Designing metal compounds based on their structure and chemical composition is essential in achieving desirable performance in methane oxidation,because of the synergistic effect between different metal elements.Herei...Designing metal compounds based on their structure and chemical composition is essential in achieving desirable performance in methane oxidation,because of the synergistic effect between different metal elements.Herein,a bimetallic Ru-Pt catalyst on TiO_(2) support(RuPt-O/TiO_(2)) was prepared by in situ reduction followed by calcination in air.Compared with monometallic catalysts(Ru-O/TiO_(2) and Pt-O/TiO_(2)),the synergistic effect of mixed metals endowed bimetallic catalysts with excellent stability and outstanding performance in methane oxidation,with a reaction rate of 13.9×10^(-5)mol^(-1)_(CH_(4))·g^(-1)_(Ru+Pt)·s^(-1)at 303℃.The varied characterization results revealed that among the bimetallic catalysts,RuO_(2)was epitaxially grown on the TiO_(2) substrate owing to lattice matching between them,and part of the PtO_(x) adhered to the RuO_(2) surface,in addition to a single PtO_(x) nanoparticle with 4 nm in size.Consequently,Pt mainly existed in the form of Pt2+and Pt4+and a small amount of zero valence in the bimetallic catalyst,prompting the adsorption and activation of methane as the first and rate-controlling step for CH_(4) oxidation.More importantly,the RuO_(2) species provided additional oxygen species to facilitate the redox cycle of the PtO_(x) species.This study opens a new route for structurally designing promising catalysts for CH4oxidation.展开更多
A series of Cu-SSZ-13 catalysts with the same Cu loading were prepared by different methods of incipient wetness impregnation [Cu-SSZ-13(IWI)], ion exchange[Cu-SSZ-13(IE)] and hydro-thermal synthesis [Cu-SSZ-13(HTS)]....A series of Cu-SSZ-13 catalysts with the same Cu loading were prepared by different methods of incipient wetness impregnation [Cu-SSZ-13(IWI)], ion exchange[Cu-SSZ-13(IE)] and hydro-thermal synthesis [Cu-SSZ-13(HTS)]. Their activity for selective catalytic reduction of nitrogen oxides(NO_x) with NH3 was determined. The results show that the Cu-SSZ-13(HTS) catalyst exhibits a better ammonia selective catalytic reduction(NH3-SCR)activity compared with the other two catalysts, over which more than 90% NO conversion is obtained at 215-600℃under the space velocity of 180,000 h^(-1). The characterization results reveal that the Cu-SSZ-13(HTS) catalyst possesses more amount of stable Cu^(2+) in the six-membered ring and high ability for NH3 and NO adsorption, leading to its high NH3-SCR activity, although this catalyst has low surface area. On the other hand, the activity of Cu-SSZ-13(IE) catalyst is almost the same as that of Cu-SSZ-13(IWI) catalyst at the temperature lower than 400 ℃, but the activity of the former is much higher than that of the latter at > 400 ℃ due to the high activity of Cu-SSZ-13(IWI) catalyst for NH3 oxidation.展开更多
A series of 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2 catalysts were prepared by impregnation method based on the presynthesis of Sn_(0.9)Ce_(0.1)O_2 support prepared by co-precipitation method, and then characterized by Brunaue...A series of 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2 catalysts were prepared by impregnation method based on the presynthesis of Sn_(0.9)Ce_(0.1)O_2 support prepared by co-precipitation method, and then characterized by Brunauer–Emmett–Teller(BET), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Raman, CO chemical adsorption and hydrogen temperature-programmed reduction(H_2-TPR) techniques. The effect of calcination temperature of the composite oxide support on the catalytic performances of the Pd/Sn_(0.9)Ce_(0.1)O_2 catalyst for the CH_4 total oxidation was studied. It is found that the catalytic activity of the Pd/Sn_(0.9)Ce_(0.1)O_2 catalyst increases with the increase in calcination temperature of the Pd/Sn_(0.9)Ce_(0.1)O_2 support. The 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2/1100 catalyst(the Pd/Sn_(0.9)Ce_(0.1)O_2 support was calcined at 1100 ℃) exhibits the best reactive activity(T_(10)= 255 ℃). The excellent activity of the 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2/1100 catalyst should be attributed to the high reducibility of PdO, the excellent oxygen mobility of the support and the high content of active Pd^(2+) species on the Pd/Sn_(0.9)Ce_(0.1)O_2 catalyst.展开更多
