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T Tabakova - One of the best experts on this subject based on the ideXlab platform.
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viability of au ceo2 zno al2o3 catalysts for pure hydrogen production by the Water Gas Shift reaction
Chemcatchem, 2014Co-Authors: Tomas Ramirez Reina, V Idakiev, T Tabakova, Svetlana Ivanova, M A Centeno, Juan Jose Delgado, Ivan Ivanov, J A OdriozolaAbstract:The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the Water–Gas Shift reaction. Herein, a series of gold catalysts supported on ZnO-promoted CeO2–Al2O3 are presented as interesting systems for the purification of H2 streams through the Water–Gas Shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn-containing solids. High activity and good stability and resistance towards start-up–shut-down situations was found, which makes these catalysts a promising alternative for CO clean-up applications.
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low temperature Water Gas Shift reaction over au ceo2 catalysts
Catalysis Today, 2002Co-Authors: D Andreeva, V Idakiev, T Tabakova, L Ilieva, Polycarpos Falaras, Athanasios B Bourlinos, A TravlosAbstract:A high and stable activity for gold/ceria catalyts has been established for the Water-Gas Shift reaction. The relationship between gold loading and catalytic activity was studied over a wide temperature range. The influence of space velocity and H2O/CO ratio at different temperatures on the catalytic activity and stability was also investigated. The reduction/oxidation processes of ceria in the presence of gold was readily followed by TPR measurements. It was shown that ceria plays the role of an active support capable of producing oxygen. The high and stable activity of gold/ceria catalysts could arise from the high and stable gold dispersion present during the catalytic operation.
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low temperature Water Gas Shift reaction on auα fe2o3 catalyst
Applied Catalysis A-general, 1996Co-Authors: D Andreeva, V Idakiev, T Tabakova, A Andreev, R GiovanoliAbstract:The Water-Gas Shift reaction (WGSR) has been studied on Auα-Fe2O3 catalyst. The structure of the samples has been investigated by chemical and physical methods—TEM, X-ray, DTA, FTIR. A high dispersion degree of the gold particles and an increased concentration of the hydroxyl groups on Auα-Fe2O3 has been established in comparison to the pure α-Fe2O3. The results obtained can be explained on the basis of the associative mechanism of the WGSR. The essential aspects are the dissociative adsorption of Water on ultrafine gold particles, followed by spillover of active hydroxyl groups onto adjacent sites of the ferric oxide. The formation and decomposition of intermediate species is accompanied by redox transfer Fe3+ Fe2+ in Fe3O4.
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low temperature Water Gas Shift reaction over au α fe2o3
Journal of Catalysis, 1996Co-Authors: D Andreeva, V Idakiev, T Tabakova, A AndreevAbstract:This paper gives a short account of results associated with the high catalytic activity of metallic gold, deposited on ferric oxide, in the Water-Gas Shift (WGS) reaction. Until now there have been no literature data on the catalytic activity of gold in that important industrial reaction except some results for the hydrogenation of CO{sub 2}. 8 refs., 1 fig.
V Idakiev - One of the best experts on this subject based on the ideXlab platform.
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viability of au ceo2 zno al2o3 catalysts for pure hydrogen production by the Water Gas Shift reaction
Chemcatchem, 2014Co-Authors: Tomas Ramirez Reina, V Idakiev, T Tabakova, Svetlana Ivanova, M A Centeno, Juan Jose Delgado, Ivan Ivanov, J A OdriozolaAbstract:The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the Water–Gas Shift reaction. Herein, a series of gold catalysts supported on ZnO-promoted CeO2–Al2O3 are presented as interesting systems for the purification of H2 streams through the Water–Gas Shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn-containing solids. High activity and good stability and resistance towards start-up–shut-down situations was found, which makes these catalysts a promising alternative for CO clean-up applications.
