Transference of CuO species and thermal solid-solid interaction in CuO/CeO2-Al2O3 catalyst prepared by an impregnation method were characterized by in-situ XRD, Raman spectroscopy and H2-TPR techniques. For the cataly...Transference of CuO species and thermal solid-solid interaction in CuO/CeO2-Al2O3 catalyst prepared by an impregnation method were characterized by in-situ XRD, Raman spectroscopy and H2-TPR techniques. For the catalyst calcined at 300℃, two kinds of CuO species coexist on the surface, that is, highly dispersed and bulk CuO crystalline phase. Four kinds of CuO species are present for the catalyst calcined at 600 ℃, ： （1） highly dispersed CuO, （2） bulk CuO on the surface, （3） bulk CuO in the internal layer of CeO2, and （4） CuAl2O4 formed from CuO-Al2O3 interaction. For the catalyst calcined at 800 ℃,C, besides very little highly dispersed and bulk CuO on the surface, most of the CuO has transferred into the internal layer of CeO2 and the mass of CuAl2O4 are increased. At 900 ℃,, all of CuO has diffused into the internal layer of CeO2 and formed CuAl2O4. The results show that the distribution of CuO species in the catalysts depends on the calcination temperature; the different CuO species can be effectively confirmed by in-situ XRD, Raman spectroscopy and H2-TPR techniques.展开更多
The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO2 and Pt/SiC catalysts were successfully prepared via a ...The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt0 on the support surface,as evidenced by the appearance of Pt2+species.It is consistent with the XPS data of Pt/CeO2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of catalytic activity.展开更多
Elucidation of the CuOx-CeO2 interactions is of great interest and importance in understanding complex CuOx-CeO2 interfacial catalysis in various reactions. In the present work, we have investigated structures and cat...Elucidation of the CuOx-CeO2 interactions is of great interest and importance in understanding complex CuOx-CeO2 interfacial catalysis in various reactions. In the present work, we have investigated structures and catalytic activity in CO oxidation of CuOx species on CeO2 rods, cubes and polyhedra predominantly exposing {110}+{100}, {100} and {111} facets by the incipient wetness impregnation method with the lowest Cu loading of 0.025%. The structural evolution of CuOx species was found to depend on both the Cu loading and the CeO2 morphology. As the Cu loading increases, CuOx species are deposited preferentially on the surface defect of CeO2 and then aggregate and grow, accompanied by the formation of isolated Cu ions, CuOx clusters strongly/weakly interacting with the CeO2, highly dispersed Cu O nanoparticles, and large Cu O nanoparticles. The isolated Cu^+ species and CuOx clusters weakly interacting with the CeO2 were observed mainly on the O-terminated CeO2{100} facets. Meanwhile, more Cu(I) species are stabilized during CO reduction processes in CuOx/c-CeO2 catalysts than in CuOx/r-CeO2 and CuOx/p-CeO2 catalysts. The catalytic activities of various CuOx/CeO2 catalysts in CO oxidation vary with both the CuOx species and the CeO2 morphology. These results comprehensively elucidate the CuOx-CeO2 interactions and exemplify their morphology-dependence.展开更多
This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature....This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation,hydrothermal treatment, co‐precipitation, and a sol‐gel technique, were used to synthesizeMnOx‐CeO2 catalysts. The catalysts were characterized in detail, and an NH3‐SCR model reaction waschosen to evaluate the catalytic performance. The results showed that the preparation methodsaffected the catalytic performance in the order: hydrothermal treatment > sol‐gel > co‐precipitation> impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content,oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sitesand acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalystformed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalyticperformance, and good H2O resistance in NH3‐SCR reaction. This was attributed to incorporationof Mnn+ into the CeO2 lattice to form a uniform ceria‐based solid solution (containing Mn‐O‐Cestructures). Strengthening of the electronic interactions between MnOx and CeO2, driven by thehigh‐temperature and high‐pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment‐friendly route to synthesizing low‐temperature denitrification (deNOx) catalysts.展开更多
