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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 strategy to lower pt loading by doping Ceria with ca2 improves formate mobility wgs rate by increasing Surface o mobility
Applied Catalysis A-general, 2011Co-Authors: Linda Z Linganiso, Uschi M. Graham, Burtron H. Davis, Gary Jacobs, Khalid G Azzam, Donald C Cronauer, Jeremy A Kropf, Christopher L MarshallAbstract:In one view, the metal–oxide synergy (e.g., Pt metal and cerium oxide) has been explained in terms of the dehydrogenation of formate formed on the Surface of the partially reducible oxide (PRO) by Pt across the interface, with H2O participating in the transition state of forward formate decomposition. In this work, Ca-doping of the Ceria component in Pt/Ceria catalysts was demonstrated by TPR and TPR–XANES measurements to facilitate the temperature of Ceria Surface shell and bulk reduction steps, and by TPR–XANES to increase the extents of Surface shell and bulk reduction of Ceria. The results thus confirm, experimentally, past theoretical models, which suggested that divalent elements (e.g., Ca) enhance both O-mobility and reducibility of Ceria by weakening the Ce–O bond through lattice strain. This strain was also detected in our XRD measurements. A recent Surface diffusion model postulated that increasing oxygen Surface diffusion also improves the mobility of O-bound intermediates (e.g., formates, carbonates, carboxylates). In this work, in situ DRIFTS measurements confirm that improved formate decomposition rates were realized over the Ca-doped Pt promoted Ceria catalysts possessing higher O-mobility relative to undoped Pt/Ceria. In turn, improved LT-WGS rates were observed over the Ca-doped Pt/Ceria catalysts. While the precise mechanism is still under debate, the enhanced mobility of O-bound intermediates by Ca-doping is suggested to be responsible for the significant boosts in CO conversion levels and TOFs observed during LT-WGS. Thus, doping Ceria with elements like Ca provides a path forward for lowering the precious metal content (e.g., Pt), as well as the rare earth content (e.g., Ce) – catalytic components that are becoming increasingly expensive.
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LOW TEMPERATURE WATER GAS SHIFT: IMPACT OF PT PROMOTER LOADING ON THE PARTIAL REDUCTION OF Ceria AND CONSEQUENCES FOR CATALYST DESIGN
Journal of Catalysis, 2005Co-Authors: Gary Jacobs, Patricia M Patterson, Emilie Chenu, Uschi M. Graham, Alan Dozier, Burtron H. DavisAbstract:Abstract Partial reduction of Ceria generates catalytically active bridging OH groups on the Surface of Ceria. Pt facilitates this Surface reduction process, and in this work, the impact of the Pt promoter loading on catalyst structural-property relationships was explored. XANES spectra were recorded under H2 treatment for a series of Pt/Ceria catalysts with increasing Pt loading at both the Pt and Ce L III edges. Reduction of Pt oxide was hindered by metal–support interactions, such that higher Pt loadings facilitated reduction of Pt oxide to Pt0. Two routes of bridging OH group formation are as follows: (1) once it is reduced, Pt0 dissociates H2, which spills over to the Ceria Surface to generate the bridging OH group active sites directly, accompanied by a change in the oxidation state of the Ce atoms involved with the sites from Ce4+ to Ce3+; and (2) H2 or CO removes Ceria Surface capping oxygen atoms to generate vacancies (and Surface Ce3+), followed by H2O dissociation at the vacancies to generate the bridging OH groups. Either route highlights the direct link between the extent of Ceria partial reduction and the active site density of the bridging OH group active sites. The relative Ce3+ and Ce4+ concentrations from XANES were quantified and at low temperature; the greatest degree of Ceria reduction was obtained for the Pt/Ceria catalysts with higher Pt loadings, correlating with a higher bridging OH group active site density. Using in situ DRIFTS, we used CO as a probe molecule, as it reacts with the bridging OH groups to generate Surface formates, the proposed intermediates of the WGS reaction. While addition of CO to the unpromoted catalyst reduced at 250 °C led to only very weak formate bands due to a lack of bridging OH groups on the Ceria Surface at that temperature, strong formate bands arose on the Surface of the Pt/Ceria catalysts at 250 °C. In situ DRIFTS was also utilized to probe the dynamics of the Surface formate coverages under low-temperature WGS reaction conditions over the Pt/Ceria series. A high H2O/CO feed ratio was employed, and the Surface formate coverages were found to be more limited by the WGS rate for the heavily loaded Pt/Ceria catalysts. This indicates that Pt may not only serve to facilitate the generation of the bridging OH group active sites at low temperature, but may also be involved in accelerating Surface formate decomposition, the elementary step of the mechanism that is proposed to be rate limiting. A clear trend of higher CO conversion with higher Pt loading was established in reaction testing. HR-TEM carried out on the 5%Pt/Ceria catalyst indicated well-dispersed Pt clusters in the diameter range of 1–2 nm.