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low temperature Water Gas Shift reaction over au ceo2 catalysts
Catalysis Today, 2002Co-Authors: D Andreeva, V Idakiev, T Tabakova, L Ilieva, Polycarpos Falaras, Athanasios B Bourlinos, A TravlosAbstract:A high and stable activity for gold/ceria catalyts has been established for the Water-Gas Shift reaction. The relationship between gold loading and catalytic activity was studied over a wide temperature range. The influence of space velocity and H2O/CO ratio at different temperatures on the catalytic activity and stability was also investigated. The reduction/oxidation processes of ceria in the presence of gold was readily followed by TPR measurements. It was shown that ceria plays the role of an active support capable of producing oxygen. The high and stable activity of gold/ceria catalysts could arise from the high and stable gold dispersion present during the catalytic operation.
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low temperature Water Gas Shift reaction on auα fe2o3 catalyst
Applied Catalysis A-general, 1996Co-Authors: D Andreeva, V Idakiev, T Tabakova, A Andreev, R GiovanoliAbstract:The Water-Gas Shift reaction (WGSR) has been studied on Auα-Fe2O3 catalyst. The structure of the samples has been investigated by chemical and physical methods—TEM, X-ray, DTA, FTIR. A high dispersion degree of the gold particles and an increased concentration of the hydroxyl groups on Auα-Fe2O3 has been established in comparison to the pure α-Fe2O3. The results obtained can be explained on the basis of the associative mechanism of the WGSR. The essential aspects are the dissociative adsorption of Water on ultrafine gold particles, followed by spillover of active hydroxyl groups onto adjacent sites of the ferric oxide. The formation and decomposition of intermediate species is accompanied by redox transfer Fe3+ Fe2+ in Fe3O4.
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low temperature Water Gas Shift reaction over au α fe2o3
Journal of Catalysis, 1996Co-Authors: D Andreeva, V Idakiev, T Tabakova, A AndreevAbstract:This paper gives a short account of results associated with the high catalytic activity of metallic gold, deposited on ferric oxide, in the Water-Gas Shift (WGS) reaction. Until now there have been no literature data on the catalytic activity of gold in that important industrial reaction except some results for the hydrogenation of CO{sub 2}. 8 refs., 1 fig.
Robbie Burch - One of the best experts on this subject based on the ideXlab platform.
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deactivation mechanism of a au cezro4 catalyst during a low temperature Water Gas Shift reaction
Journal of Physical Chemistry C, 2007Co-Authors: Alexandre Goguet, Robbie Burch, Y Chen, Christopher Hardacre, P Hu, Richard W Joyner, Frederic Meunier, And D Thompsett, Daniele TibilettiAbstract:On-stream deactivation during a Water Gas Shift (WGS) reaction over gold supported on a ceria−zirconia catalyst was examined. Although the fresh catalyst has very high low temperature ( 250 °C. This process reduces the metal−support interaction, which is considered to be critical in determining the high activity of the catalyst.
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gold catalysts for pure hydrogen production in the Water Gas Shift reaction activity structure and reaction mechanism
Physical Chemistry Chemical Physics, 2006Co-Authors: Robbie BurchAbstract:The production of hydrogen containing very low levels of carbon monoxide for use in polymer electrolyte fuel cells requires the development of catalysts that show very high activity at low temperatures where the equilibrium for the removal of carbon monoxide using the Water–Gas Shift reaction is favourable. It has been claimed that oxide-supported gold catalysts have the required high activity but there is considerable uncertainty in the literature about the feasibility of using these catalysts under real conditions. By comparing the activity of gold catalysts with that of platinum catalysts it is shown that well-prepared gold catalysts are significantly more active than the corresponding platinum catalysts. However, the method of preparation and pre-treatment of the gold catalysts is critical and activity variations of several orders of magnitude can be observed depending on the methods chosen. It is shown that an intimate contact between gold and the oxide support is important and any preparative procedure that does not generate such an interaction, or any subsequent treatment that can destroy such an interaction, may result in catalysts with low activity. The oxidation state and structure of active gold catalysts for the Water–Gas Shift reaction is shown to comprise gold primarily in a zerovalent metallic state but in intimate contact with the support. This close contact between small metallic gold particles and the support may result in the “atoms” at the point of contact having a net charge (most probably cationic) but the high activity is associated with the presence of metallic gold. Both in situ XPS and XANES appear unequivocal on this point and this conclusion is consistent with similar measurements on gold catalysts even when used for CO oxidation. In situ EXAFS measurements under Water Gas Shift conditions show that the active form of gold is a small gold cluster in intimate contact with the oxide support. The importance of the gold/oxide interface is indicated but the possible role of special sites (e.g., edge sites) on the gold clusters cannot be excluded. These may be important for CO oxidation but the fact that Water has to be activated in the Water Gas Shift reaction may point towards a more dominant role for the interfacial sites. The mechanism of the Water Gas Shift reaction on gold and other low temperature catalysts has been widely investigated but little agreement exists. However, it is shown that a single “universal” model is consistent with much of the experimental literature. In this, it is proposed that the dominant surface intermediate is a function of reaction conditions. For example, as the temperature is increased the dominant species changes from a carbonate or carboxylate species, to a formate species and eventually at high temperatures to a mechanism that is characteristic of a redox process. Similar changes in the dominant intermediate are observed with changes in the Gas composition. Overall, it is shown that reported variations in the kinetics, structure and reaction mechanism for the Water Gas Shift reaction on gold catalysts can now be understood and rationalised.
