Cu-based catalysts are commonly used in industry for methanol synthesis.In this study,supported catalysts of 5 wt%Cu/Al_(2)O_(3)and 5 wt%Cu/ZnO were prepared,and their surface characteristics during H_(2) reduction an...Cu-based catalysts are commonly used in industry for methanol synthesis.In this study,supported catalysts of 5 wt%Cu/Al_(2)O_(3)and 5 wt%Cu/ZnO were prepared,and their surface characteristics during H_(2) reduction and CO_(2)hydrogenation were investigated using in situ Fourier transform infrared spectroscopy(FTIR),ex situ X-ray photoelectron spectroscopy,and high sensitivity low energy ion scattering spectroscopy.During the H2 reduction and CO_(2)hydrogenation processes,it was found that Al_(2)O_(3)can stabilize Cu^(+).In situ FTIR spectra indicated that the 5 wt%Cu/Al_(2)O_(3)can adsorb large amounts of bicarbonate and carbonate species,which then convert into formate during CO_(2)hydrogenation.For the 5 wt%Cu/ZnO,it was found that Cu nanoparticles were gradually covered by a highly defective ZnOx overlayer during H2 reduction,which can effectively dissociate H2.During CO_(2)hydrogenation,the adsorbed bicarbonate or carbonate species can convert into formate and then into a methoxy species.Using these surface sensitive methods,a more in-depth understanding of the synergistic effect among the Cu,Al_(2)O_(3),and ZnO components of Cu-based catalysts was achieved.展开更多
Infrared(IR)absorption spectroscopy has been widely used for dynamic characterization of catalysts and mechanism of catalytic reactions.However,due to the strong infrared absorption of heterogeneous catalysts(mainly o...Infrared(IR)absorption spectroscopy has been widely used for dynamic characterization of catalysts and mechanism of catalytic reactions.However,due to the strong infrared absorption of heterogeneous catalysts(mainly oxides,or supported metal and metal oxides,etc.)below 1200 cm^(-1),and the intensity of regular infrared light source rapidly decays at low-wavenumber range,most in-situ infrared spectroscopy studies are limited to the detection of surface adsorbates in the range of 4000-900 cm^(-1).The change of catalytically active component itself(M-O,M-M bond,etc.,1200-50 cm^(-1))during the reaction is hard to be tracked under reaction conditions by in-situ IR.In this work,a home-made in-situ IR reactor was designed and a sample preparing method was developed.With such progresses,the changes of reactants,products,surface adsorbates,and catalysts themselves can be measured under the same reaction conditions with a spectral range of 4000-400 cm^(-1),providing a new opportunity for in-situ characterization of heterogeneous catalysis.CO oxidation on Pd/SiO_(2) and Cu/SiO_(2) catalysts were taken as examples,since both the two catalytic systems were extensively used commercially,and moreover reduction and oxidation of palladium and copper occur during the examined reaction conditions.The characteristic bands of Pd^(2+)-O(670,608 cm^(-1)),Cu^(+)-O(635 cm^(-1))and Cu^(2+)-O(595,535 cm^(-1))were observed by IR,and the changes during CO oxidation reaction were successfully monitored by IR.The oxidation/reduction of palladium and copper were also confirmed by ex-situ XPS.Moreover,Pd^(0) in Pd/SiO_(2) and Cu^(+)in Cu/SiO_(2) were found as the thermal dynamically stable phases under the examined conditions for CO oxidation.展开更多
We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high val...We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e, 3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of pi(M-O)* is involved in H abstraction by M = O, resulting in a (4e, 4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O pbond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.展开更多
Partial oxidation of methane to syngas （POM） over Rh/SiO2 catalyst was investigated using in-situ FT-IR. When methane interacted with 1.0wt%Rh/SiO2 catalyst, it was dissociated to adsorbed hydrogen and CHx species. ...Partial oxidation of methane to syngas （POM） over Rh/SiO2 catalyst was investigated using in-situ FT-IR. When methane interacted with 1.0wt%Rh/SiO2 catalyst, it was dissociated to adsorbed hydrogen and CHx species. The adsorbed hydrogen atoms were transferred to SiO2 surface by ＂spill-over＂ and reacted with lattice oxygen to form surface -OH species. POM mechanism was investigated over Rh/SiO2 catalyst using in-situ FT-IR. It was found that CO2 was formed before CO could be detected when CH4 and O2 were introduced over the preoxidized Rh/SiO2 catalyst, whereas CO was detected before CO2 was formed over the prereduced Rh/SiO2 catalyst.展开更多
A detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene convers...A detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene conversion and acrolein selectivity increased with the addition of MoO3 to TeMo5O16. Based on the results of N2 adsorption-desorption, XRD, XPS, in-situ XRD, O2-TPO, and 2-propanol decomposition reaction, the higher catalytic performance and synergetic effect could be attributed to the enhancement of acidity and the oxygen transfer from TeMo5O16 to MoO3 phase.展开更多
CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programined reaction. The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones. Model studie...CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programined reaction. The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones. Model studies were performed to better understand the oxidation state, reactivities and stabilities of partially oxidized Pd surfaces under CO oxidation reaction condi tions using an in situ infrared reflection absorption spectrometer （IRAS）. Three O/Pd（100） model surfaces, chemisorbed oxygen covered surface, surface oxide and bulk-like surface oxide, were prepared and characterized by low-energy electron diffraction （LEED） and Auger electron spectroscopy （AES）. The present work demonstrates that the oxidized palladium surface is less active for CO oxidation than the metallic surface, and is unstable under the reaction conditions with sufficient CO.展开更多
Cu-based catalyst has been widely used for catalytic reduction of NO.Well-defined TiO_(x)/Cu(110)films were prepared and investi-gated by in situ reflection absorption infrared spectroscopy(IRAS),Auger electron spectr...Cu-based catalyst has been widely used for catalytic reduction of NO.Well-defined TiO_(x)/Cu(110)films were prepared and investi-gated by in situ reflection absorption infrared spectroscopy(IRAS),Auger electron spectroscopy(AES)and low energy electron dif-fraction(LEED).A complex surface structure of Cu^(+)(-O-Ti-)-O-Cu^(δ+)/Cu(110)was proposed,in which the topmost surface Cu+is highly dispersed,isolated and fixed by the TiO_(x) layer.Such a'single atom'-like surface site appears a very narrow vco peak at 2130 cm^(-1),and is more stable upon both CO reduction and vacuum annealing than the Cu_(2)O/Cu(110).Such isolated Cu^(+)(-O-Ti-)site on TiO_(x)/Cu(110)is also fairly stable in NO+CO reaction,but the overall catalytic activity is slightly lower than that on the Cu(110)surface,indicating that the single-atom Cu^(+)(-O-Ti-)site is less efficient for NO+CO reaction at the examined conditions.The study provides useful infor-mation for the design and application of single-atom catalysts and understanding the nature of catalytically active centers.展开更多
Prof. Khi-Rui Tsai was born in Tongan （Xiamen, Fujian）, in the December of 1913. After graduted from Xiamen University in 1937, he was appointed as an assistant professor of Xiamen University. He was selected as a g...Prof. Khi-Rui Tsai was born in Tongan （Xiamen, Fujian）, in the December of 1913. After graduted from Xiamen University in 1937, he was appointed as an assistant professor of Xiamen University. He was selected as a government-supported oversea student to continue his educa- tion in the US in 1947, and obtained his PhD degree in 1950 from the Ohio State University.展开更多
Spin-polarized density functional theory （DPT） calculations are carried out to determine the site preference of H adsorption on Pd（100） surface and subsurface, We carefully scrutinize the energy difference between...Spin-polarized density functional theory （DPT） calculations are carried out to determine the site preference of H adsorption on Pd（100） surface and subsurface, We carefully scrutinize the energy difference between different patterns at θ=0.50 ML and confirm the LEED observation that surface adsorption can form c（2×2） ordering structure. On the contrary, we disclose that p（2×1） structure become more favorable than c（2×2） for subsurface adsorption. These site preferences are rationalized via an analysis of the layer and orbital resolved density of states. Furthermore, we propose that the interstitial charge as a key factor determining the preferred H adsorbed site.展开更多