The unsupported Cu and Ag catalysts with different oxidation states were prepared, and their catalytic performances for propylene epoxidation were investigated.The metallic Cu catalyst exhibits much higher catalytic a...The unsupported Cu and Ag catalysts with different oxidation states were prepared, and their catalytic performances for propylene epoxidation were investigated.The metallic Cu catalyst exhibits much higher catalytic activity and propylene oxide(PO) selectivity than Cu2 O and Cu O catalysts.The Cu0 species are the main active sites for propylene epoxidation, but Cu2 O and Cu O species are in favor of CO2 and acrolein production.The PO selectivity of 54.2 % and propylene conversion of 2.6 % can be achieved over the metallic Cu catalyst at 160 °C in initial stage, but metallic Cu catalyst would be oxidized to Cu2 O during propylene epoxidation, resulting in a sharp decrease in the PO selectivity and propylene conversion.Nanosize Ag Cuxbimetallic catalysts were prepared.It is found that adding Ag to the metallic Cu catalysts can prevent the oxidation of Cu and make Ag Cuxbimetallic catalysts more stable under the condition of propylene epoxidation.The Ag/Cu molar ratio can remarkably affect the catalytic performance of Ag Cuxcatalyst and the selectivity to PO and acrolein.After Ag Cuxwas supported on MOx-modified a-Al2O3, its catalytic performance can be improved and has a close relationship with the acid–base property of support.展开更多
Development of active and stable catalysts for low-temperature CO oxidation has long been regarded as a hot topic.In this contribution,we used CeO_(2) with high-density surface pits as support to prepare an active and...Development of active and stable catalysts for low-temperature CO oxidation has long been regarded as a hot topic.In this contribution,we used CeO_(2) with high-density surface pits as support to prepare an active and stable Au/CeO_(2) catalyst by an adsorption-deposition method.The obtained 0.05 wt%Au/CeO_(2)-TD(where TD represents thermal decomposition)can maintain its activity at 80℃ for more than 20 h or even after calcination at 800℃ for 2 h.The characterization results showed that the high-density surface pits on CeO_(2)-TD play a decisive role in the stabilization of Au and enhancement of the redox property.This work may provide a new strategy to improve the stability of supported metal catalysts by a simple and conventional method.展开更多
Au-Cu bimetallic nanoparticles with uniform size,shape,and compositions were synthesized by wet chemistry method,and then the Au-Cu/SiO_(2) catalyst supported on SiO_(2) was prepared.Meanwhile,their catalytic activity...Au-Cu bimetallic nanoparticles with uniform size,shape,and compositions were synthesized by wet chemistry method,and then the Au-Cu/SiO_(2) catalyst supported on SiO_(2) was prepared.Meanwhile,their catalytic activity for the selective oxidation of propene to acrolein using O_(2) as an oxidant was evaluated.The bimetallic catalyst shows a significantly enhanced catalytic performance comparing with Au and Cu monometallic catalysts.Characterization of the materials and kinetic study was conducted to explore the cooperating mechanism of Au and Cu for improving the catalytic activity of the bimetallic catalyst.Cu component can segregate to the alloy surface and the Au-Cu alloy transferred to Au-CuO core/shell structure after annealing during the preparation process.Based on the Mars-van Krevelen mechanism for the selective oxidation of propene over the prepared catalysts,the coexistence of CuO can promote the adsorption and activation of O_(2).Meanwhile,the electrons transfer from Au to Cu in the catalyst can facilitate the adsorptions of both oxygen on CuO sites and propene on Au sites.The combined effects of the above two aspects result in the high catalytic activity of the Au-Cu/SiO_(2) catalyst for selective oxidation of propene to acrolein,compared to the Au/SiO_(2) and CuO/SiO_(2) catalysts.展开更多