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gold catalysts for pure hydrogen production in the Water Gas Shift reaction activity structure and reaction mechanism
Physical Chemistry Chemical Physics, 2006Co-Authors: Robbie BurchAbstract:The production of hydrogen containing very low levels of carbon monoxide for use in polymer electrolyte fuel cells requires the development of catalysts that show very high activity at low temperatures where the equilibrium for the removal of carbon monoxide using the Water–Gas Shift reaction is favourable. It has been claimed that oxide-supported gold catalysts have the required high activity but there is considerable uncertainty in the literature about the feasibility of using these catalysts under real conditions. By comparing the activity of gold catalysts with that of platinum catalysts it is shown that well-prepared gold catalysts are significantly more active than the corresponding platinum catalysts. However, the method of preparation and pre-treatment of the gold catalysts is critical and activity variations of several orders of magnitude can be observed depending on the methods chosen. It is shown that an intimate contact between gold and the oxide support is important and any preparative procedure that does not generate such an interaction, or any subsequent treatment that can destroy such an interaction, may result in catalysts with low activity. The oxidation state and structure of active gold catalysts for the Water–Gas Shift reaction is shown to comprise gold primarily in a zerovalent metallic state but in intimate contact with the support. This close contact between small metallic gold particles and the support may result in the “atoms” at the point of contact having a net charge (most probably cationic) but the high activity is associated with the presence of metallic gold. Both in situ XPS and XANES appear unequivocal on this point and this conclusion is consistent with similar measurements on gold catalysts even when used for CO oxidation. In situ EXAFS measurements under Water Gas Shift conditions show that the active form of gold is a small gold cluster in intimate contact with the oxide support. The importance of the gold/oxide interface is indicated but the possible role of special sites (e.g., edge sites) on the gold clusters cannot be excluded. These may be important for CO oxidation but the fact that Water has to be activated in the Water Gas Shift reaction may point towards a more dominant role for the interfacial sites. The mechanism of the Water Gas Shift reaction on gold and other low temperature catalysts has been widely investigated but little agreement exists. However, it is shown that a single “universal” model is consistent with much of the experimental literature. In this, it is proposed that the dominant surface intermediate is a function of reaction conditions. For example, as the temperature is increased the dominant species changes from a carbonate or carboxylate species, to a formate species and eventually at high temperatures to a mechanism that is characteristic of a redox process. Similar changes in the dominant intermediate are observed with changes in the Gas composition. Overall, it is shown that reported variations in the kinetics, structure and reaction mechanism for the Water Gas Shift reaction on gold catalysts can now be understood and rationalised.
Sung-hwan Han - One of the best experts on this subject based on the ideXlab platform.