Precious metal-support interaction plays an important role in thermal stability and catalytic performance of the automotive exhaust catalysts. The support is not only a cartier for active compotmds in catalysts but al...Precious metal-support interaction plays an important role in thermal stability and catalytic performance of the automotive exhaust catalysts. The support is not only a cartier for active compotmds in catalysts but also can improve the dispersion of precious metals and suppress the sintering of precious metals at high temperature; meanwhile, noble metals can also enhance the redox performance and oxygen storage capacity of support. The mechanism of metal-support interactions mainly includes electronic interaction, formation of alloy and inward diffusion of metal into the support or covered by support. The form and degree of precious metal-sup- port interaction depend on many factors, including the content of precious metal, the species of support and metal, and preparation methods. The research results about strong metal-support interaction （SMSI） gave a theory support for developing a kind of new cata- lyst with excellent performance. This paper reviewed the interaction phenomenon and mechanism of precious metals （Pt, Pd, Rh） and support such as A1203, CeO2, and CeO2-based oxides in automotive exhaust catalysts. The factors that affect SMSI and the catalysts developed by SMSI were also discussed.展开更多
A series of CeO2-ZrO2-WO3 catalysts for the selective catalytic reduction （SCR） of NO with NH3 were prepared by hydrothermal method. The influence of calcination temperature on the catalytic activity, microstructure...A series of CeO2-ZrO2-WO3 catalysts for the selective catalytic reduction （SCR） of NO with NH3 were prepared by hydrothermal method. The influence of calcination temperature on the catalytic activity, microstructure, surface acidity and redox behavior of CeO2-ZrO2-WO3 catalyst was investigated using various characterization methods. It was found that the CeO2-ZrO2-WO3 catalyst calcined at 600 ℃ showed the best catalytic performance and excellent N2 selectivity, and yielded more than 90% NO conversion in a wide temperature range of 250-500 ℃ with a space velocity （GHSV） of 60000 131. As the calcination temperature was increased from 400 to 600 ℃, the NO conversion obviously increased, but decreased at higher calcination temperature. The results implied that the higher surface area, the strongest synergistic interaction, the superior redox property and the highly dispersed or amorphous WO3 species contributed to the excellent SCR activity of the CeO2-ZrO2-WO3 catalyst calcined at 600℃.展开更多
Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surf...Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surface structures is required.We have thus studied the growth of CeOx nanostructures(NSs)and thin films on Pt(111).The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts.However,the Pt-CeOx interaction has not been understood at the atomic level.We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria,which could subsequently determine their catalytic chemistry.While ceria on Pt(111)typically exposes the CeO2(111)surface,we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures,owing to the electronic interaction between Pt and CeOx.A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111)substrate.For a ceria film of^3–4 monolayer(ML)thickness on Pt(111),annealing in ultrahigh vacuum(UHV)at 1000 K results in a surface of CeO2(100),stabilized by a c-Ce2O3(100)buffer layer.Further oxidation at 900 K transforms the surface of the CeO2(100)thin film into a hexagonal CeO2(111)surface.展开更多
We report a facile electroless chemical deposition(ECD)method to deposit uniform Pd nanoparticles((2.5±0.6)nm)on CeO2 nanorods(PdNPs/CeO2-ECD)through the interface redox reaction between the reduced CeO2 and Na2P...We report a facile electroless chemical deposition(ECD)method to deposit uniform Pd nanoparticles((2.5±0.6)nm)on CeO2 nanorods(PdNPs/CeO2-ECD)through the interface redox reaction between the reduced CeO2 and Na2PdCl4.Pd NPs/CeO2-ECD exhibits a stronger electronic metal-support interaction(EMSI)evidenced by higher reducibility and stronger anti-sintering capability at high temperatures,compared to that prepared by the conventional impregnation method.Such an EMSI effect of PdNPs/CeO2-ECD significantly improves its catalytic activity in CO oxidation.Besides,the chlorine residue-free catalysts through ECD process avoid the deleterious effect of chlorine on CO oxidation.This ECD process can further be extended to deposit various uniform nanoscaled noble metals(Au,Ag,Pt,Ru,Rh,etc.)on CeO2,which may deliver their potentials in advanced catalysis.展开更多
