Globin-like mesoporous CeO2 has been constructed by using a CO-assisted synthetic approach based on hydroxide carbonate precursors, in which CO plays a key role in the formation of the globin-like mesoporous precursor...Globin-like mesoporous CeO2 has been constructed by using a CO-assisted synthetic approach based on hydroxide carbonate precursors, in which CO plays a key role in the formation of the globin-like mesoporous precursors as the carbon source because of its preferential adsorption on Ce^3＋ under the hydrothermal conditions. The formation mechanism and the thermal transformation process from globin-like mesoporous CeCO3OH to CeO2 have been investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, BET surface area measurements, thermal analysis, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy and X-ray photoelectron spec- troscopy. Rod-like building blocks interconnected by nanoparticles circle around to form each globin-like CeO2 spheres, leading to the formation of a mesoporous structure. The globin-like mesoporous CeO2 shows much better performance in CO catalytic oxidation than ordinary CeO2 nanoparticles obtained by directly calcining cerium nitrate. Moreover, the globin-like mesoporous CeO2 can act as an ideal matrix for supported catalysts. Metallic Au particles can be well dispersed in the globin-like CeO2 matrix to form Au/CeO2 supported catalysts, which exhibit excellent activity for CO oxidation at room temperature.展开更多
In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at%and 3.2 at%)was introduced to the ceria nanorods via a deposition-precipitation(DP)approach,and copper species of ca.10 at%were sequentially a...In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at%and 3.2 at%)was introduced to the ceria nanorods via a deposition-precipitation(DP)approach,and copper species of ca.10 at%were sequentially anchored onto the modified ceria support by a similar DP route.The aim of the study was to investigate the effect of the amount of tungsten oxide(0,0.4 at%,2.0 at%,and 3.2 at%)modifier on the copper-ceria catalysts for CO oxidation reaction and shed light on the structure-activity relationship.By the aids of multiple characterization techniques including N2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H2-TPR)in combination with the catalytic performance for CO oxidation reaction,it is found that the copper-ceria samples maintain the crystal structure of the fluorite fcc CeO2 phase with the same nanorod-like morphology with the introduction of tungsten oxide,while the textural properties(the surface area,pore volume and pore size)of ceria support and copper-ceria catalysts are changed,and the oxidation states of copper and tungsten are kept the same as Cu2+and W6+before and after the reaction,but the introduction of tungsten oxide(WO3)significantly changes the metal-support interaction(transfer the CuOx clusters to Cu-[Ox]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.展开更多
The chemical looping reforming of methane through the nonstoichiometric ceria redox cycle(CeO2/CeO2-δ) has been experimentally investigated in a directly irradiated solar reactor to convert both solar energy and meth...The chemical looping reforming of methane through the nonstoichiometric ceria redox cycle(CeO2/CeO2-δ) has been experimentally investigated in a directly irradiated solar reactor to convert both solar energy and methane to syngas in the temperature range 900–1050 °C. Experiments were carried out with different ceria shapes via two-step redox cycling composed of endothermic partial reduction of ceria with methane and complete exothermic re-oxidation of reduced ceria with H2 O/CO2 at the same operating temperature, thereby demonstrating the capability to operate the cycle isothermally. A parametric study considering different ceria macrostructure variants(ceria packed powder, ceria packed powder mixed with inert Al2 O3 particles, and ceria reticulated porous foam) and operating parameters(methane flow-rate, reduction temperature, or sintering temperature) was conducted in order to unravel their impact on the bed-averaged oxygen non-stoichiometry(δ), syngas yield, methane conversion, and solar reactor performance. The ceria cycling stability was also experimentally investigated to demonstrate repeatable syngas production by alternating the flow between CH4 and H2 O(or CO2). A decrease in sintering temperature of the ceria foam was beneficial for increasing syngas selectivity, methane conversion,and reactor performance. Increasing both CH4 concentration and reduction temperature enhanced δ with the maximum value up to 0.41 but concomitantly favored CH4 cracking reaction. The ceria reticulated porous foam showed better performance in terms of effective heat transfer, due to volumetric absorption of concentrated solar radiation and uniform heating with lower solar power consumption, thereby promoting the solar-to-fuel energy conversion efficiency that reached up to 5.60%. The energy upgrade factor achieved during cycle was up to 1.19. Stable patterns in the δ and syngas yield for consecutive cycles with the ceria foam validated material performance stability.展开更多