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low temperature water gas shift role of pretreatment on formation of Surface carbonates and formates
Catalysis Letters, 2004Co-Authors: Gary Jacobs, Leann Williams, Patricia M Patterson, Dennis E Sparks, Burtron H. DavisAbstract:Recently, the role of Ceria vacancies on water–gas shift activity has been explained in terms of a redox mechanism, whereby CO adsorbed on a metal reduces the Ceria Surface to generate CO2, and water reoxidizes the Ceria Surface to CeO2, liberating hydrogen in the process. In this study, we examine the possibility of a Ceria-mediated redox mechanism by examining more closely the evolution of carbonate and formate bands under different controlled treatment environments, and utilizing different reduction procedures. Earlier it was claimed that the decomposition of carbonates by water was consistent with a redox process, whereby the CO2 product could spillover to the support. We found that the observation of carbonate formation and decomposition by water was a result of the treatment procedure used in the earlier work, and that, once bridging OH groups are produced in the presence of water, the reaction more likely proceeds via a formate intermediate, which is produced by reaction of CO with the active bridging OH groups. However, the vacancies appear to play an important role in generating these active sites. Possible pathways to active site generation are discussed.
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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, Dennis E Sparks, Gerald A Thomas, Uschi M. Graham, 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.
Pavel Janoš - One of the best experts on this subject based on the ideXlab platform.
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mesoporous cerium oxide for fast degradation of aryl organophosphate flame retardant triphenyl phosphate
RSC Advances, 2019Co-Authors: Jakub Ederer, Martin Sťastný, Marek Došek, Jiří Henych, Pavel JanošAbstract:Cerium oxide nanoparticles were prepared by calcination of basic cerous carbonate (as a precursor) obtained by precipitation from an aqueous solution. Prepared samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HRSEM), BET (Brunauer–Emmett–Teller) Surface area and porosity measurement. Prepared cerium oxide was applied as a destructive sorbent for the fast and safe degradation of organophosphorus flame retardant triphenyl phosphate (TPP). It was shown that cerium dioxide was effective in the decomposition of TPP by cleavage of the P–O–aryl bond in the flame retardant molecule. A degradation mechanism for TPP on the Ceria Surface was proposed. The degradation is governed by conversion of TPP via diphenyl phosphate (DPP) to the final product identified as phenol (Ph). The key parameter increasing the degradation efficiency of CeO2 is the temperature of calcination. At optimum calcination temperature (500 °C), the produced Ceria retains a sufficiently high Surface area and attains an optimum degree of crystallinity (related to a number of crystal defects, and thus potential reactive sites). The fast and efficient degradation of organophosphorus flame retardant TPP was observed in a polar aprotic solvent (acetonitrile) that is miscible with water.