TWC-equipped exhausts are widely used in gasoline-fueled vehicles to meet stringent emission regulations. The main components in TWCs are precious metals such as palladium (Pd), platinum (Pt), and rhodium (Rh) as the ...TWC-equipped exhausts are widely used in gasoline-fueled vehicles to meet stringent emission regulations. The main components in TWCs are precious metals such as palladium (Pd), platinum (Pt), and rhodium (Rh) as the active component, and inorganic oxides such as γ-alumina (Al 2 O 3 ), ceria (CeO 2 ), zirconia (ZrO 2 ) and ceria-zirconia (CeO 2-ZrO 2 ) are used as the support. Interaction of precious metals and support plays an important role in the thermal stability and catalytic performance of TWCs. The support can improve the dispersion of precious metals and suppress the sintering of precious metals at high temperature. In the same, precious metals can also enhance the redox performance and oxygen storage capacity of support. This paper reviews the reaction phenomenon and mechanism of precious metals (Pt, Pd, Rh) and supports such as Al 2 O 3 , CeO 2-based composite oxides.展开更多
XRD and XPS are used to study the dispersion state of CuO on ceria surface.The dispersion capacity values of CuO measured by the two methods are consistent,which are of 1.20 mmol CuO/100 m CeO2.In addition,the results...XRD and XPS are used to study the dispersion state of CuO on ceria surface.The dispersion capacity values of CuO measured by the two methods are consistent,which are of 1.20 mmol CuO/100 m CeO2.In addition,the results reveal that highly dispersed Cu2 + ions are formed at low CuO loadings and that increasing the CuO content to a value higher than its dispersion capacity produces crystalline CuO after the surface vacant sites on CeO2 are filled.The atomic composition of the outermost layer of the CuO/CeO2 samples has been probed by using static secondary ion mass spectroscopy (SSIMS),and the ratios of Cu/Ce are found to be 0.93 and 0.46 for the 1.22 and 0 61 mmol CuO/CeO2 samples respectively.Temperature-programmed reduction (TPR) profile with two reduction peaks at 156 and 16513 suggests that the reduction of highly dispersed Cu2+ ions consists of two steps and is easier than that of CuO crystallites,in which the TPR profile has only one reduction peak at about 249℃.The above experimental results are in good agreement with the prediction of the incorporation model.展开更多
Five hundred ppm Pd/CeO2 catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this rea...Five hundred ppm Pd/CeO2 catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction.Pd/CeO2 catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction.Excellent ethylene selectivity of〜100%was obtained in the whole reaction temperature range of 50℃-200℃ for samples calcined at temperatures of 600℃ and 800℃.This could be ascribed to the formation of PdX-Ce1-xO2-y or Pd-O-Ce surface species based on the X-ray diffiaction and X-ray photoelectron spectroscopy results,indicating the strong interaction between palladium and ceria.展开更多
In the last decades,many reports dealing with technology for the catalytic combustion of methane(CH4)have been published.Recently,attention has increasingly focused on the synthesis and catalytic activity of nickel ox...In the last decades,many reports dealing with technology for the catalytic combustion of methane(CH4)have been published.Recently,attention has increasingly focused on the synthesis and catalytic activity of nickel oxides.In this paper,a NiO/CeO2 catalyst with high catalytic performance in methane combustion was synthe-sized via a facile impregnation method,and its catalytic activity,stability,and water-resistance during CH4 com-bustion were investigated.X-ray diffraction,low-tempera-ture N2 adsorption,thermogravimetric analysis,Fourier transform infrared spectroscopy,hydrogen temperature programmed reduction,methane temperature programmed surface reaction,Raman spectroscopy,electron paramag-netic resonance,and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail.The incorporation of NiO was found to enhance the concentration of oxygen vacancies,as well as the activity and amount of surface oxygen.As a result,the mobility of bulk oxygen in CeO2 was increased.The presence of CeO2 prevented the aggregation of NiO,enhanced reduction by NiO,and provided more oxygen species for the combustion ofCH4.The results of a kinetics study indicated that the reaction order was about 1.07 for CH4 and about 0.10 for O2 over the NiO/CeO2 catalyst.展开更多