The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies ...The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies on the(110) surface of CeO_2 have been studied combining aberration-corrected transmission electron microscopy and first-principles calculations. The oxygen adatoms were estimated to be located on top of Ce atoms with 50% coverage, forming a c(2×2) reconstruction. The oxygen vacancies can form stable configuration, with the Ce atoms partly reduced.展开更多
Three La-doped CeO2-ZrO2-Al2O3(CZA)composite oxide samples,namely,CZA-I,CZA-II and CZA-III,were prepared following a co-precipitation method in the presence of La2O3,La(NO3)3-6H2O and H[La(EDTA)]-16H2O precursors,resp...Three La-doped CeO2-ZrO2-Al2O3(CZA)composite oxide samples,namely,CZA-I,CZA-II and CZA-III,were prepared following a co-precipitation method in the presence of La2O3,La(NO3)3-6H2O and H[La(EDTA)]-16H2O precursors,respectively.When the precursor samples are sintered at 1000°C,the as-prepared composite oxides mainly exhibit the CeO2-ZrO2 cubic fluorite phase,while theγ-Al2O3 andδ-Al2O3 phases appear when the precursor samples are subjected to sintering at 1100 and 1200°C.CZA-III exhibits improved redox properties after high-temperature treatment compared with CZA-I and CZA-II.CZA-III presents the largest surface area of 97.46 m2/g among the three CZAs when the CZA-III precursor sample is sintered at 1000°C.Furthermore,the corresponding oxygen storage capacity(OSC)is the largest with value of 400.27μmol/g when CZA-III precursor sample is sintered at 1000°C.Additionally,CZA-III exhibits the best thermal stability and the highest reduction temperature.However,by increasing the sintering temperature to 1200°C,there is a dramatic decline in the properties of surface area and OSC.And a decrease for CZA-III in surface area by 58.94%and a decrease of the OSC value by 74.56%are observed.展开更多
Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidatio n.However,the electron state of active metal center is still an open question.In this work,a ce ria nanorod s...Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidatio n.However,the electron state of active metal center is still an open question.In this work,a ce ria nanorod support was prepared and platinum(Pt)with 0.9 at%was deposited using an impregnation method to obtain Pt/CeO_(2)catalyst.With the help of"light-off"experiment and temperatureprogrammed reduction under CO(CO-TPR)test,the conclusion is proposed that the process of hydrogen reduction can enhance the activity of CO oxidation reaction for the generation of optimal active Pt site.An innovative near-situ X-ray absorption fine structure(XAFS)technique was used to investigate the chemical state of central Pt atom during the reaction process,clearly demonstrating that the high oxidized state of Pt does harm to the activity for CO oxidation while the relatively reductive Pt exhibits high activity,and the different oxidized state and chemical environment of Pt during every process has been identified.Furthermore,the activity of our Pt/CeO_(2)catalyst is superior to that of most of the previous reports about CO catalytic oxidation by Pt based catalyst.Moreover,the optimal active species(Pt-O_(4))have been identified after hydrogen reduction,which could be a possible key strategy to control the oxidation of Pt.展开更多
Ag nanoparticles grown on reduced CeO2-x thin films have been studied by X-ray plhotoelec- tron spectroscopy and resonant photoelectron spectroscopy of the valence band to understand the effect of oxygen vacancies in ...Ag nanoparticles grown on reduced CeO2-x thin films have been studied by X-ray plhotoelec- tron spectroscopy and resonant photoelectron spectroscopy of the valence band to understand the effect of oxygen vacancies in the CeO2-x thin films on the growth and interracial elec- tronic properties of Ag. Ag grows as three-dimensional particles on the CeO2-x （111） surface at 300 K. Compared to the fully oxidized ceria substrate surface, Ag favors the growth of smaller particles with a larger particle density on the reduced ceria substrate surface, which can be attributed to the nucleation of Ag on oxygen vacancies. The binding energy of Ag3d increases when the Ag particle size decreases, which is mainly attributed to the final-state screening. The interracial interaction between Ag and CeO2_x（lll） is weak. The resonant enhancement of the 4f level of Ce3＋ species in RPES indicates a partial Ce4＋--＋Ce3＋ reduction after Ag deposited on reduced ceria surface. The sintering temperature of Ag on CeO 1.85 （111） surface during annealing is a little higher than that of Ag on CeO2 （111） surface, indicating that Ag nanoparticles are more stable on the reduced ceria surface.展开更多
