Palladium catalysts are supported on TiO2, ZrO2, A12O3, Zro.sAlo.501.75 and TiO2-Zro.sAlo.501.75 prepared by co-precipitation method, re- spectively. Catalytic activities for methane and CO oxidation are evaluated in ...Palladium catalysts are supported on TiO2, ZrO2, A12O3, Zro.sAlo.501.75 and TiO2-Zro.sAlo.501.75 prepared by co-precipitation method, re- spectively. Catalytic activities for methane and CO oxidation are evaluated in a gas mixture that simulated the exhaust from lean-burn natural gas vehicles （NGVs）. Pd/TiO2-Zro.sAlo.501.75 performs the best catalytic activity among the tested five catalysts. For CH4, the light-off temperature （Tso） is 254 ℃, and the complete conversion temperature （Tgo） is 280 ℃; for CO, Tso is 84 ℃, and Tgo was 96 ℃. Various techniques, including N2 adsorption-desorption, X-ray diffraction （XRD）, H2-temperature-programmed reduction （H2-TPR）, X-ray photoelec- tron spectroscopy （XPS）, and scanning electron microscopy （SEM） are employed to characterize the effect of supports on the physicochemical properties of prepared catalysts. N2 adsorption-desorption and SEM show that TiO2-Zro.5Al0.501.75 expresses uniform nano-particles and large meso-pore diameters of 26 nm. H2-TPR and XRD indicate that PdO is well dispersed on the supports and strongly interacted with each other. The results of XPS show that the electron density around PdO and the proportion of active oxygen on TiO2-Zro.sAl0.501.75 are maxima among the five supports.展开更多
Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method...Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method）,CO-chemisorption and X-ray photoelectron spectroscopy （XPS）.The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles.The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor.It was found that the effect of Co significantly depended on the preparation process.PdCo/La-Al2O3 catalyst prepared by co-impregnation exhibited better water-resistant performance.The results of XPS indicated that both CoAl2O4 and Co3O4 were present in the Pd catalysts modified by Co.For the catalyst prepared by sequential impregnation method,the ratio of CoAl2O4/Co3O4 was higher than that of the catalyst prepared by co-impregnation method.It could be concluded that Co3O4 played an important role in improving water-resistant performance.展开更多
Herein,we report the excellent De-NO_(x)performance of La0.7Sr0.3MnO3(LSM)perovskite-supported Pd catalysts(Pd-LSM)in alternating lean-burn/fuel-rich atmospheres using C3H6 as reductant and describe the in situ activa...Herein,we report the excellent De-NO_(x)performance of La0.7Sr0.3MnO3(LSM)perovskite-supported Pd catalysts(Pd-LSM)in alternating lean-burn/fuel-rich atmospheres using C3H6 as reductant and describe the in situ activation of the Pd catalysts via metal-support interaction(MSI)tuning.The NO_(x)reduction conversion of the Pd-LSM catalyst increased significantly from 56.1%to 90.1%and the production of N2O was suppressed.Our results demonstrated that this behavior was mainly attributed to the in situ transformation of Pd2+into Pd0 during the reaction.The generated Pd0 species could readily activate the C3H6 reductant and achieve an eight-fold higher turnover frequency than Pd2+for the reduction of NO_(x).Moreover,excessive MSIs inhibited the in situ generation of Pd0,and thereby,lowered the De-NO_(x)activity of the catalyst even at high Pd dispersion.In addition,the Pd-LSM catalysts exhibited much higher S tolerance than conventional Al_(2)O_(3)-supported catalysts.Our study provides a new approach for analyzing and designing highly active metal catalysts operated under dynamic alternating oxidizing/reducing atmospheric conditions.展开更多