The pure phase of praseodymium orthovanadate (PrVO\-4) has been prepared by the citrate method. The active site of PrVO\-4 was studied by ESR, NO_TPD, O\-2_TPD and 18 O\-2_isotope exchange methods. The results of ESR ...The pure phase of praseodymium orthovanadate (PrVO\-4) has been prepared by the citrate method. The active site of PrVO\-4 was studied by ESR, NO_TPD, O\-2_TPD and 18 O\-2_isotope exchange methods. The results of ESR and NO_TPD confirmed the presence of V 4+ in the catalyst. 18 O\-2_isotope exchange was through a single exchange procedure. From the result of O\-2+TPD and the kinetic study of 18 O\-2_isotope exchange, one can reach a conclusion that the V 4+ species associated with oxygen vacancies are the site for O\-2 activation. The adsorbed O\-2 or O\+- are the active oxygen species in propane oxidative dehydrogenation.展开更多
文摘Cu-based catalysts are commonly used in industry for methanol synthesis.In this study,supported catalysts of 5 wt%Cu/Al_(2)O_(3)and 5 wt%Cu/ZnO were prepared,and their surface characteristics during H_(2) reduction and CO_(2)hydrogenation were investigated using in situ Fourier transform infrared spectroscopy(FTIR),ex situ X-ray photoelectron spectroscopy,and high sensitivity low energy ion scattering spectroscopy.During the H2 reduction and CO_(2)hydrogenation processes,it was found that Al_(2)O_(3)can stabilize Cu^(+).In situ FTIR spectra indicated that the 5 wt%Cu/Al_(2)O_(3)can adsorb large amounts of bicarbonate and carbonate species,which then convert into formate during CO_(2)hydrogenation.For the 5 wt%Cu/ZnO,it was found that Cu nanoparticles were gradually covered by a highly defective ZnOx overlayer during H2 reduction,which can effectively dissociate H2.During CO_(2)hydrogenation,the adsorbed bicarbonate or carbonate species can convert into formate and then into a methoxy species.Using these surface sensitive methods,a more in-depth understanding of the synergistic effect among the Cu,Al_(2)O_(3),and ZnO components of Cu-based catalysts was achieved.
文摘Infrared(IR)absorption spectroscopy has been widely used for dynamic characterization of catalysts and mechanism of catalytic reactions.However,due to the strong infrared absorption of heterogeneous catalysts(mainly oxides,or supported metal and metal oxides,etc.)below 1200 cm^(-1),and the intensity of regular infrared light source rapidly decays at low-wavenumber range,most in-situ infrared spectroscopy studies are limited to the detection of surface adsorbates in the range of 4000-900 cm^(-1).The change of catalytically active component itself(M-O,M-M bond,etc.,1200-50 cm^(-1))during the reaction is hard to be tracked under reaction conditions by in-situ IR.In this work,a home-made in-situ IR reactor was designed and a sample preparing method was developed.With such progresses,the changes of reactants,products,surface adsorbates,and catalysts themselves can be measured under the same reaction conditions with a spectral range of 4000-400 cm^(-1),providing a new opportunity for in-situ characterization of heterogeneous catalysis.CO oxidation on Pd/SiO_(2) and Cu/SiO_(2) catalysts were taken as examples,since both the two catalytic systems were extensively used commercially,and moreover reduction and oxidation of palladium and copper occur during the examined reaction conditions.The characteristic bands of Pd^(2+)-O(670,608 cm^(-1)),Cu^(+)-O(635 cm^(-1))and Cu^(2+)-O(595,535 cm^(-1))were observed by IR,and the changes during CO oxidation reaction were successfully monitored by IR.The oxidation/reduction of palladium and copper were also confirmed by ex-situ XPS.Moreover,Pd^(0) in Pd/SiO_(2) and Cu^(+)in Cu/SiO_(2) were found as the thermal dynamically stable phases under the examined conditions for CO oxidation.
基金financial support from the National Nature Science Foundation of China (21133004,21373167,21573178)the Fundamental Research Funds for the Central Universities (20720160046)the Program for Innovative Research Team in Chinese Universities (IRT_14R31)
文摘We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e, 3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of pi(M-O)* is involved in H abstraction by M = O, resulting in a (4e, 4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O pbond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.
基金This study was supported by the grant of 2004C31053 from the Ministry of Science and Technology of Zhejiang Province, China, and the grant of Y404305 from the Natural Science Foundation of Zhejiang Province, Chinathe grant of 20673101, 20673102 from National Natural Science Foundation of China.