Copper-ceria sheets catalysts with different loadings of copper（2 wt.%, 5 wt.% and 10 wt.%） supported on ceria nanosheets were synthesized via a depositioneprecipitation（DP） method. The prepared catalysts were sys...Copper-ceria sheets catalysts with different loadings of copper（2 wt.%, 5 wt.% and 10 wt.%） supported on ceria nanosheets were synthesized via a depositioneprecipitation（DP） method. The prepared catalysts were systematically characterized with various structural and textural detections including X-ray diffraction（XRD）, Raman spectra, transmission electron microscopy（TEM）, X-ray absorption fine structure（XAFS）, and temperature-programmed reduction by hydrogen（H2-TPR）, and tested for the CO oxidation reaction. Notably, the sample containing 5 wt.% of Cu exhibited the best catalytic performance as a result of the highest number of active CuO species on the catalyst surface. Further increase of copper content strongly affects the dispersion of copper and thus leads to the formation of less active bulk CuO phase, which was verified by XRD and H2-TPR analysis. Moreover, on the basis of in-situ diffuse reflectance infrared Fourier transform spectroscopy（in-situ DRIFTS） results, the surface Cu~＋ species, which are derived from the reduction of Cu^（2＋）, are likely to play a crucial role in the catalyzing CO oxidation.Consequently, the superior catalytic performance of the copper-ceria sheets is mainly attributed to the highly dispersed CuOx cluster rather than Cu-[Ox]-Ce structure, while the bulk CuO phase is adverse to the catalytic activity of CO oxidation.展开更多
文摘Globin-like mesoporous CeO2 has been constructed by using a CO-assisted synthetic approach based on hydroxide carbonate precursors, in which CO plays a key role in the formation of the globin-like mesoporous precursors as the carbon source because of its preferential adsorption on Ce^3＋ under the hydrothermal conditions. The formation mechanism and the thermal transformation process from globin-like mesoporous CeCO3OH to CeO2 have been investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, BET surface area measurements, thermal analysis, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy and X-ray photoelectron spec- troscopy. Rod-like building blocks interconnected by nanoparticles circle around to form each globin-like CeO2 spheres, leading to the formation of a mesoporous structure. The globin-like mesoporous CeO2 shows much better performance in CO catalytic oxidation than ordinary CeO2 nanoparticles obtained by directly calcining cerium nitrate. Moreover, the globin-like mesoporous CeO2 can act as an ideal matrix for supported catalysts. Metallic Au particles can be well dispersed in the globin-like CeO2 matrix to form Au/CeO2 supported catalysts, which exhibit excellent activity for CO oxidation at room temperature.
基金Project supported by National Natural Science Foundation of China(21773288,51902093)National Key Basic Research Program of China(2017YFA0403402)。
文摘In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at%and 3.2 at%)was introduced to the ceria nanorods via a deposition-precipitation(DP)approach,and copper species of ca.10 at%were sequentially anchored onto the modified ceria support by a similar DP route.The aim of the study was to investigate the effect of the amount of tungsten oxide(0,0.4 at%,2.0 at%,and 3.2 at%)modifier on the copper-ceria catalysts for CO oxidation reaction and shed light on the structure-activity relationship.By the aids of multiple characterization techniques including N2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H2-TPR)in combination with the catalytic performance for CO oxidation reaction,it is found that the copper-ceria samples maintain the crystal structure of the fluorite fcc CeO2 phase with the same nanorod-like morphology with the introduction of tungsten oxide,while the textural properties(the surface area,pore volume and pore size)of ceria support and copper-ceria catalysts are changed,and the oxidation states of copper and tungsten are kept the same as Cu2+and W6+before and after the reaction,but the introduction of tungsten oxide(WO3)significantly changes the metal-support interaction(transfer the CuOx clusters to Cu-[Ox]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.