Herein,we report the high De-NOx performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn^(4+)...Herein,we report the high De-NOx performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn^(4+)/Mn^(3+) ratio and serious lattice contraction due to cationic nonstoichiometry.It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO_(3) phase.Our results demonstrate that below 300℃ the A-site defective perovskite can be more efficiently regenerated than the SrCO_(3) phase as NOx storage sites due to the latter’s stronger basicity,and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts.Both factors promote the lowtemperature De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst through improving its NOx trapping efficiency.Nevertheless,above 300℃,the NOx reduction becomes the determinant of the De-NOx activity of the perovskite-based catalysts.A-site defects can weaken the interactions between perovskite and Pd,inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative leanburn/fuel-rich atmospheric alternations,which boosts the De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The Pd/L_(0.5)Sr_(0.3)MnO_(3) catalyst exhibits the high sulfur tolerance as well.These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation,and have potential to be applied for various related catalyst systems.展开更多
Providing stable combustion of lean-burn natural gas engines was always a bigchallenge, particularly during a low load operation. In transient sea conditions, there is an additional concern due to irregular time-vary...Providing stable combustion of lean-burn natural gas engines was always a bigchallenge, particularly during a low load operation. In transient sea conditions, there is an additional concern due to irregular time-varying loads. Therefore, this study aimed at investigatingthe part-load operation of a marine spark-ignition lean-burn natural gas engine by simulatingthe entire engine. The engine’s essential components are modeled, including air manifold,intake valves, fuel system, controllers, combustion chamber, exhaust valves, exhaust manifoldand turbocharger.In steady-state, the results of emission compounds from modeling have been compared tomeasured data from 25% to 100% loads. For transient conditions, for the sample time of about50 min, the fuel flow and turbocharger output are selected from the vessel logged data andcompared with the simulation results. The model has shown the great potential of predictingthe engine response throughout the steady-state and transient conditions. Simulating the engineat part-load transient condition showed that the unburned hydrocarbon formation, known asmethane slip in lean-burn gas engines, is more than the part-load steady-state. This increaseof methane slip is due to the combustion instability in lower loads and flame extinguishingin such transient conditions. The engine measured data shows a double amount of methane slipin a 25% load than the 100% load in steady-state. However, the simulation output in the transient conditions confirms an increase in methane slip over four times than equivalentsteady-state load. Moreover, the lean-burn gas engine releases less NOX in part-load operationin a steady-state due to lower in-cylinder temperature. In transient conditions, there is remarkable instability in excess air ratio. Due to this instability, there is a rich mixture in instantaneoustime steps during loads up. Therefore, it will result in an unusually high amount of NOX, andmore than two times in comparison with the equivalent steady-state output.展开更多
A highly effective Ag-A_(2)O_(3) catalyst was pre-pared using the in-situ sol-gel method,and characterized by surface area using nitrogen adsorption,scanning electron microscopy(SEM),and transmission electron microsco...A highly effective Ag-A_(2)O_(3) catalyst was pre-pared using the in-situ sol-gel method,and characterized by surface area using nitrogen adsorption,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)techniques.The catalyst performance was tested on a real lean-burn gasoline engine.Only unburned hydrocarbons and carbon monoxide in the exhaust were directly used as reductant(without any external reductant),the maximum NO_(x) conversion could only reach 40% at 450°C.When an external reductant,ethanol was added,the average NO_(x) con-version was greater than 60%.At exhaust gas temperature range of 350-500°C,the maximum NO_(x) conversion reached about 90%.CO and HC could be efficiently oxidized with Pt-_(2)O_(3) oxidation catalyst placed at the end of SCR converter.However,NOx conversion drastically decreased because of the oxidation of some intermediates to NOx again.The possible reaction mechanism was proposed as two typical processes,nitration,and reduction in HC-SCR over Ag-Al_(2)O_(3).展开更多