Single-atom catalysts (SACs) have recently attracted broad attention in the catalysis field due to their maximized atom efficiency and unique catalytic properties.An atomic-level understanding of the interaction betwe...Single-atom catalysts (SACs) have recently attracted broad attention in the catalysis field due to their maximized atom efficiency and unique catalytic properties.An atomic-level understanding of the interaction between the metal atoms and support is vital for developing stable and high-performance SACs.In this work,Pt1 single atoms with Ioadings up to 4 wt.% were fabricated on ceria nanorods using the atomic layer deposition technique.To understand the Pt-O-Ce bond interfacial interactions,the stability of Pt1 single atoms in the hydrogen reducing environment was extensively investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy CO chemisorption measurements.It was found that ceria defect sites,metal Ioadings and high-temperature calcination are effective ways to tune the stability of Pt1 single atoms in the hydrogen environment.X-ray photoemission spectroscopy further showed that Pt1 single atoms on ceria are dominantly at a +2 valence state at the defect and step edge sites,while those on terrace sites are at a +4 state.The above tailored stability and electronic properties of Pt1 single atoms are found to be strongly correlated with the catalytic activity in the dry and water-mediated CO oxidation reactions.展开更多
文摘Transference of CuO species and thermal solid-solid interaction in CuO/CeO2-Al2O3 catalyst prepared by an impregnation method were characterized by in-situ XRD, Raman spectroscopy and H2-TPR techniques. For the catalyst calcined at 300℃, two kinds of CuO species coexist on the surface, that is, highly dispersed and bulk CuO crystalline phase. Four kinds of CuO species are present for the catalyst calcined at 600 ℃, ： （1） highly dispersed CuO, （2） bulk CuO on the surface, （3） bulk CuO in the internal layer of CeO2, and （4） CuAl2O4 formed from CuO-Al2O3 interaction. For the catalyst calcined at 800 ℃,C, besides very little highly dispersed and bulk CuO on the surface, most of the CuO has transferred into the internal layer of CeO2 and the mass of CuAl2O4 are increased. At 900 ℃,, all of CuO has diffused into the internal layer of CeO2 and formed CuAl2O4. The results show that the distribution of CuO species in the catalysts depends on the calcination temperature; the different CuO species can be effectively confirmed by in-situ XRD, Raman spectroscopy and H2-TPR techniques.
基金Project supported by the National Natural Science Foundation of China(21506194,21676255)the Natural Science Foundation of Zhejiang Province,China(Y16B070025).
文摘The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt0 on the support surface,as evidenced by the appearance of Pt2+species.It is consistent with the XPS data of Pt/CeO2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of catalytic activity.
文摘Elucidation of the CuOx-CeO2 interactions is of great interest and importance in understanding complex CuOx-CeO2 interfacial catalysis in various reactions. In the present work, we have investigated structures and catalytic activity in CO oxidation of CuOx species on CeO2 rods, cubes and polyhedra predominantly exposing {110}+{100}, {100} and {111} facets by the incipient wetness impregnation method with the lowest Cu loading of 0.025%. The structural evolution of CuOx species was found to depend on both the Cu loading and the CeO2 morphology. As the Cu loading increases, CuOx species are deposited preferentially on the surface defect of CeO2 and then aggregate and grow, accompanied by the formation of isolated Cu ions, CuOx clusters strongly/weakly interacting with the CeO2, highly dispersed Cu O nanoparticles, and large Cu O nanoparticles. The isolated Cu^+ species and CuOx clusters weakly interacting with the CeO2 were observed mainly on the O-terminated CeO2{100} facets. Meanwhile, more Cu(I) species are stabilized during CO reduction processes in CuOx/c-CeO2 catalysts than in CuOx/r-CeO2 and CuOx/p-CeO2 catalysts. The catalytic activities of various CuOx/CeO2 catalysts in CO oxidation vary with both the CuOx species and the CeO2 morphology. These results comprehensively elucidate the CuOx-CeO2 interactions and exemplify their morphology-dependence.