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mesoporous cerium oxide for fast degradation of aryl organophosphate flame retardant triphenyl phosphate
RSC Advances, 2019Co-Authors: Jakub Ederer, Martin Sťastný, Marek Došek, Jiří Henych, Pavel JanošAbstract:Cerium oxide nanoparticles were prepared by calcination of basic cerous carbonate (as a precursor) obtained by precipitation from an aqueous solution. Prepared samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HRSEM), BET (Brunauer–Emmett–Teller) Surface area and porosity measurement. Prepared cerium oxide was applied as a destructive sorbent for the fast and safe degradation of organophosphorus flame retardant triphenyl phosphate (TPP). It was shown that cerium dioxide was effective in the decomposition of TPP by cleavage of the P–O–aryl bond in the flame retardant molecule. A degradation mechanism for TPP on the Ceria Surface was proposed. The degradation is governed by conversion of TPP via diphenyl phosphate (DPP) to the final product identified as phenol (Ph). The key parameter increasing the degradation efficiency of CeO2 is the temperature of calcination. At optimum calcination temperature (500 °C), the produced Ceria retains a sufficiently high Surface area and attains an optimum degree of crystallinity (related to a number of crystal defects, and thus potential reactive sites). The fast and efficient degradation of organophosphorus flame retardant TPP was observed in a polar aprotic solvent (acetonitrile) that is miscible with water.
Gary Jacobs - One of the best experts on this subject based on the ideXlab platform.
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low temperature water gas shift strategy to lower pt loading by doping Ceria with ca2 improves formate mobility wgs rate by increasing Surface o mobility
Applied Catalysis A-general, 2011Co-Authors: Linda Z Linganiso, Uschi M. Graham, Burtron H. Davis, Gary Jacobs, Khalid G Azzam, Donald C Cronauer, Jeremy A Kropf, Christopher L MarshallAbstract:In one view, the metal–oxide synergy (e.g., Pt metal and cerium oxide) has been explained in terms of the dehydrogenation of formate formed on the Surface of the partially reducible oxide (PRO) by Pt across the interface, with H2O participating in the transition state of forward formate decomposition. In this work, Ca-doping of the Ceria component in Pt/Ceria catalysts was demonstrated by TPR and TPR–XANES measurements to facilitate the temperature of Ceria Surface shell and bulk reduction steps, and by TPR–XANES to increase the extents of Surface shell and bulk reduction of Ceria. The results thus confirm, experimentally, past theoretical models, which suggested that divalent elements (e.g., Ca) enhance both O-mobility and reducibility of Ceria by weakening the Ce–O bond through lattice strain. This strain was also detected in our XRD measurements. A recent Surface diffusion model postulated that increasing oxygen Surface diffusion also improves the mobility of O-bound intermediates (e.g., formates, carbonates, carboxylates). In this work, in situ DRIFTS measurements confirm that improved formate decomposition rates were realized over the Ca-doped Pt promoted Ceria catalysts possessing higher O-mobility relative to undoped Pt/Ceria. In turn, improved LT-WGS rates were observed over the Ca-doped Pt/Ceria catalysts. While the precise mechanism is still under debate, the enhanced mobility of O-bound intermediates by Ca-doping is suggested to be responsible for the significant boosts in CO conversion levels and TOFs observed during LT-WGS. Thus, doping Ceria with elements like Ca provides a path forward for lowering the precious metal content (e.g., Pt), as well as the rare earth content (e.g., Ce) – catalytic components that are becoming increasingly expensive.