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development of zno al2o3 catalyst for reverse Water Gas Shift reaction of camere carbon dioxide hydrogenation to form methanol via a reverse Water Gas Shift reaction process
Applied Catalysis A-general, 2001Co-Authors: Sang Woo Park, Oh Shim Joo, Kwang-deog Jung, Hyo Kim, Sung-hwan HanAbstract:Abstract ZnO and ZnO/Al2O3 catalysts were studied for a reverse-Water-Gas-Shift reaction (RWReaction). The catalytic activities depended on the compositions of Zn and Al at the temperature range of 673–973 K and GHSV of 15,000. The activities were close to the equilibrium conversion at temperatures above 873 K. The catalysts were characterized by using BET, TPR, XRD, SEM, and TEM. The ZnO/Al2O3 catalysts were mixtures of ZnO and ZnAl2O4 phases, and the particle size of the ZnO was strongly dependent on its composition in the ZnO/Al2O3 catalysts. ZnO/Al2O3 (Zn:Al=1:1) catalyst has the smallest particle size of ZnO and its conversion of CO2 at 873 K and GHSV of 150,000 was 43%. The stability of ZnO/Al2O3 catalysts increased in the presence of the large particles of ZnO. Hence, ZnO/Al2O3 (Zn:Al=4:1) catalyst was more stable than the ZnO/Al2O3 (Zn:Al=1:1) catalyst. The conversion of CO2 on the ZnO/Al2O3 (Zn:Al=1:1) catalyst decreased from 43 to 17% in 48 h. The ZnO in ZnO/Al2O3 catalysts was reduced to the Zn metal during the RWReaction, which contributed to the deactivation of the ZnO/Al2O3 catalysts. Meanwhile, the activity of ZnAl2O4 catalyst was stable for 100 h at 873 K and GHSV of 150,000. The ZnAl2O4 catalyst was developed for the RWReaction of the CAMERE (carbon dioxide hydrogenation to form methanol via a reverse-Water-Gas-Shift reaction) process for methanol formation from CO2.
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Carbon dioxide hydrogenation to form methanol via a reverse-Water-Gas- Shift reaction (the CAMERE process)
Industrial and Engineering Chemistry Research, 1999Co-Authors: Oh Shim Joo, Alexander Ya Rozovskii, Galina I. Lin, Sung-hwan Han, Kwang-deog Jung, Il Moon, Sung Jin UhmAbstract:The CAMERE process (carbon dioxide hydrogenation to form methanol via a reverse-Water-Gas-Shift reaction) was developed and evaluated. The reverse-Water-Gas-Shift reactor and the methanol synthesis reactor were serially aligned to form methanol from CO2 hydrogenation. Carbon dioxide was converted to CO and Water by the reverse-Water-Gas-Shift reaction (RWReaction) to remove Water before methanol was synthesized. With the elimination of Water by RWReaction, the purge Gas volume was minimized as the recycle Gas volume decreased. Because of the minimum purge Gas loss by the pretreatment of RWReactor, the overall methanol yield increased up to 89% from 69%. An active and stable catalyst with the composition of Cu/ ZnO/ZrO2/Ga2O3 (5:3:1:1) was developed. The system was optimized and compared with the commercial methanol synthesis processes from natural Gas and coal.
Burtron H. Davis - One of the best experts on this subject based on the ideXlab platform.
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low temperature Water Gas Shift alkali doping to facilitate formate c h bond cleaving over pt ceria catalysts an optimization problem
Catalysis Letters, 2008Co-Authors: Harold N Evin, Gary Jacobs, J Ruizmartinez, Gerald A Thomas, Burtron H. DavisAbstract:Doping Pt/ceria catalysts with alkali metals was found to lead to an important weakening of the formate C–H bond, as demonstrated by a Shift to lower wavenumbers of the ν(CH) vibrational mode. However, with high alkalinity (∼2.5%Na or equimolar amounts of K, Rb, or Cs), a tradeoff was observed such that while the formate became more reactive, the stability of the carbonate species, which arises from the formate decomposition, was found to increase. This was observed by TPD-MS measurements of the adsorbed CO2 probe molecule. Increasing the amount of alkali to levels that were too high also led to lower catalyst BET surface area, the blocking of the Pt surface sites as observed in infrared measurements, and also a Shift to higher temperature of the surface shell reduction step of ceria during TPR. When the alkalinity was too high, the CO conversion rate during Water–Gas Shift decreased in comparison with the undoped Pt/ceria catalyst. However, at lower levels of alkali, the abovementioned inhibiting factors on the Water–Gas Shift rate were alleviated such that the weakening of the formate C–H bond could be utilized to improve the overall turnover efficiency during the Water–Gas Shift cycle. This was demonstrated at 0.5%Na (or equimolar equivalent levels of K) doping levels. Not only was the formate turnover rate found to increase significantly during both transient and steady state DRIFTS tests, but this effect was accompanied by a notable increase in the CO conversion rate during low temperature Water–Gas Shift.
