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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: Doping Ceria Improves Reducibility and Mobility of O-Bound Species and Catalyst Activity
Catalysis Letters, 2011Co-Authors: Linda Z. Linganiso, Gary Jacobs, Burtron H Davis, Venkat Ramana Rao Pendyala, Donald C. Cronauer, A. Jeremy Kropf, Christopher L. MarshallAbstract:A series of platinum loaded catalysts supported on cation (Me)-doped cerium dioxide (Me = Ba, La, Y, Hf and Zn) was prepared by co-precipitation of the Me-nitrates and impregnation of a Pt precursor. Low temperature water–gas shift activity depends on the nature of dopant employed, varying in the order of Ba > Y > Hf > La > undoped ceria > Zn. TPR-XANES measurements with flowing hydrogen reveal that adding dopants to ceria facilitate ceria reduction and increases the extents of both surface shell and bulk reduction of ceria. Experimental results confirm past theoretical models that dopants enhance both O-mobility and reducibility of ceria. DRIFTS measurements of the transient decomposition of Formates in steam suggest that formate half-life follows the trend Zn > undoped ceria > La > Hf > Y > Ba, indicating that the formate decomposition rate is enhanced by the addition of most of the dopants tested. Taken together, the results suggest that dopant addition improves the WGS rate by increasing the O-mobility of O-bound associated intermediates. Therefore, less Pt and Ce, which are expensive, is required to achieve comparable levels of activity. Graphical Abstract TPR-XANES profiles of 0.5% Pt/ceria catalyst with and without Y-dopant.
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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.
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reverse water gas shift reaction steady state isotope switching study of the reverse water gas shift reaction using in situ drifts and a pt ceria catalyst
Applied Catalysis A-general, 2005Co-Authors: Gary Jacobs, Burtron H DavisAbstract:Abstract A previous investigation using steady state isotope switching in combination with DRIFTS demonstrated that surface Formates exchange rapidly in a low temperature shift feed for the forward reaction. Transient decomposition of the pseudo-stable formate indicated that water autocatalyzes the forward shift reaction. In the present study, and including water in the RWGS feed (H 2 and CO 2 ), surface Formates were found to exchange more rapidly during RWGS over Pt/ceria than when a dry feed was used. An earlier claim suggested that Pt CO and carbonate were intermediates, as they exchange rapidly during RWGS. However, in the present study of 12 CO 2 to 13 CO 2 switching, Pt CO and carbonate exchange rapidly even in the absence of reaction . Furthermore, the formate exchange rate during RWGS in the absence of added water proceeds at a much slower rate, indicating that conclusions on the mechanism of forward shift cannot be inferred on the basis of dry RWGS results.
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low temperature water gas shift kinetic isotope effect observed for decomposition of surface Formates for pt ceria catalysts
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Uschi M Graham, Patricia M Patterson, Dennis E Sparks, Burtron H DavisAbstract:Abstract In previous work, steady-state isotope switching was conducted on Pt/ceria with H 2 O and D 2 O, and a normal kinetic isotope effect was observed. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that the surface coverage of H-formate was more limited by the WGS rate than that of D-formate, linking the rate limiting step to the breaking of the formate C–H bond. In this work, the transient response of the decomposition of H and D Formates was followed thermally and in the presence of H 2 O and D 2 O. A normal kinetic isotope effect was again obtained, in agreement with our previous findings, and those reported by Shido and Iwasawa. Consistent with their work, water was found to assist in promoting the forward decomposition of surface Formates to hydrogen and unidentate carbonate, the precursor to CO 2 .