基金The King Mongkut’s Institute of Technology Ladkrabang(KMITL),Thailandthe Franco-Thai scholarship program。
文摘The chemical looping reforming of methane through the nonstoichiometric ceria redox cycle(CeO2/CeO2-δ) has been experimentally investigated in a directly irradiated solar reactor to convert both solar energy and methane to syngas in the temperature range 900–1050 °C. Experiments were carried out with different ceria shapes via two-step redox cycling composed of endothermic partial reduction of ceria with methane and complete exothermic re-oxidation of reduced ceria with H2 O/CO2 at the same operating temperature, thereby demonstrating the capability to operate the cycle isothermally. A parametric study considering different ceria macrostructure variants(ceria packed powder, ceria packed powder mixed with inert Al2 O3 particles, and ceria reticulated porous foam) and operating parameters(methane flow-rate, reduction temperature, or sintering temperature) was conducted in order to unravel their impact on the bed-averaged oxygen non-stoichiometry(δ), syngas yield, methane conversion, and solar reactor performance. The ceria cycling stability was also experimentally investigated to demonstrate repeatable syngas production by alternating the flow between CH4 and H2 O(or CO2). A decrease in sintering temperature of the ceria foam was beneficial for increasing syngas selectivity, methane conversion,and reactor performance. Increasing both CH4 concentration and reduction temperature enhanced δ with the maximum value up to 0.41 but concomitantly favored CH4 cracking reaction. The ceria reticulated porous foam showed better performance in terms of effective heat transfer, due to volumetric absorption of concentrated solar radiation and uniform heating with lower solar power consumption, thereby promoting the solar-to-fuel energy conversion efficiency that reached up to 5.60%. The energy upgrade factor achieved during cycle was up to 1.19. Stable patterns in the δ and syngas yield for consecutive cycles with the ceria foam validated material performance stability.
基金supported by the National Natural Science Foundation of China (11079033)National Basic Research Program of China (973 Program, 2013CB933104, 2010CB923301)Fundamental Research Funds for the Central Universities (WK2060030005)~~
基金supported by the National Natural Science Foundation of China(Grant Nos.51525102,51390475,51371102&21673277)National Basic Research Program of China(Grant No.2015CB654902)
文摘The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies on the(110) surface of CeO_2 have been studied combining aberration-corrected transmission electron microscopy and first-principles calculations. The oxygen adatoms were estimated to be located on top of Ce atoms with 50% coverage, forming a c(2×2) reconstruction. The oxygen vacancies can form stable configuration, with the Ce atoms partly reduced.
基金Project(14JJ4043)supported by the Natural Science Foundation of Hunan Province,China
文摘Three La-doped CeO2-ZrO2-Al2O3(CZA)composite oxide samples,namely,CZA-I,CZA-II and CZA-III,were prepared following a co-precipitation method in the presence of La2O3,La(NO3)3-6H2O and H[La(EDTA)]-16H2O precursors,respectively.When the precursor samples are sintered at 1000°C,the as-prepared composite oxides mainly exhibit the CeO2-ZrO2 cubic fluorite phase,while theγ-Al2O3 andδ-Al2O3 phases appear when the precursor samples are subjected to sintering at 1100 and 1200°C.CZA-III exhibits improved redox properties after high-temperature treatment compared with CZA-I and CZA-II.CZA-III presents the largest surface area of 97.46 m2/g among the three CZAs when the CZA-III precursor sample is sintered at 1000°C.Furthermore,the corresponding oxygen storage capacity(OSC)is the largest with value of 400.27μmol/g when CZA-III precursor sample is sintered at 1000°C.Additionally,CZA-III exhibits the best thermal stability and the highest reduction temperature.However,by increasing the sintering temperature to 1200°C,there is a dramatic decline in the properties of surface area and OSC.And a decrease for CZA-III in surface area by 58.94%and a decrease of the OSC value by 74.56%are observed.