The catalytic removal of NOx under lean condi- tions is one of the most important targets in catalysis re- search. The activities of metal oxides, zeolite-based catalysts and noble metal catalysts together with the fa...The catalytic removal of NOx under lean condi- tions is one of the most important targets in catalysis re- search. The activities of metal oxides, zeolite-based catalysts and noble metal catalysts together with the factors are influ- encing the selective reduction of NOx with hydrocarbons are reviewed. The reaction mechanisms for the three types of catalysts are briefly discussed. Recent progress in combined catalyst and NOx storage reduction catalysts is also intro- duced. Finally, future research directions are forecasted.展开更多
基金supported by the National Natural Science Foundation of China(21173153)
文摘Palladium catalysts are supported on TiO2, ZrO2, A12O3, Zro.sAlo.501.75 and TiO2-Zro.sAlo.501.75 prepared by co-precipitation method, re- spectively. Catalytic activities for methane and CO oxidation are evaluated in a gas mixture that simulated the exhaust from lean-burn natural gas vehicles （NGVs）. Pd/TiO2-Zro.sAlo.501.75 performs the best catalytic activity among the tested five catalysts. For CH4, the light-off temperature （Tso） is 254 ℃, and the complete conversion temperature （Tgo） is 280 ℃; for CO, Tso is 84 ℃, and Tgo was 96 ℃. Various techniques, including N2 adsorption-desorption, X-ray diffraction （XRD）, H2-temperature-programmed reduction （H2-TPR）, X-ray photoelec- tron spectroscopy （XPS）, and scanning electron microscopy （SEM） are employed to characterize the effect of supports on the physicochemical properties of prepared catalysts. N2 adsorption-desorption and SEM show that TiO2-Zro.5Al0.501.75 expresses uniform nano-particles and large meso-pore diameters of 26 nm. H2-TPR and XRD indicate that PdO is well dispersed on the supports and strongly interacted with each other. The results of XPS show that the electron density around PdO and the proportion of active oxygen on TiO2-Zro.sAl0.501.75 are maxima among the five supports.
基金supported by the National Natural Science Foundation of China (20773090)the Ph.D.Programs Foundation of Ministry of Education of China (200806100009)
文摘Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method）,CO-chemisorption and X-ray photoelectron spectroscopy （XPS）.The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles.The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor.It was found that the effect of Co significantly depended on the preparation process.PdCo/La-Al2O3 catalyst prepared by co-impregnation exhibited better water-resistant performance.The results of XPS indicated that both CoAl2O4 and Co3O4 were present in the Pd catalysts modified by Co.For the catalyst prepared by sequential impregnation method,the ratio of CoAl2O4/Co3O4 was higher than that of the catalyst prepared by co-impregnation method.It could be concluded that Co3O4 played an important role in improving water-resistant performance.
文摘Herein,we report the excellent De-NO_(x)performance of La0.7Sr0.3MnO3(LSM)perovskite-supported Pd catalysts(Pd-LSM)in alternating lean-burn/fuel-rich atmospheres using C3H6 as reductant and describe the in situ activation of the Pd catalysts via metal-support interaction(MSI)tuning.The NO_(x)reduction conversion of the Pd-LSM catalyst increased significantly from 56.1%to 90.1%and the production of N2O was suppressed.Our results demonstrated that this behavior was mainly attributed to the in situ transformation of Pd2+into Pd0 during the reaction.The generated Pd0 species could readily activate the C3H6 reductant and achieve an eight-fold higher turnover frequency than Pd2+for the reduction of NO_(x).Moreover,excessive MSIs inhibited the in situ generation of Pd0,and thereby,lowered the De-NO_(x)activity of the catalyst even at high Pd dispersion.In addition,the Pd-LSM catalysts exhibited much higher S tolerance than conventional Al_(2)O_(3)-supported catalysts.Our study provides a new approach for analyzing and designing highly active metal catalysts operated under dynamic alternating oxidizing/reducing atmospheric conditions.