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water gas shift in situ spectroscopic studies of noble metal promoted ceria catalysts for co removal in fuel cell reformers and mechanistic implications
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Leann Williams, Patricia M Patterson, Dennis E Sparks, Gerald A Thomas, Emilie Chenu, Burtron H DavisAbstract:Abstract In situ, steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements for adsorption of CO and for water-gas shift (WGS) reaction conditions indicate that Formates are present on the surface of reduced ceria, being formed by reaction with geminal OH groups that are present after reduction of the ceria surface shell. The process of surface shell reduction was strongly catalyzed by the presence of metal, while changing very little if at all the catalysis of bulk reduction. Gold was found to reduce the surface ceria at a lower temperature than that of platinum, but platinum gave a slightly higher degree of surface shell reduction. Under steady-state WGS at a high H 2 O/CO ratio, the concentrations of surface Formates are strongly limited at high CO conversions, while metalCO was not. Since under these conditions, CO exhibits a first order rate dependency, the active site should move to sparser coverages of CO, indicating that a formate mechanism is more likely the correct one. At low temperatures and conversions, the Formates were close to the equilibrium adsorption/desorption coverages obtained from only CO adsorption. In situ X-ray absorption near edge spectroscopy (XANES) directly links the metal to its ability to aid in catalyzing reduction of the surface shell of ceria. After surface shell reduction of ceria by hydrogen, addition of water to the hydrogen stream gave no indication of reoxidation whatsoever, as would be necessary under a ceria-mediated redox process. The reoxidation of ceria by water under helium alone was very slow, and only slight changes were recorded at 350 °C. Therefore, the results strongly favor a formate mechanistic scheme for low temperature water-gas shift. To date, most researchers have claimed a ceria-mediated redox process operating to describe the mechanism. Both mechanisms require reduction of the ceria surface.
Gary Jacobs - One of the best experts on this subject based on the ideXlab platform.
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Low-Temperature Water–Gas Shift: Doping Ceria Improves Reducibility and Mobility of O-Bound Species and Catalyst Activity
Catalysis Letters, 2011Co-Authors: Linda Z. Linganiso, Gary Jacobs, Burtron H Davis, Venkat Ramana Rao Pendyala, Donald C. Cronauer, A. Jeremy Kropf, Christopher L. MarshallAbstract:A series of platinum loaded catalysts supported on cation (Me)-doped cerium dioxide (Me = Ba, La, Y, Hf and Zn) was prepared by co-precipitation of the Me-nitrates and impregnation of a Pt precursor. Low temperature water–gas shift activity depends on the nature of dopant employed, varying in the order of Ba > Y > Hf > La > undoped ceria > Zn. TPR-XANES measurements with flowing hydrogen reveal that adding dopants to ceria facilitate ceria reduction and increases the extents of both surface shell and bulk reduction of ceria. Experimental results confirm past theoretical models that dopants enhance both O-mobility and reducibility of ceria. DRIFTS measurements of the transient decomposition of Formates in steam suggest that formate half-life follows the trend Zn > undoped ceria > La > Hf > Y > Ba, indicating that the formate decomposition rate is enhanced by the addition of most of the dopants tested. Taken together, the results suggest that dopant addition improves the WGS rate by increasing the O-mobility of O-bound associated intermediates. Therefore, less Pt and Ce, which are expensive, is required to achieve comparable levels of activity. Graphical Abstract TPR-XANES profiles of 0.5% Pt/ceria catalyst with and without Y-dopant.
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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.
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reverse water gas shift reaction steady state isotope switching study of the reverse water gas shift reaction using in situ drifts and a pt ceria catalyst
Applied Catalysis A-general, 2005Co-Authors: Gary Jacobs, Burtron H DavisAbstract:Abstract A previous investigation using steady state isotope switching in combination with DRIFTS demonstrated that surface Formates exchange rapidly in a low temperature shift feed for the forward reaction. Transient decomposition of the pseudo-stable formate indicated that water autocatalyzes the forward shift reaction. In the present study, and including water in the RWGS feed (H 2 and CO 2 ), surface Formates were found to exchange more rapidly during RWGS over Pt/ceria than when a dry feed was used. An earlier claim suggested that Pt CO and carbonate were intermediates, as they exchange rapidly during RWGS. However, in the present study of 12 CO 2 to 13 CO 2 switching, Pt CO and carbonate exchange rapidly even in the absence of reaction . Furthermore, the formate exchange rate during RWGS in the absence of added water proceeds at a much slower rate, indicating that conclusions on the mechanism of forward shift cannot be inferred on the basis of dry RWGS results.
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low temperature water gas shift kinetic isotope effect observed for decomposition of surface Formates for pt ceria catalysts
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Uschi M Graham, Patricia M Patterson, Dennis E Sparks, Burtron H DavisAbstract:Abstract In previous work, steady-state isotope switching was conducted on Pt/ceria with H 2 O and D 2 O, and a normal kinetic isotope effect was observed. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that the surface coverage of H-formate was more limited by the WGS rate than that of D-formate, linking the rate limiting step to the breaking of the formate C–H bond. In this work, the transient response of the decomposition of H and D Formates was followed thermally and in the presence of H 2 O and D 2 O. A normal kinetic isotope effect was again obtained, in agreement with our previous findings, and those reported by Shido and Iwasawa. Consistent with their work, water was found to assist in promoting the forward decomposition of surface Formates to hydrogen and unidentate carbonate, the precursor to CO 2 .