A series of Co_(3) O_(4) catalysts was prepared by ammonia(Co-AP) and oxalate(Co-OP) precipitation,solgel(Co-SG),and urea hydrothermal(Co-UH) methods,and their physicochemical properties were characterised by numerous...A series of Co_(3) O_(4) catalysts was prepared by ammonia(Co-AP) and oxalate(Co-OP) precipitation,solgel(Co-SG),and urea hydrothermal(Co-UH) methods,and their physicochemical properties were characterised by numerous techniques including X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nitrogen sorption,X-ray photoelectron spectroscopy(XPS),temperature-programmed reduction of H_(2)(H_(2)-TPR),temperature-programmed desorption of O_(2)(O_(2)-TPD),and temperature-programmed desorption of NH_(3)(NH_(3)-TPD).The catalytic activity of each catalyst was estimated for the catalytic combustion of vinyl chloride(VC) emissions.The crystallite size of the Co_(3) O_(4) catalyst was found to be well correlated with the amounts of surface-adsorbed oxygen species and number of acid sites on the catalyst surface,and consequently,determined several physicochemical properties of the catalyst.Of the catalysts studied here,the Co-AP catalyst exhibits the smallest crystallite size,which increases the specific surface area and the concentration of Co^(2+) on the catalyst surface.This,in turn,enhances the redox property,oxygen mobility,and the number of acid sites associated with the Co-AP catalyst.In fact,the Co-AP catalyst exhibits the best catalytic activity for VC combustion at 360℃and does not produce any chlorinated by-products.展开更多
Recent studies suggested that the interactions between particles can induce aggregative nucleation and growth processes beyond those predicted by the traditional LaMer model of nanoparticle formation,but their nucleat...Recent studies suggested that the interactions between particles can induce aggregative nucleation and growth processes beyond those predicted by the traditional LaMer model of nanoparticle formation,but their nucleation and growth processes are still unclear.Here,we report a simple way to control the interaction between nanoparticles by manipulating the oleylamine(OAm)adsorbed on the surface of the nanoparticles.The size distributions of Ag nanoparticles produced at different reaction pressures were monitored as evidence for aggregative growth.From these kinetic data,the aggregative nucleation rate(C)of primary Ag nanoparticles under a 0.01 MPa was demonstrated to be faster than that under atmospheric pressure.This leads to a higher uniformity of Ag nanoparticles in a shorter time(10 min)than that achievable with previous methods.Furthermore,Ag nanoparticles supported on TiO2 exhibited a remarkable performance in the catalytic reduction of 4-nitrophenol(4-NP).After 4 min,4-NP was completely reduced into4-aminophenol(4-AP).展开更多
基金financially supported by National Natural Science Foundation of China(Nos.21922602,22076047 and U21A20326)Shanghai Science and Technology Innovation Action Plan(No.20dz1204200)the Fundamental Research Funds for the Central Universities。
文摘Designing metal compounds based on their structure and chemical composition is essential in achieving desirable performance in methane oxidation,because of the synergistic effect between different metal elements.Herein,a bimetallic Ru-Pt catalyst on TiO_(2) support(RuPt-O/TiO_(2)) was prepared by in situ reduction followed by calcination in air.Compared with monometallic catalysts(Ru-O/TiO_(2) and Pt-O/TiO_(2)),the synergistic effect of mixed metals endowed bimetallic catalysts with excellent stability and outstanding performance in methane oxidation,with a reaction rate of 13.9×10^(-5)mol^(-1)_(CH_(4))·g^(-1)_(Ru+Pt)·s^(-1)at 303℃.The varied characterization results revealed that among the bimetallic catalysts,RuO_(2)was epitaxially grown on the TiO_(2) substrate owing to lattice matching between them,and part of the PtO_(x) adhered to the RuO_(2) surface,in addition to a single PtO_(x) nanoparticle with 4 nm in size.Consequently,Pt mainly existed in the form of Pt2+and Pt4+and a small amount of zero valence in the bimetallic catalyst,prompting the adsorption and activation of methane as the first and rate-controlling step for CH_(4) oxidation.More importantly,the RuO_(2) species provided additional oxygen species to facilitate the redox cycle of the PtO_(x) species.This study opens a new route for structurally designing promising catalysts for CH4oxidation.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFC0204300)the National Natural Science Foundation of China (Nos. 21577034 and 21333003)the Science and Technology Commission of Shanghai Municipality (No. 16ZR1407900)