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LOW TEMPERATURE WATER GAS SHIFT: IMPACT OF PT PROMOTER LOADING ON THE PARTIAL REDUCTION OF Ceria AND CONSEQUENCES FOR CATALYST DESIGN
Journal of Catalysis, 2005Co-Authors: Gary Jacobs, Patricia M Patterson, Emilie Chenu, Uschi M. Graham, Alan Dozier, Burtron H. DavisAbstract:Abstract Partial reduction of Ceria generates catalytically active bridging OH groups on the Surface of Ceria. Pt facilitates this Surface reduction process, and in this work, the impact of the Pt promoter loading on catalyst structural-property relationships was explored. XANES spectra were recorded under H2 treatment for a series of Pt/Ceria catalysts with increasing Pt loading at both the Pt and Ce L III edges. Reduction of Pt oxide was hindered by metal–support interactions, such that higher Pt loadings facilitated reduction of Pt oxide to Pt0. Two routes of bridging OH group formation are as follows: (1) once it is reduced, Pt0 dissociates H2, which spills over to the Ceria Surface to generate the bridging OH group active sites directly, accompanied by a change in the oxidation state of the Ce atoms involved with the sites from Ce4+ to Ce3+; and (2) H2 or CO removes Ceria Surface capping oxygen atoms to generate vacancies (and Surface Ce3+), followed by H2O dissociation at the vacancies to generate the bridging OH groups. Either route highlights the direct link between the extent of Ceria partial reduction and the active site density of the bridging OH group active sites. The relative Ce3+ and Ce4+ concentrations from XANES were quantified and at low temperature; the greatest degree of Ceria reduction was obtained for the Pt/Ceria catalysts with higher Pt loadings, correlating with a higher bridging OH group active site density. Using in situ DRIFTS, we used CO as a probe molecule, as it reacts with the bridging OH groups to generate Surface formates, the proposed intermediates of the WGS reaction. While addition of CO to the unpromoted catalyst reduced at 250 °C led to only very weak formate bands due to a lack of bridging OH groups on the Ceria Surface at that temperature, strong formate bands arose on the Surface of the Pt/Ceria catalysts at 250 °C. In situ DRIFTS was also utilized to probe the dynamics of the Surface formate coverages under low-temperature WGS reaction conditions over the Pt/Ceria series. A high H2O/CO feed ratio was employed, and the Surface formate coverages were found to be more limited by the WGS rate for the heavily loaded Pt/Ceria catalysts. This indicates that Pt may not only serve to facilitate the generation of the bridging OH group active sites at low temperature, but may also be involved in accelerating Surface formate decomposition, the elementary step of the mechanism that is proposed to be rate limiting. A clear trend of higher CO conversion with higher Pt loading was established in reaction testing. HR-TEM carried out on the 5%Pt/Ceria catalyst indicated well-dispersed Pt clusters in the diameter range of 1–2 nm.
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low temperature water gas shift role of pretreatment on formation of Surface carbonates and formates
Catalysis Letters, 2004Co-Authors: Gary Jacobs, Leann Williams, Patricia M Patterson, Dennis E Sparks, Burtron H. DavisAbstract:Recently, the role of Ceria vacancies on water–gas shift activity has been explained in terms of a redox mechanism, whereby CO adsorbed on a metal reduces the Ceria Surface to generate CO2, and water reoxidizes the Ceria Surface to CeO2, liberating hydrogen in the process. In this study, we examine the possibility of a Ceria-mediated redox mechanism by examining more closely the evolution of carbonate and formate bands under different controlled treatment environments, and utilizing different reduction procedures. Earlier it was claimed that the decomposition of carbonates by water was consistent with a redox process, whereby the CO2 product could spillover to the support. We found that the observation of carbonate formation and decomposition by water was a result of the treatment procedure used in the earlier work, and that, once bridging OH groups are produced in the presence of water, the reaction more likely proceeds via a formate intermediate, which is produced by reaction of CO with the active bridging OH groups. However, the vacancies appear to play an important role in generating these active sites. Possible pathways to active site generation are discussed.
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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, Dennis E Sparks, Gerald A Thomas, Uschi M. Graham, 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.
Jakub Ederer - One of the best experts on this subject based on the ideXlab platform.
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mesoporous cerium oxide for fast degradation of aryl organophosphate flame retardant triphenyl phosphate
RSC Advances, 2019Co-Authors: Jakub Ederer, Martin Sťastný, Marek Došek, Jiří Henych, Pavel JanošAbstract:Cerium oxide nanoparticles were prepared by calcination of basic cerous carbonate (as a precursor) obtained by precipitation from an aqueous solution. Prepared samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HRSEM), BET (Brunauer–Emmett–Teller) Surface area and porosity measurement. Prepared cerium oxide was applied as a destructive sorbent for the fast and safe degradation of organophosphorus flame retardant triphenyl phosphate (TPP). It was shown that cerium dioxide was effective in the decomposition of TPP by cleavage of the P–O–aryl bond in the flame retardant molecule. A degradation mechanism for TPP on the Ceria Surface was proposed. The degradation is governed by conversion of TPP via diphenyl phosphate (DPP) to the final product identified as phenol (Ph). The key parameter increasing the degradation efficiency of CeO2 is the temperature of calcination. At optimum calcination temperature (500 °C), the produced Ceria retains a sufficiently high Surface area and attains an optimum degree of crystallinity (related to a number of crystal defects, and thus potential reactive sites). The fast and efficient degradation of organophosphorus flame retardant TPP was observed in a polar aprotic solvent (acetonitrile) that is miscible with water.