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water gas shift in situ spectroscopic studies of noble metal promoted ceria catalysts for co removal in fuel cell reformers and mechanistic implications
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Leann Williams, Patricia M Patterson, Dennis E Sparks, Gerald A Thomas, Emilie Chenu, Burtron H DavisAbstract:Abstract In situ, steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements for adsorption of CO and for water-gas shift (WGS) reaction conditions indicate that Formates are present on the surface of reduced ceria, being formed by reaction with geminal OH groups that are present after reduction of the ceria surface shell. The process of surface shell reduction was strongly catalyzed by the presence of metal, while changing very little if at all the catalysis of bulk reduction. Gold was found to reduce the surface ceria at a lower temperature than that of platinum, but platinum gave a slightly higher degree of surface shell reduction. Under steady-state WGS at a high H 2 O/CO ratio, the concentrations of surface Formates are strongly limited at high CO conversions, while metalCO was not. Since under these conditions, CO exhibits a first order rate dependency, the active site should move to sparser coverages of CO, indicating that a formate mechanism is more likely the correct one. At low temperatures and conversions, the Formates were close to the equilibrium adsorption/desorption coverages obtained from only CO adsorption. In situ X-ray absorption near edge spectroscopy (XANES) directly links the metal to its ability to aid in catalyzing reduction of the surface shell of ceria. After surface shell reduction of ceria by hydrogen, addition of water to the hydrogen stream gave no indication of reoxidation whatsoever, as would be necessary under a ceria-mediated redox process. The reoxidation of ceria by water under helium alone was very slow, and only slight changes were recorded at 350 °C. Therefore, the results strongly favor a formate mechanistic scheme for low temperature water-gas shift. To date, most researchers have claimed a ceria-mediated redox process operating to describe the mechanism. Both mechanisms require reduction of the ceria surface.
Dennis E Sparks - One of the best experts on this subject based on the ideXlab platform.
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low temperature water gas shift kinetic isotope effect observed for decomposition of surface Formates for pt ceria catalysts
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Uschi M Graham, Patricia M Patterson, Dennis E Sparks, Burtron H DavisAbstract:Abstract In previous work, steady-state isotope switching was conducted on Pt/ceria with H 2 O and D 2 O, and a normal kinetic isotope effect was observed. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that the surface coverage of H-formate was more limited by the WGS rate than that of D-formate, linking the rate limiting step to the breaking of the formate C–H bond. In this work, the transient response of the decomposition of H and D Formates was followed thermally and in the presence of H 2 O and D 2 O. A normal kinetic isotope effect was again obtained, in agreement with our previous findings, and those reported by Shido and Iwasawa. Consistent with their work, water was found to assist in promoting the forward decomposition of surface Formates to hydrogen and unidentate carbonate, the precursor to CO 2 .
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water gas shift in situ spectroscopic studies of noble metal promoted ceria catalysts for co removal in fuel cell reformers and mechanistic implications
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Leann Williams, Patricia M Patterson, Dennis E Sparks, Gerald A Thomas, Emilie Chenu, Burtron H DavisAbstract:Abstract In situ, steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements for adsorption of CO and for water-gas shift (WGS) reaction conditions indicate that Formates are present on the surface of reduced ceria, being formed by reaction with geminal OH groups that are present after reduction of the ceria surface shell. The process of surface shell reduction was strongly catalyzed by the presence of metal, while changing very little if at all the catalysis of bulk reduction. Gold was found to reduce the surface ceria at a lower temperature than that of platinum, but platinum gave a slightly higher degree of surface shell reduction. Under steady-state WGS at a high H 2 O/CO ratio, the concentrations of surface Formates are strongly limited at high CO conversions, while metalCO was not. Since under these conditions, CO exhibits a first order rate dependency, the active site should move to sparser coverages of CO, indicating that a formate mechanism is more likely the correct one. At low temperatures and conversions, the Formates were close to the equilibrium adsorption/desorption coverages obtained from only CO adsorption. In situ X-ray absorption near edge spectroscopy (XANES) directly links the metal to its ability to aid in catalyzing reduction of the surface shell of ceria. After surface shell reduction of ceria by hydrogen, addition of water to the hydrogen stream gave no indication of reoxidation whatsoever, as would be necessary under a ceria-mediated redox process. The reoxidation of ceria by water under helium alone was very slow, and only slight changes were recorded at 350 °C. Therefore, the results strongly favor a formate mechanistic scheme for low temperature water-gas shift. To date, most researchers have claimed a ceria-mediated redox process operating to describe the mechanism. Both mechanisms require reduction of the ceria surface.