基金supported by the National Natural Science Foundation of China (No. 21507130)the Open Project Program of Beijing National Laboratory for Molecular Sciences (No. 20140142)+3 种基金the Open Project Program of Chongqing Key Laboratory of Environmental Materials and Remediation Technology from Chongqing University of Arts and Sciences (No. CEK1405)the Open Project Program of Jiangsu Key Laboratory of Vehicle Emissions Control (No. OVEC001)the Open Project Program of Chongqing Key Laboratory of Catalysis and Functional Organic Molecules from Chongqing Technology and Business University (1456029)the Chongqing Science & Technology Commission (Nos. cstc2016jcyj A0070, cstc2014pt-gc20002, cstckjcxljrc13)~~
文摘This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation,hydrothermal treatment, co‐precipitation, and a sol‐gel technique, were used to synthesizeMnOx‐CeO2 catalysts. The catalysts were characterized in detail, and an NH3‐SCR model reaction waschosen to evaluate the catalytic performance. The results showed that the preparation methodsaffected the catalytic performance in the order: hydrothermal treatment > sol‐gel > co‐precipitation> impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content,oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sitesand acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalystformed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalyticperformance, and good H2O resistance in NH3‐SCR reaction. This was attributed to incorporationof Mnn+ into the CeO2 lattice to form a uniform ceria‐based solid solution (containing Mn‐O‐Cestructures). Strengthening of the electronic interactions between MnOx and CeO2, driven by thehigh‐temperature and high‐pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment‐friendly route to synthesizing low‐temperature denitrification (deNOx) catalysts.
基金supported by National Science & Technology Pillar Program(2012BAE06B00)
文摘Precious metal-support interaction plays an important role in thermal stability and catalytic performance of the automotive exhaust catalysts. The support is not only a cartier for active compotmds in catalysts but also can improve the dispersion of precious metals and suppress the sintering of precious metals at high temperature; meanwhile, noble metals can also enhance the redox performance and oxygen storage capacity of support. The mechanism of metal-support interactions mainly includes electronic interaction, formation of alloy and inward diffusion of metal into the support or covered by support. The form and degree of precious metal-sup- port interaction depend on many factors, including the content of precious metal, the species of support and metal, and preparation methods. The research results about strong metal-support interaction （SMSI） gave a theory support for developing a kind of new cata- lyst with excellent performance. This paper reviewed the interaction phenomenon and mechanism of precious metals （Pt, Pd, Rh） and support such as A1203, CeO2, and CeO2-based oxides in automotive exhaust catalysts. The factors that affect SMSI and the catalysts developed by SMSI were also discussed.
基金Project supported by the National Natural Science Foundation of China(21377048,21307047)the Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education(LYJ1309)
文摘A series of CeO2-ZrO2-WO3 catalysts for the selective catalytic reduction （SCR） of NO with NH3 were prepared by hydrothermal method. The influence of calcination temperature on the catalytic activity, microstructure, surface acidity and redox behavior of CeO2-ZrO2-WO3 catalyst was investigated using various characterization methods. It was found that the CeO2-ZrO2-WO3 catalyst calcined at 600 ℃ showed the best catalytic performance and excellent N2 selectivity, and yielded more than 90% NO conversion in a wide temperature range of 250-500 ℃ with a space velocity （GHSV） of 60000 131. As the calcination temperature was increased from 400 to 600 ℃, the NO conversion obviously increased, but decreased at higher calcination temperature. The results implied that the higher surface area, the strongest synergistic interaction, the superior redox property and the highly dispersed or amorphous WO3 species contributed to the excellent SCR activity of the CeO2-ZrO2-WO3 catalyst calcined at 600℃.