文摘A series of Cu-SSZ-13 catalysts with the same Cu loading were prepared by different methods of incipient wetness impregnation [Cu-SSZ-13(IWI)], ion exchange[Cu-SSZ-13(IE)] and hydro-thermal synthesis [Cu-SSZ-13(HTS)]. Their activity for selective catalytic reduction of nitrogen oxides(NO_x) with NH3 was determined. The results show that the Cu-SSZ-13(HTS) catalyst exhibits a better ammonia selective catalytic reduction(NH3-SCR)activity compared with the other two catalysts, over which more than 90% NO conversion is obtained at 215-600℃under the space velocity of 180,000 h^(-1). The characterization results reveal that the Cu-SSZ-13(HTS) catalyst possesses more amount of stable Cu^(2+) in the six-membered ring and high ability for NH3 and NO adsorption, leading to its high NH3-SCR activity, although this catalyst has low surface area. On the other hand, the activity of Cu-SSZ-13(IE) catalyst is almost the same as that of Cu-SSZ-13(IWI) catalyst at the temperature lower than 400 ℃, but the activity of the former is much higher than that of the latter at > 400 ℃ due to the high activity of Cu-SSZ-13(IWI) catalyst for NH3 oxidation.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFC0204300)the National Key Basic Research Program of China (No. 2013CB933200)Science and Technology Commission of Shanghai Municipality (No. 16ZR1407900)
文摘A series of 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2 catalysts were prepared by impregnation method based on the presynthesis of Sn_(0.9)Ce_(0.1)O_2 support prepared by co-precipitation method, and then characterized by Brunauer–Emmett–Teller(BET), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Raman, CO chemical adsorption and hydrogen temperature-programmed reduction(H_2-TPR) techniques. The effect of calcination temperature of the composite oxide support on the catalytic performances of the Pd/Sn_(0.9)Ce_(0.1)O_2 catalyst for the CH_4 total oxidation was studied. It is found that the catalytic activity of the Pd/Sn_(0.9)Ce_(0.1)O_2 catalyst increases with the increase in calcination temperature of the Pd/Sn_(0.9)Ce_(0.1)O_2 support. The 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2/1100 catalyst(the Pd/Sn_(0.9)Ce_(0.1)O_2 support was calcined at 1100 ℃) exhibits the best reactive activity(T_(10)= 255 ℃). The excellent activity of the 0.2 wt% Pd/Sn_(0.9)Ce_(0.1)O_2/1100 catalyst should be attributed to the high reducibility of PdO, the excellent oxygen mobility of the support and the high content of active Pd^(2+) species on the Pd/Sn_(0.9)Ce_(0.1)O_2 catalyst.
基金financially supported by the National Basic Research Program of China (No. 2010CB732300)
文摘The unsupported Cu and Ag catalysts with different oxidation states were prepared, and their catalytic performances for propylene epoxidation were investigated.The metallic Cu catalyst exhibits much higher catalytic activity and propylene oxide(PO) selectivity than Cu2 O and Cu O catalysts.The Cu0 species are the main active sites for propylene epoxidation, but Cu2 O and Cu O species are in favor of CO2 and acrolein production.The PO selectivity of 54.2 % and propylene conversion of 2.6 % can be achieved over the metallic Cu catalyst at 160 °C in initial stage, but metallic Cu catalyst would be oxidized to Cu2 O during propylene epoxidation, resulting in a sharp decrease in the PO selectivity and propylene conversion.Nanosize Ag Cuxbimetallic catalysts were prepared.It is found that adding Ag to the metallic Cu catalysts can prevent the oxidation of Cu and make Ag Cuxbimetallic catalysts more stable under the condition of propylene epoxidation.The Ag/Cu molar ratio can remarkably affect the catalytic performance of Ag Cuxcatalyst and the selectivity to PO and acrolein.After Ag Cuxwas supported on MOx-modified a-Al2O3, its catalytic performance can be improved and has a close relationship with the acid–base property of support.