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low temperature water gas shift in situ drifts reaction study of ceria surface area on the evolution of Formates on pt ceo2 fuel processing catalysts for fuel cell applications
Applied Catalysis A-general, 2003Co-Authors: Gary Jacobs, Leann Williams, Uschi M Graham, Dennis E Sparks, Gerald A Thomas, Burtron H DavisAbstract:Abstract Steady state infrared (IR) measurements for adsorption of only CO and under water–gas shift (WGS) reaction conditions indicate that Formates are present on the surface of reduced ceria, and that their concentrations vary with surface area of partially reduced ceria. Under steady state WGS, the concentrations of surface Formates are strongly limited at high CO conversions. However, at low temperatures and conversions, the Formates are close to the equilibrium adsorption/desorption coverages obtained from only CO adsorption. Comparisons at constant temperature indicate that formate bands from IR may provide an indication of the number of active sites present on the catalyst surface, as the rates varied accordingly. The IR results favor a formate intermediate mechanism to explain WGS. However, more kinetic studies are required, and over a broad range of temperatures, to verify this conclusion. Previous low temperature kinetic studies at a relatively high CO/H2O ratios have produced a zero-order dependency for CO and the authors related this to a mechanistic scheme involving reaction of Pt-CO with CeO2 to yield CO2, followed by reoxidation of Ce2O3 by H2O, with liberation of H2. The zero-order was suggested to be due to saturation of noble metal surface with CO during WGS. Saturation of ceria with carbonates was also reported. In this study, a high H2O/CO ratio was used where the CO rate dependency was first-order. This criteria requires that the surface coverage of the adsorbed CO intermediate should be reaction rate limited. Therefore, the Formates are suggested to be the intermediates.
Soon Hyeok Hong - One of the best experts on this subject based on the ideXlab platform.
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transfer hydrogenation of organic Formates and cyclic carbonates an alternative route to methanol from carbon dioxide
ACS Catalysis, 2014Co-Authors: Soon Hyeok HongAbstract:Transfer hydrogenation of organic Formates and cyclic carbonates was achieved for the first time using a readily available ruthenium catalyst. Nontoxic and economical 2-propanol was used, both as a solvent and hydrogen source, without the need of using flammable H2 gas under high pressure. This method provides an indirect strategy to produce methanol from carbon dioxide under mild conditions as well as an operationally simple and environmentally benign way to reduce Formates and carbonates.
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Transfer hydrogenation of organic Formates and cyclic carbonates: An alternative route to methanol from carbon dioxide
ACS Catalysis, 2014Co-Authors: Seung-hyo Kim, Soon Hyeok HongAbstract:Transfer hydrogenation of organic Formates and cyclic carbonates was achieved for the first time using a readily available ruthenium catalyst. Nontoxic and economical 2-propanol was used, both as a solvent and hydrogen source, without the need of using flammable H2 gas under high pressure. This method provides an indirect strategy to produce methanol from carbon dioxide under mild conditions as well as an operationally simple and environmentally benign way to reduce Formates and carbonates.\nTransfer hydrogenation of organic Formates and cyclic carbonates was achieved for the first time using a readily available ruthenium catalyst. Nontoxic and economical 2-propanol was used, both as a solvent and hydrogen source, without the need of using flammable H2 gas under high pressure. This method provides an indirect strategy to produce methanol from carbon dioxide under mild conditions as well as an operationally simple and environmentally benign way to reduce Formates and carbonates.
Leann Williams - One of the best experts on this subject based on the ideXlab platform.