基金supported by the National Key R&D Program of China(2017YFB0602205,2016YFA0202803,2017YFA0303104)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17020200)the National Natural Science Foundation of China(21473191,91545204)~~
文摘Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surface structures is required.We have thus studied the growth of CeOx nanostructures(NSs)and thin films on Pt(111).The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts.However,the Pt-CeOx interaction has not been understood at the atomic level.We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria,which could subsequently determine their catalytic chemistry.While ceria on Pt(111)typically exposes the CeO2(111)surface,we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures,owing to the electronic interaction between Pt and CeOx.A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111)substrate.For a ceria film of^3–4 monolayer(ML)thickness on Pt(111),annealing in ultrahigh vacuum(UHV)at 1000 K results in a surface of CeO2(100),stabilized by a c-Ce2O3(100)buffer layer.Further oxidation at 900 K transforms the surface of the CeO2(100)thin film into a hexagonal CeO2(111)surface.
基金financially supported by the National Natural Science Foundation of China(Nos.21872109 and 61774109)the State Key Laboratory for Mechanical Behavior of Materials(No.20182005)+3 种基金the Hundred Talents Program of Shanxi Provincethe Youth"Sanjin"Scholar Programthe Key R&D Project of Shanxi Province(No.201603D421032)supported by the Cyrus Tang Foundation through Tang Scholar Program。
文摘We report a facile electroless chemical deposition(ECD)method to deposit uniform Pd nanoparticles((2.5±0.6)nm)on CeO2 nanorods(PdNPs/CeO2-ECD)through the interface redox reaction between the reduced CeO2 and Na2PdCl4.Pd NPs/CeO2-ECD exhibits a stronger electronic metal-support interaction(EMSI)evidenced by higher reducibility and stronger anti-sintering capability at high temperatures,compared to that prepared by the conventional impregnation method.Such an EMSI effect of PdNPs/CeO2-ECD significantly improves its catalytic activity in CO oxidation.Besides,the chlorine residue-free catalysts through ECD process avoid the deleterious effect of chlorine on CO oxidation.This ECD process can further be extended to deposit various uniform nanoscaled noble metals(Au,Ag,Pt,Ru,Rh,etc.)on CeO2,which may deliver their potentials in advanced catalysis.
基金National Science technology Support Plan Projects"(2012BAE06B00)
文摘TWC-equipped exhausts are widely used in gasoline-fueled vehicles to meet stringent emission regulations. The main components in TWCs are precious metals such as palladium (Pd), platinum (Pt), and rhodium (Rh) as the active component, and inorganic oxides such as γ-alumina (Al 2 O 3 ), ceria (CeO 2 ), zirconia (ZrO 2 ) and ceria-zirconia (CeO 2-ZrO 2 ) are used as the support. Interaction of precious metals and support plays an important role in the thermal stability and catalytic performance of TWCs. The support can improve the dispersion of precious metals and suppress the sintering of precious metals at high temperature. In the same, precious metals can also enhance the redox performance and oxygen storage capacity of support. This paper reviews the reaction phenomenon and mechanism of precious metals (Pt, Pd, Rh) and supports such as Al 2 O 3 , CeO 2-based composite oxides.