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mesoporous cerium oxide for fast degradation of aryl organophosphate flame retardant triphenyl phosphate
RSC Advances, 2019Co-Authors: Jakub Ederer, Martin Sťastný, Marek Došek, Jiří Henych, Pavel JanošAbstract:Cerium oxide nanoparticles were prepared by calcination of basic cerous carbonate (as a precursor) obtained by precipitation from an aqueous solution. Prepared samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HRSEM), BET (Brunauer–Emmett–Teller) Surface area and porosity measurement. Prepared cerium oxide was applied as a destructive sorbent for the fast and safe degradation of organophosphorus flame retardant triphenyl phosphate (TPP). It was shown that cerium dioxide was effective in the decomposition of TPP by cleavage of the P–O–aryl bond in the flame retardant molecule. A degradation mechanism for TPP on the Ceria Surface was proposed. The degradation is governed by conversion of TPP via diphenyl phosphate (DPP) to the final product identified as phenol (Ph). The key parameter increasing the degradation efficiency of CeO2 is the temperature of calcination. At optimum calcination temperature (500 °C), the produced Ceria retains a sufficiently high Surface area and attains an optimum degree of crystallinity (related to a number of crystal defects, and thus potential reactive sites). The fast and efficient degradation of organophosphorus flame retardant TPP was observed in a polar aprotic solvent (acetonitrile) that is miscible with water.
Suttichai Assabumrungrat - One of the best experts on this subject based on the ideXlab platform.
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catalytic steam reforming of ethane and propane over ceo2 doped ni al2o3 at sofc temperature improvement of resistance toward carbon formation by the redox property of doping ceo2
Fuel, 2006Co-Authors: Navadol Laosiripojana, W Sangtongkitcharoen, Suttichai AssabumrungratAbstract:Abstract Ni/Al 2 O 3 with the doping of CeO 2 was found to have useful activity to reform ethane and propane with steam under Solid Oxide Fuel Cells (SOFCs) conditions, 700–900 °C. CeO 2 -doped Ni/Al 2 O 3 with 14% Ceria doping content showed the best reforming activity among those with the Ceria content between 0 and 20%. The amount of carbon formation decreased with increasing Ce content. However, Ni was easily oxidized when more than 16% of Ceria was doped. Compared to conventional Ni/Al 2 O 3 , 14%CeO 2 -doped Ni/Al 2 O 3 provides significantly higher reforming reactivity and resistance toward carbon deposition. These enhancements are mainly due to the influence of the redox properties of doped Ceria. Regarding the temperature programmed reduction experiments (TPR-1), the redox properties and the oxygen storage capacity (OSC) for the catalysts increased with increasing Ce doping content. In addition, it was also proven in the present work that the redox of these catalysts are reversible, according to the temperature programmed oxidation (TPO) and the second time temperature programmed reduction (TPR-2) results. During the reforming process, in addition to the reactions on Ni Surface, the gas–solid reactions between the gaseous components presented in the system (C 2 H 6 , C 3 H 8 , C 2 H 4 , CH 4 , CO 2 , CO, H 2 O, and H 2 ) and the lattice oxygen (O x ) on Ceria Surface also take place. The reactions of adsorbed Surface hydrocarbons with the lattice oxygen (O x ) on Ceria Surface (C n H m +O x → n CO+ m /2(H 2 )+O x − n ) can prevent the formation of carbon species on Ni Surface from hydrocarbons decomposition reaction (C n H m ⇔ n C+ m /2H 2 ). Moreover, the formation of carbon via Boudard reaction (2CO⇔CO 2 +C) is also reduced by the gas–solid reaction of carbon monoxide (produced from steam reforming) with the lattice oxygen (CO+O x ⇔CO 2 +O x −1 ).