基金the National Natural Science Foundation of China(21878213)。
文摘Herein,we report the high De-NOx performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn^(4+)/Mn^(3+) ratio and serious lattice contraction due to cationic nonstoichiometry.It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO_(3) phase.Our results demonstrate that below 300℃ the A-site defective perovskite can be more efficiently regenerated than the SrCO_(3) phase as NOx storage sites due to the latter’s stronger basicity,and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts.Both factors promote the lowtemperature De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst through improving its NOx trapping efficiency.Nevertheless,above 300℃,the NOx reduction becomes the determinant of the De-NOx activity of the perovskite-based catalysts.A-site defects can weaken the interactions between perovskite and Pd,inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative leanburn/fuel-rich atmospheric alternations,which boosts the De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The Pd/L_(0.5)Sr_(0.3)MnO_(3) catalyst exhibits the high sulfur tolerance as well.These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation,and have potential to be applied for various related catalyst systems.
文摘Providing stable combustion of lean-burn natural gas engines was always a bigchallenge, particularly during a low load operation. In transient sea conditions, there is an additional concern due to irregular time-varying loads. Therefore, this study aimed at investigatingthe part-load operation of a marine spark-ignition lean-burn natural gas engine by simulatingthe entire engine. The engine’s essential components are modeled, including air manifold,intake valves, fuel system, controllers, combustion chamber, exhaust valves, exhaust manifoldand turbocharger.In steady-state, the results of emission compounds from modeling have been compared tomeasured data from 25% to 100% loads. For transient conditions, for the sample time of about50 min, the fuel flow and turbocharger output are selected from the vessel logged data andcompared with the simulation results. The model has shown the great potential of predictingthe engine response throughout the steady-state and transient conditions. Simulating the engineat part-load transient condition showed that the unburned hydrocarbon formation, known asmethane slip in lean-burn gas engines, is more than the part-load steady-state. This increaseof methane slip is due to the combustion instability in lower loads and flame extinguishingin such transient conditions. The engine measured data shows a double amount of methane slipin a 25% load than the 100% load in steady-state. However, the simulation output in the transient conditions confirms an increase in methane slip over four times than equivalentsteady-state load. Moreover, the lean-burn gas engine releases less NOX in part-load operationin a steady-state due to lower in-cylinder temperature. In transient conditions, there is remarkable instability in excess air ratio. Due to this instability, there is a rich mixture in instantaneoustime steps during loads up. Therefore, it will result in an unusually high amount of NOX, andmore than two times in comparison with the equivalent steady-state output.
基金This work was financially supported by the National Natural Science foundation of China(Grant Nos.20507012 and 20437010)the National High-Tech Research and Development(863)Program of China(Grant No.2003AA642030)。
文摘A highly effective Ag-A_(2)O_(3) catalyst was pre-pared using the in-situ sol-gel method,and characterized by surface area using nitrogen adsorption,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)techniques.The catalyst performance was tested on a real lean-burn gasoline engine.Only unburned hydrocarbons and carbon monoxide in the exhaust were directly used as reductant(without any external reductant),the maximum NO_(x) conversion could only reach 40% at 450°C.When an external reductant,ethanol was added,the average NO_(x) con-version was greater than 60%.At exhaust gas temperature range of 350-500°C,the maximum NO_(x) conversion reached about 90%.CO and HC could be efficiently oxidized with Pt-_(2)O_(3) oxidation catalyst placed at the end of SCR converter.However,NOx conversion drastically decreased because of the oxidation of some intermediates to NOx again.The possible reaction mechanism was proposed as two typical processes,nitration,and reduction in HC-SCR over Ag-Al_(2)O_(3).
文摘The catalytic removal of NOx under lean condi- tions is one of the most important targets in catalysis re- search. The activities of metal oxides, zeolite-based catalysts and noble metal catalysts together with the factors are influ- encing the selective reduction of NOx with hydrocarbons are reviewed. The reaction mechanisms for the three types of catalysts are briefly discussed. Recent progress in combined catalyst and NOx storage reduction catalysts is also intro- duced. Finally, future research directions are forecasted.