基金supported by the National Natural Science Foundation of China
文摘XRD and XPS are used to study the dispersion state of CuO on ceria surface.The dispersion capacity values of CuO measured by the two methods are consistent,which are of 1.20 mmol CuO/100 m CeO2.In addition,the results reveal that highly dispersed Cu2 + ions are formed at low CuO loadings and that increasing the CuO content to a value higher than its dispersion capacity produces crystalline CuO after the surface vacant sites on CeO2 are filled.The atomic composition of the outermost layer of the CuO/CeO2 samples has been probed by using static secondary ion mass spectroscopy (SSIMS),and the ratios of Cu/Ce are found to be 0.93 and 0.46 for the 1.22 and 0 61 mmol CuO/CeO2 samples respectively.Temperature-programmed reduction (TPR) profile with two reduction peaks at 156 and 16513 suggests that the reduction of highly dispersed Cu2+ ions consists of two steps and is easier than that of CuO crystallites,in which the TPR profile has only one reduction peak at about 249℃.The above experimental results are in good agreement with the prediction of the incorporation model.
基金Welch Foundation(#T-0014)and the CNMS user program of the Oak Ridge National LaboratoryAcknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research,ACS PRF(#57596-UR5).
文摘Five hundred ppm Pd/CeO2 catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction.Pd/CeO2 catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction.Excellent ethylene selectivity of〜100%was obtained in the whole reaction temperature range of 50℃-200℃ for samples calcined at temperatures of 600℃ and 800℃.This could be ascribed to the formation of PdX-Ce1-xO2-y or Pd-O-Ce surface species based on the X-ray diffiaction and X-ray photoelectron spectroscopy results,indicating the strong interaction between palladium and ceria.
基金supported financially by Shanghai Sailing Program(17YF1413100)Shanghai Rising-Star Program(19QB1401700).
文摘In the last decades,many reports dealing with technology for the catalytic combustion of methane(CH4)have been published.Recently,attention has increasingly focused on the synthesis and catalytic activity of nickel oxides.In this paper,a NiO/CeO2 catalyst with high catalytic performance in methane combustion was synthe-sized via a facile impregnation method,and its catalytic activity,stability,and water-resistance during CH4 com-bustion were investigated.X-ray diffraction,low-tempera-ture N2 adsorption,thermogravimetric analysis,Fourier transform infrared spectroscopy,hydrogen temperature programmed reduction,methane temperature programmed surface reaction,Raman spectroscopy,electron paramag-netic resonance,and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail.The incorporation of NiO was found to enhance the concentration of oxygen vacancies,as well as the activity and amount of surface oxygen.As a result,the mobility of bulk oxygen in CeO2 was increased.The presence of CeO2 prevented the aggregation of NiO,enhanced reduction by NiO,and provided more oxygen species for the combustion ofCH4.The results of a kinetics study indicated that the reaction order was about 1.07 for CH4 and about 0.10 for O2 over the NiO/CeO2 catalyst.
基金the National Natural Science Foundation of China (Nos.21673215 and 21473169)the Fundamental Research Funds for the Central Universities (No.WK2060030029)the Max-Planck Partner Group,Hefei Science Center,CAS,Users with Potential. The authors also gratefully thank the BL10B beamlines at National Synchrotron Radiation Laboratory (NSRL),China.
文摘Single-atom catalysts (SACs) have recently attracted broad attention in the catalysis field due to their maximized atom efficiency and unique catalytic properties.An atomic-level understanding of the interaction between the metal atoms and support is vital for developing stable and high-performance SACs.In this work,Pt1 single atoms with Ioadings up to 4 wt.% were fabricated on ceria nanorods using the atomic layer deposition technique.To understand the Pt-O-Ce bond interfacial interactions,the stability of Pt1 single atoms in the hydrogen reducing environment was extensively investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy CO chemisorption measurements.It was found that ceria defect sites,metal Ioadings and high-temperature calcination are effective ways to tune the stability of Pt1 single atoms in the hydrogen environment.X-ray photoemission spectroscopy further showed that Pt1 single atoms on ceria are dominantly at a +2 valence state at the defect and step edge sites,while those on terrace sites are at a +4 state.The above tailored stability and electronic properties of Pt1 single atoms are found to be strongly correlated with the catalytic activity in the dry and water-mediated CO oxidation reactions.