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water gas shift in situ spectroscopic studies of noble metal promoted ceria catalysts for co removal in fuel cell reformers and mechanistic implications
Applied Catalysis A-general, 2004Co-Authors: Gary Jacobs, Leann Williams, Patricia M Patterson, Dennis E Sparks, Gerald A Thomas, Emilie Chenu, Burtron H DavisAbstract:Abstract In situ, steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements for adsorption of CO and for water-gas shift (WGS) reaction conditions indicate that Formates are present on the surface of reduced ceria, being formed by reaction with geminal OH groups that are present after reduction of the ceria surface shell. The process of surface shell reduction was strongly catalyzed by the presence of metal, while changing very little if at all the catalysis of bulk reduction. Gold was found to reduce the surface ceria at a lower temperature than that of platinum, but platinum gave a slightly higher degree of surface shell reduction. Under steady-state WGS at a high H 2 O/CO ratio, the concentrations of surface Formates are strongly limited at high CO conversions, while metalCO was not. Since under these conditions, CO exhibits a first order rate dependency, the active site should move to sparser coverages of CO, indicating that a formate mechanism is more likely the correct one. At low temperatures and conversions, the Formates were close to the equilibrium adsorption/desorption coverages obtained from only CO adsorption. In situ X-ray absorption near edge spectroscopy (XANES) directly links the metal to its ability to aid in catalyzing reduction of the surface shell of ceria. After surface shell reduction of ceria by hydrogen, addition of water to the hydrogen stream gave no indication of reoxidation whatsoever, as would be necessary under a ceria-mediated redox process. The reoxidation of ceria by water under helium alone was very slow, and only slight changes were recorded at 350 °C. Therefore, the results strongly favor a formate mechanistic scheme for low temperature water-gas shift. To date, most researchers have claimed a ceria-mediated redox process operating to describe the mechanism. Both mechanisms require reduction of the ceria surface.
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low temperature water gas shift in situ drifts reaction study of ceria surface area on the evolution of Formates on pt ceo2 fuel processing catalysts for fuel cell applications
Applied Catalysis A-general, 2003Co-Authors: Gary Jacobs, Leann Williams, Uschi M Graham, Dennis E Sparks, Gerald A Thomas, Burtron H DavisAbstract:Abstract Steady state infrared (IR) measurements for adsorption of only CO and under water–gas shift (WGS) reaction conditions indicate that Formates are present on the surface of reduced ceria, and that their concentrations vary with surface area of partially reduced ceria. Under steady state WGS, the concentrations of surface Formates are strongly limited at high CO conversions. However, at low temperatures and conversions, the Formates are close to the equilibrium adsorption/desorption coverages obtained from only CO adsorption. Comparisons at constant temperature indicate that formate bands from IR may provide an indication of the number of active sites present on the catalyst surface, as the rates varied accordingly. The IR results favor a formate intermediate mechanism to explain WGS. However, more kinetic studies are required, and over a broad range of temperatures, to verify this conclusion. Previous low temperature kinetic studies at a relatively high CO/H2O ratios have produced a zero-order dependency for CO and the authors related this to a mechanistic scheme involving reaction of Pt-CO with CeO2 to yield CO2, followed by reoxidation of Ce2O3 by H2O, with liberation of H2. The zero-order was suggested to be due to saturation of noble metal surface with CO during WGS. Saturation of ceria with carbonates was also reported. In this study, a high H2O/CO ratio was used where the CO rate dependency was first-order. This criteria requires that the surface coverage of the adsorbed CO intermediate should be reaction rate limited. Therefore, the Formates are suggested to be the intermediates.
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low temperature water gas shift in situ drifts reaction study of a pt ceo2 catalyst for fuel cell reformer applications
Journal of Physical Chemistry B, 2003Co-Authors: Gary Jacobs, Leann Williams, Uschi M Graham, And Dennis Sparks, Burtron H DavisAbstract:Steady-state IR measurements for adsorption of only CO and under WGS reaction indicate that Formates are present on the surface of partially reduced ceria, in contrast to a recent study, and that they are strongly limited at high CO conversions. At low temperatures and conversions, the Formates are close to the equilibrium adsorption/desorption coverages obtained from CO adsorption alone. The Formates are close to saturation at low temperatures. These IR results favor the bidentate formate mechanism in explaining WGS. However, more kinetic studies are required and over a wider range of temperatures. While low-temperature kinetic studies have found a zero-order dependency for CO and related this to saturation of a noble metal surface, this study indicates that one cannot rule out the possibility of the formate mechanism on this basis, as CO is also close to saturation as an adsorbed formate at the low temperatures used in previous studies.
