The Experts below are selected from a list of 77301 Experts worldwide ranked by ideXlab platform
Burtron H. Davis - One of the best experts on this subject based on the ideXlab platform.
-
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.
-
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.
-
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 .
-
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.
Gary Jacobs - One of the best experts on this subject based on the ideXlab platform.
-
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.
-
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.
-
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 .
-
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.
Robbie Burch - One of the best experts on this subject based on the ideXlab platform.
-
A critical analysis of the experimental evidence for and against a Formate mechanism for high activity water-gas shift catalysts
Applied Catalysis A: General, 2011Co-Authors: Robbie Burch, Alexandre Goguet, Frédéric C. MeunierAbstract:An in-depth analysis of the evidence for and against a Formate-based mechanism for the water-gas shift reaction has shown that with very few exceptions the published results cannot be used to provide any mechanistic information either for or against a Formate model. Where reliable quantitative data are available, these show unequivocally that for all high activity catalysts the contribution of IR-observable Formate to the production of CO2is only of minor importance. It is found that the Formates seen by IR typically account for less than about 10-15% of the total WGS reaction products. The Formates observed by IR were potentially the main reaction intermediates only in the case of very low activity catalysts. For the high activity catalysts that are of interest for current fuel cell applications it is clear that the major contribution of a Formate mechanism is yet to be proven. The current published in situ/operando FTIR data relating to Formates cannot be used to elucidate the main reaction mechanism nor for deriving improved catalytic formulations. © 2011 Elsevier B.V. All rights reserved.
-
quantitative analysis of the reactivity of Formate species seen by drifts over a au ce la o2 water gas shift catalyst first unambiguous evidence of the minority role of Formates as reaction intermediates
Journal of Catalysis, 2007Co-Authors: Frederic Meunier, Robbie Burch, Alexandre Goguet, D Reid, Weiling Deng, Sergiy O Shekhtman, Christopher Hardacre, Maria FlytzanistephanopoulosAbstract:The reactivity of the species formed at the surface of a Au/Ce(La)O2 catalyst during the water–gas shift (WGS) reaction were investigated by operando diffuse reflectance Fourier transform spectroscopy (DRIFTS) at the chemical steady state during isotopic transient kinetic analyses (SSITKA). The exchanges of the reaction product CO2 and of Formate and carbonate surface species were followed during an isotopic exchange of the reactant CO using a DRIFTS cell as a single reactor. The DRIFTS cell was a modified commercial cell that yielded identical reaction rates to that measured over a quartz plug-flow reactor. The DRIFTS signal was used to quantify the relative concentrations of the surface species and CO2. The analysis of the Formate exchange curves between 428 and 493 K showed that at least two levels of reactivity were present. “Slow Formates” displayed an exchange rate constant 10- to 20-fold slower than that of the reaction product CO2. “Fast Formates” were exchanged on a time scale similar to that of CO2. Multiple nonreactive readsorption of CO2 took place, accounting for the kinetics of the exchange of CO2(g) and making it impossible to determine the number of active sites through the SSITKA technique. The concentration (in mol g −1 )o f Formates on the catalyst was determined through a calibration curve and allowed calculation of the specific rate of Formate decomposition. The rate of CO2 formation was more than an order of magnitude higher than the rate of decomposition of Formates (slow + fast species), indicating that all of the Formates detected by DRIFTS could not be the main reaction intermediates in the production of CO2. This work stresses the importance of full quantitative analyses (measuring both rate constants and adsorbate concentrations) when investigating the role of adsorbates as potential reaction intermediates, and illustrates how even reactive species seen by DRIFTS may be unimportant in the overall reaction scheme.
Uschi M Graham - One of the best experts on this subject based on the ideXlab platform.
-
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 .
-
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.
Alexandre Goguet - One of the best experts on this subject based on the ideXlab platform.
-
A critical analysis of the experimental evidence for and against a Formate mechanism for high activity water-gas shift catalysts
Applied Catalysis A: General, 2011Co-Authors: Robbie Burch, Alexandre Goguet, Frédéric C. MeunierAbstract:An in-depth analysis of the evidence for and against a Formate-based mechanism for the water-gas shift reaction has shown that with very few exceptions the published results cannot be used to provide any mechanistic information either for or against a Formate model. Where reliable quantitative data are available, these show unequivocally that for all high activity catalysts the contribution of IR-observable Formate to the production of CO2is only of minor importance. It is found that the Formates seen by IR typically account for less than about 10-15% of the total WGS reaction products. The Formates observed by IR were potentially the main reaction intermediates only in the case of very low activity catalysts. For the high activity catalysts that are of interest for current fuel cell applications it is clear that the major contribution of a Formate mechanism is yet to be proven. The current published in situ/operando FTIR data relating to Formates cannot be used to elucidate the main reaction mechanism nor for deriving improved catalytic formulations. © 2011 Elsevier B.V. All rights reserved.
-
quantitative analysis of the reactivity of Formate species seen by drifts over a au ce la o2 water gas shift catalyst first unambiguous evidence of the minority role of Formates as reaction intermediates
Journal of Catalysis, 2007Co-Authors: Frederic Meunier, Robbie Burch, Alexandre Goguet, D Reid, Weiling Deng, Sergiy O Shekhtman, Christopher Hardacre, Maria FlytzanistephanopoulosAbstract:The reactivity of the species formed at the surface of a Au/Ce(La)O2 catalyst during the water–gas shift (WGS) reaction were investigated by operando diffuse reflectance Fourier transform spectroscopy (DRIFTS) at the chemical steady state during isotopic transient kinetic analyses (SSITKA). The exchanges of the reaction product CO2 and of Formate and carbonate surface species were followed during an isotopic exchange of the reactant CO using a DRIFTS cell as a single reactor. The DRIFTS cell was a modified commercial cell that yielded identical reaction rates to that measured over a quartz plug-flow reactor. The DRIFTS signal was used to quantify the relative concentrations of the surface species and CO2. The analysis of the Formate exchange curves between 428 and 493 K showed that at least two levels of reactivity were present. “Slow Formates” displayed an exchange rate constant 10- to 20-fold slower than that of the reaction product CO2. “Fast Formates” were exchanged on a time scale similar to that of CO2. Multiple nonreactive readsorption of CO2 took place, accounting for the kinetics of the exchange of CO2(g) and making it impossible to determine the number of active sites through the SSITKA technique. The concentration (in mol g −1 )o f Formates on the catalyst was determined through a calibration curve and allowed calculation of the specific rate of Formate decomposition. The rate of CO2 formation was more than an order of magnitude higher than the rate of decomposition of Formates (slow + fast species), indicating that all of the Formates detected by DRIFTS could not be the main reaction intermediates in the production of CO2. This work stresses the importance of full quantitative analyses (measuring both rate constants and adsorbate concentrations) when investigating the role of adsorbates as potential reaction intermediates, and illustrates how even reactive species seen by DRIFTS may be unimportant in the overall reaction scheme.