基金Project supported by Shanghai Large Scientific Facilities CenterNational Key Basic Research Program of China(2017YFA0403402)+1 种基金the National Natural Science Foundation of China(U1932119)This work was also supported by Shanghai Large Scientific Facilities Center.
文摘Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidatio n.However,the electron state of active metal center is still an open question.In this work,a ce ria nanorod support was prepared and platinum(Pt)with 0.9 at%was deposited using an impregnation method to obtain Pt/CeO_(2)catalyst.With the help of"light-off"experiment and temperatureprogrammed reduction under CO(CO-TPR)test,the conclusion is proposed that the process of hydrogen reduction can enhance the activity of CO oxidation reaction for the generation of optimal active Pt site.An innovative near-situ X-ray absorption fine structure(XAFS)technique was used to investigate the chemical state of central Pt atom during the reaction process,clearly demonstrating that the high oxidized state of Pt does harm to the activity for CO oxidation while the relatively reductive Pt exhibits high activity,and the different oxidized state and chemical environment of Pt during every process has been identified.Furthermore,the activity of our Pt/CeO_(2)catalyst is superior to that of most of the previous reports about CO catalytic oxidation by Pt based catalyst.Moreover,the optimal active species(Pt-O_(4))have been identified after hydrogen reduction,which could be a possible key strategy to control the oxidation of Pt.
文摘Ag nanoparticles grown on reduced CeO2-x thin films have been studied by X-ray plhotoelec- tron spectroscopy and resonant photoelectron spectroscopy of the valence band to understand the effect of oxygen vacancies in the CeO2-x thin films on the growth and interracial elec- tronic properties of Ag. Ag grows as three-dimensional particles on the CeO2-x （111） surface at 300 K. Compared to the fully oxidized ceria substrate surface, Ag favors the growth of smaller particles with a larger particle density on the reduced ceria substrate surface, which can be attributed to the nucleation of Ag on oxygen vacancies. The binding energy of Ag3d increases when the Ag particle size decreases, which is mainly attributed to the final-state screening. The interracial interaction between Ag and CeO2_x（lll） is weak. The resonant enhancement of the 4f level of Ce3＋ species in RPES indicates a partial Ce4＋--＋Ce3＋ reduction after Ag deposited on reduced ceria surface. The sintering temperature of Ag on CeO 1.85 （111） surface during annealing is a little higher than that of Ag on CeO2 （111） surface, indicating that Ag nanoparticles are more stable on the reduced ceria surface.
基金Project supported by the National Natural Science Foundation of China(21301107,21501109)the Excellent Young Scientists Fund from NSFC(21622106)+3 种基金the Taishan Scholar Project of Shandong Province of China,China Postdoctoral Science Foundation(2014M551891,2015T80706)Doctoral Funding of Shandong Province of China(BS2014CL008)Specialized Research Fund for the Doctoral Program of Higher Education(20130131120009)Postdoctoral Innovation Project Foundation of Shandong Province(201301008)
文摘Copper-ceria sheets catalysts with different loadings of copper（2 wt.%, 5 wt.% and 10 wt.%） supported on ceria nanosheets were synthesized via a depositioneprecipitation（DP） method. The prepared catalysts were systematically characterized with various structural and textural detections including X-ray diffraction（XRD）, Raman spectra, transmission electron microscopy（TEM）, X-ray absorption fine structure（XAFS）, and temperature-programmed reduction by hydrogen（H2-TPR）, and tested for the CO oxidation reaction. Notably, the sample containing 5 wt.% of Cu exhibited the best catalytic performance as a result of the highest number of active CuO species on the catalyst surface. Further increase of copper content strongly affects the dispersion of copper and thus leads to the formation of less active bulk CuO phase, which was verified by XRD and H2-TPR analysis. Moreover, on the basis of in-situ diffuse reflectance infrared Fourier transform spectroscopy（in-situ DRIFTS） results, the surface Cu~＋ species, which are derived from the reduction of Cu^（2＋）, are likely to play a crucial role in the catalyzing CO oxidation.Consequently, the superior catalytic performance of the copper-ceria sheets is mainly attributed to the highly dispersed CuOx cluster rather than Cu-[Ox]-Ce structure, while the bulk CuO phase is adverse to the catalytic activity of CO oxidation.
