelos M. [0000-0001-8393-8800]

Subjects
Reaction rates, Water gas shift, Water-gas shift reaction, Analytical chemistry, chemistry.chemical_element, Activation energy, Oxygen, Catalysis, symbols.namesake, OSC, Isotopes, 18O transient isotopic exchange, UV-vis/DRS, Reactivity (chemistry), Sol-gel process, Isotopic exchange, Chemical composition, Ce1-xLaxO2, General Environmental Science, Platinum, Apparent activation energy, Process Chemistry and Technology, Doping, Water-gas shift reaction (WGS), chemistry, Temperature-programmed surface reactions, symbols, Catalyst activity, Raman spectroscopy, Low-temperature water-gas shift, Surface reactions, Water-gas-shift reactions
Abstract

Pt nanoparticles (1.0-1.4nm size) supported on Ce1-xLaxO2-δ (x=0.0, 0.2, 05, 0.8 and 1.0) carriers, the latter prepared by the citrate sol-gel method, were tested toward the water-gas shift (WGS) reaction in the 200-400°C range. A deep insight into the effect of Ce/La atom ratio of support chemical composition on the catalytic performance (CO conversion vs. temperature and stability) and kinetic rates of Pt-loaded catalysts was realized after employing HAADF/STEM, in situ Raman and DRIFT spectroscopies under different gas atmospheres, temperature-programmed surface reaction (TPSR) in He and O2/He gas atmospheres following WGS reaction, CO-TPD, in situ UV-vis/DRS, oxygen storage capacity measurements, and transient 18O-isotopic exchange studies followed by WGS reaction. It was found that doping of ceria with 20at.% La3+ has increased significantly the catalytic activity of 0.5wt% Pt/Ce0.8La0.2O2-δ solid in the 250-350°C range, whereas addition of 50-80at.% La3+ in ceria caused a negative effect on the CO conversion with respect to pure ceria. It was found that the Ce/La atom ratio in Ce1-xLaxO2-δ influences the catalytic site reactivity (k) along the Pt-support interface. The optimum La3+-dopant concentration of 20at.% (Ce/La=4/1) used in Pt/Ce0.8La0.2O2 compared to the worst one of 80at.% (Pt/Ce0.2La0.8O2-δ, Ce/La=1/4) correlates with (i) the higher specific kinetic rate per length of Pt-support interface (μmol COcm-1s-1), (ii) the higher concentration of oxygen vacant sites, (iii) the lower amount (μmol/g-1) of "carbon" accumulated during WGS and best stability with time on stream, (iv) the lower apparent activation energy (kcalmol-1) of WGS reaction, (v) the lower degree toward Pt oxidation (largest Pt2+/Pt4+ ratio), (vi) the lower Ce1-xLaxO2-δ support energy band gap, and (vii) the lower mobility of surface lattice oxygen. © 2013 Elsevier B.V. 140-141 333 347 Cited By :39

Published
2013

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