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low temperature Water Gas Shift the effect of alkali doping on the ch bond of formate over pt zro2 catalysts
Applied Catalysis A-general, 2007Co-Authors: J M Pigos, Gary Jacobs, Christopher J Brooks, Burtron H. DavisAbstract:Abstract Using combinatorial methods, doping Pt/ZrO 2 with alkali cations such as Li, especially Na, and K, was found to have a positive impact on the low temperature Water–Gas Shift rate. In this investigation, DRIFTS results indicate that the alkali cation significantly Shifts the formate C H band positions toward lower wavenumbers in the order K (2774 cm −1 ) −1 ) −1 ) −1 ). Not only were the bands Shifted, but the overall intensities were found to be higher with the addition of alkali promoter. Three separate tests were conducted to probe the stability of formates, including (1) steady state experiments at 225 °C; (2) transient formate decomposition studies at 130 °C in steam; and (3) dry hydrogen–deuterium exchange tests at 225 °C. In each case, the alkali significantly impacted the formate decomposition rate, due to the weakening of the formate C H bond. The results suggest a new direction in Water Gas Shift catalyst design.
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low temperature Water Gas Shift characterization and testing of binary mixed oxides of ceria and zirconia promoted with pt
Applied Catalysis A-general, 2006Co-Authors: Sandrine Ricote, Gary Jacobs, Mark Milling, Patricia M Patterson, Burtron H. DavisAbstract:Abstract A series of Pt promoted ceria–zirconia mixed oxides was prepared, characterized, and tested for the low temperature Water–Gas Shift reaction. An enhancement in the Water–Gas Shift rate was observed by doping zirconium atoms into ceria to form a binary oxide for Pt promoted catalysts. By characterization using TPR and XANES, doping zirconia to ceria decreased the temperature for the surface reduction step. However, the total number of bridging OH group defect sites decreased, as Zr remained to a great extent in the Zr 4+ oxidation state. This was confirmed by CO adsorption, whereby the density of total surface formates was found to decline with increased Zr concentrations. However, the formate forward turnover rate in steam was increased by zirconia addition, and was found to be higher than either Pt/ceria or Pt/zirconia alone. Both the overall rate of the formate decomposition and the Water–Gas Shift rate, as measured by the CO conversion, passed through a maximum with increasing Zr content. Two types of formates were observed, those associated with a ceria-rich surface phase, and those associated with a zirconia-rich surface phase. The relative amounts of the two formates correlated with the Zr/Ce atomic ratios obtained by XPS. EXAFS results provided direct evidence that a solid solution was present in the mixed oxide, as a distinct peak in the Fourier transform magnitude corresponding to the Zr–Ce interaction was observed, increasing with increasing Ce/Zr ratio. The sensitivity to added carbon dioxide in the feed of the undoped and a Zr doped catalyst was also explored.
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Water Gas Shift steady state isotope switching study of the Water Gas Shift reaction over pt ceria using in situ drifts
Catalysis Letters, 2005Co-Authors: Gary Jacobs, Adam C Crawford, Burtron H. DavisAbstract:The stability of surface formates generated by reaction of bridging OH groups with CO is an important first criterion supporting the idea that the rate limiting step of WGS involves formate decomposition. The second important factor is that, in the presence of Water, shown directly by the measurements obtained during this steady state isotope switching study, the forward decomposition of surface formates to CO2 and H2 is strongly auto-catalyzed by H2O, in agreement with the findings of Shido and Iwasawa. Based on a normal kinetic isotope effect previously observed with H2O:D2O switching and the response of surface formate coverages to the WGS rate under steady state conditions when a high H2O:CO ratio is employed, the conclusion is drawn that a surface formate mechanism is likely operating for the low temperature Water Gas Shift reaction.