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synthesis gas production from dry reforming of methane over ceo2 doped ni al2o3 influence of the doping Ceria on the resistance toward carbon formation
Chemical Engineering Journal, 2005Co-Authors: Navadol Laosiripojana, W Sutthisripok, Suttichai AssabumrungratAbstract:Abstract Doping of CeO2 as an additive promoter on Ni/Al2O3 was found to improve dry reforming activity for H2 and CO productions at solid oxide fuel cell (SOFC) operating temperature (800–900 °C). The catalyst provides significantly higher reforming reactivity and resistance toward carbon deposition compared to conventional Ni/Al2O3. These enhancements are mainly due to the influence of the redox property of Ceria. During dry reforming process, in addition to the reactions on Ni Surface, the gas–solid reactions between the gaseous components presented in the system (CH4, CO2, CO, H2O, and H2) and the lattice oxygen (Ox) on Ceria Surface also take place. The reactions of adsorbed methane and carbon monoxide (produced during dry reforming process) with the lattice oxygen (Ox) on Ceria Surface (CH4 + Ox → CO + H2 + Ox−1 and CO + Ox ⇔ CO2 + Ox−1) can prevent the formation of carbon species on Ni Surface from methane decomposition reaction and Boudard reaction. In particular, CeO2 doped Ni/Al2O3 with 8% Ceria content showed the best reforming activity among those with the Ceria content between 0 and 14%. The amount of carbon formation decreased with increasing Ce content. However, Ni was oxidized when more than 10% of Ceria was doped. According to the post-XPS measurement, a small formation of Ce2O3 was observed after exposure in dry methane reforming conditions with low inlet CH4/CO2 ratio (1.0/0.3). The intrinsic reaction kinetics of 8% CeO2 doped Ni/Al2O3 was studied by varying inlet CH4 and CO2 concentrations, and by adding H2 and CO to the system at different temperatures. The dry reforming rate increased with increasing methane partial pressure and the operating temperature. The reaction orders in methane were always closed to 1.0 in all conditions. Carbon dioxide also presented weak positive impact on the methane conversion, whereas adding of carbon monoxide and hydrogen inhibited the reforming rate.
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catalytic dry reforming of methane over high Surface area Ceria
Applied Catalysis B-environmental, 2005Co-Authors: Navadol Laosiripojana, Suttichai AssabumrungratAbstract:Abstract High Surface area Ceria (CeO 2 (HSA)), synthesized by a surfactant-assisted approach, was found to have useful dry reforming activity for H 2 and CO production under solid oxide fuel cells (SOFCs) conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to Ni/Al 2 O 3 and conventional low Surface area Ceria (CeO 2 (LSA)) under dry reforming conditions. These enhancements are due to the high redox property of CeO 2 (HSA). During the dry reforming process, the redox reactions between the gaseous components in the system and the lattice oxygen (O x ) take place on Ceria Surface. Among these reactions, the rapid redox reactions of carbon compounds such as CH 4 , and CO with lattice oxygen (CH 4 + O x → CO + H 2 + O x −1 and CO + O x = CO 2 + O x −1 ) can prevent the formation of carbon species from the methane decomposition and Boudard reactions even at low inlet carbon dioxide concentration. In particular, the dry reforming rate over CeO 2 (HSA) is proportional to the methane partial pressure and the operating temperature. Carbon dioxide presents weak positive impact on the methane conversion, whereas both carbon monoxide and hydrogen inhibit the reforming rate. The activation energies and reforming rates under the same methane concentration for CeO 2 toward the dry reforming are almost equal to the steam reforming as previously reported [1–4] . This result suggests the similar reaction mechanisms for both the steam reforming and the dry reforming over CeO 2 ; i.e., the dry reforming rate is governed by the slow reaction of adsorbed methane, or Surface hydrocarbon species, with oxygen in CeO 2 , and a rapid gas–solid reaction between CO 2 and CeO 2 to replenish the oxygen.