基金financially supported by the National Key Research and Development Program of China(No.2016YFC0204300)the National Natural Science Foundation of China(Nos.21571061,21333003 and 21908079)Pujiang Program of the Shanghai Municipal Human Resources and Social Security Bureau(No.18PJD011)。
文摘Development of active and stable catalysts for low-temperature CO oxidation has long been regarded as a hot topic.In this contribution,we used CeO_(2) with high-density surface pits as support to prepare an active and stable Au/CeO_(2) catalyst by an adsorption-deposition method.The obtained 0.05 wt%Au/CeO_(2)-TD(where TD represents thermal decomposition)can maintain its activity at 80℃ for more than 20 h or even after calcination at 800℃ for 2 h.The characterization results showed that the high-density surface pits on CeO_(2)-TD play a decisive role in the stabilization of Au and enhancement of the redox property.This work may provide a new strategy to improve the stability of supported metal catalysts by a simple and conventional method.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFC0204300)the National Natural Science Foundation of China (Nos.21922602 and 21577034)Fundamental Research Funds for the Central Universities (No.222201717003)。
文摘Au-Cu bimetallic nanoparticles with uniform size,shape,and compositions were synthesized by wet chemistry method,and then the Au-Cu/SiO_(2) catalyst supported on SiO_(2) was prepared.Meanwhile,their catalytic activity for the selective oxidation of propene to acrolein using O_(2) as an oxidant was evaluated.The bimetallic catalyst shows a significantly enhanced catalytic performance comparing with Au and Cu monometallic catalysts.Characterization of the materials and kinetic study was conducted to explore the cooperating mechanism of Au and Cu for improving the catalytic activity of the bimetallic catalyst.Cu component can segregate to the alloy surface and the Au-Cu alloy transferred to Au-CuO core/shell structure after annealing during the preparation process.Based on the Mars-van Krevelen mechanism for the selective oxidation of propene over the prepared catalysts,the coexistence of CuO can promote the adsorption and activation of O_(2).Meanwhile,the electrons transfer from Au to Cu in the catalyst can facilitate the adsorptions of both oxygen on CuO sites and propene on Au sites.The combined effects of the above two aspects result in the high catalytic activity of the Au-Cu/SiO_(2) catalyst for selective oxidation of propene to acrolein,compared to the Au/SiO_(2) and CuO/SiO_(2) catalysts.
基金financially supported by the National Key Research and Development Program of China(No.2016YFC0204300)the National Natural Science Foundation of China(Nos.21922602 and 21577035)the Fundamental Research Funds for the Central Universities(No.222201717003)。
文摘A series of Co_(3) O_(4) catalysts was prepared by ammonia(Co-AP) and oxalate(Co-OP) precipitation,solgel(Co-SG),and urea hydrothermal(Co-UH) methods,and their physicochemical properties were characterised by numerous techniques including X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nitrogen sorption,X-ray photoelectron spectroscopy(XPS),temperature-programmed reduction of H_(2)(H_(2)-TPR),temperature-programmed desorption of O_(2)(O_(2)-TPD),and temperature-programmed desorption of NH_(3)(NH_(3)-TPD).The catalytic activity of each catalyst was estimated for the catalytic combustion of vinyl chloride(VC) emissions.The crystallite size of the Co_(3) O_(4) catalyst was found to be well correlated with the amounts of surface-adsorbed oxygen species and number of acid sites on the catalyst surface,and consequently,determined several physicochemical properties of the catalyst.Of the catalysts studied here,the Co-AP catalyst exhibits the smallest crystallite size,which increases the specific surface area and the concentration of Co^(2+) on the catalyst surface.This,in turn,enhances the redox property,oxygen mobility,and the number of acid sites associated with the Co-AP catalyst.In fact,the Co-AP catalyst exhibits the best catalytic activity for VC combustion at 360℃and does not produce any chlorinated by-products.
基金the Shanghai Pujiang Program(No.17PJD012)the Science and Technology Commission of Shanghai Municipality(No.16ZR1407900)。
文摘Recent studies suggested that the interactions between particles can induce aggregative nucleation and growth processes beyond those predicted by the traditional LaMer model of nanoparticle formation,but their nucleation and growth processes are still unclear.Here,we report a simple way to control the interaction between nanoparticles by manipulating the oleylamine(OAm)adsorbed on the surface of the nanoparticles.The size distributions of Ag nanoparticles produced at different reaction pressures were monitored as evidence for aggregative growth.From these kinetic data,the aggregative nucleation rate(C)of primary Ag nanoparticles under a 0.01 MPa was demonstrated to be faster than that under atmospheric pressure.This leads to a higher uniformity of Ag nanoparticles in a shorter time(10 min)than that achievable with previous methods.Furthermore,Ag nanoparticles supported on TiO2 exhibited a remarkable performance in the catalytic reduction of 4-nitrophenol(4-NP).After 4 min,4-NP was completely reduced into4-aminophenol(4-AP).