文摘Partial oxidation of methane to syngas （POM） over Rh/SiO2 catalyst was investigated using in-situ FT-IR. When methane interacted with 1.0wt%Rh/SiO2 catalyst, it was dissociated to adsorbed hydrogen and CHx species. The adsorbed hydrogen atoms were transferred to SiO2 surface by ＂spill-over＂ and reacted with lattice oxygen to form surface -OH species. POM mechanism was investigated over Rh/SiO2 catalyst using in-situ FT-IR. It was found that CO2 was formed before CO could be detected when CH4 and O2 were introduced over the preoxidized Rh/SiO2 catalyst, whereas CO was detected before CO2 was formed over the prereduced Rh/SiO2 catalyst.
基金supported by the grants from the Research Initiation Funds for the Doctor of Zhejiang Normal University (ZC304008169)the National Natural Science Foundation of China (21003108)
文摘A detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene conversion and acrolein selectivity increased with the addition of MoO3 to TeMo5O16. Based on the results of N2 adsorption-desorption, XRD, XPS, in-situ XRD, O2-TPO, and 2-propanol decomposition reaction, the higher catalytic performance and synergetic effect could be attributed to the enhancement of acidity and the oxygen transfer from TeMo5O16 to MoO3 phase.
基金supported by the National Basic Research Program of China(2010CB732303,2013CB933102)the Major Project of Chinese Ministry of Education(309019)+2 种基金the National Natural Science Foundation of China(21033006,21073149,21273178)the Program for Changjiang Scholars and Innovative Research Team in University(IRT1036)the Ph.D Programs foundation of Chinese Ministry of Education(20110121110010)
文摘CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programined reaction. The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones. Model studies were performed to better understand the oxidation state, reactivities and stabilities of partially oxidized Pd surfaces under CO oxidation reaction condi tions using an in situ infrared reflection absorption spectrometer （IRAS）. Three O/Pd（100） model surfaces, chemisorbed oxygen covered surface, surface oxide and bulk-like surface oxide, were prepared and characterized by low-energy electron diffraction （LEED） and Auger electron spectroscopy （AES）. The present work demonstrates that the oxidized palladium surface is less active for CO oxidation than the metallic surface, and is unstable under the reaction conditions with sufficient CO.
基金This work was supported by the National Natural Science Foundation of China(21872110,21327901)the National Key Research and Development Program of China(2020YFB0606401).
文摘Cu-based catalyst has been widely used for catalytic reduction of NO.Well-defined TiO_(x)/Cu(110)films were prepared and investi-gated by in situ reflection absorption infrared spectroscopy(IRAS),Auger electron spectroscopy(AES)and low energy electron dif-fraction(LEED).A complex surface structure of Cu^(+)(-O-Ti-)-O-Cu^(δ+)/Cu(110)was proposed,in which the topmost surface Cu+is highly dispersed,isolated and fixed by the TiO_(x) layer.Such a'single atom'-like surface site appears a very narrow vco peak at 2130 cm^(-1),and is more stable upon both CO reduction and vacuum annealing than the Cu_(2)O/Cu(110).Such isolated Cu^(+)(-O-Ti-)site on TiO_(x)/Cu(110)is also fairly stable in NO+CO reaction,but the overall catalytic activity is slightly lower than that on the Cu(110)surface,indicating that the single-atom Cu^(+)(-O-Ti-)site is less efficient for NO+CO reaction at the examined conditions.The study provides useful infor-mation for the design and application of single-atom catalysts and understanding the nature of catalytically active centers.
文摘Prof. Khi-Rui Tsai was born in Tongan （Xiamen, Fujian）, in the December of 1913. After graduted from Xiamen University in 1937, he was appointed as an assistant professor of Xiamen University. He was selected as a government-supported oversea student to continue his educa- tion in the US in 1947, and obtained his PhD degree in 1950 from the Ohio State University.
基金supported by the National Nature Science Foundation of China(21131005,20925103,21373167,21033006,21133004,21333008)the Fundamental Research Funds of Central Universities
文摘Spin-polarized density functional theory （DPT） calculations are carried out to determine the site preference of H adsorption on Pd（100） surface and subsurface, We carefully scrutinize the energy difference between different patterns at θ=0.50 ML and confirm the LEED observation that surface adsorption can form c（2×2） ordering structure. On the contrary, we disclose that p（2×1） structure become more favorable than c（2×2） for subsurface adsorption. These site preferences are rationalized via an analysis of the layer and orbital resolved density of states. Furthermore, we propose that the interstitial charge as a key factor determining the preferred H adsorbed site.
文摘The pure phase of praseodymium orthovanadate (PrVO\-4) has been prepared by the citrate method. The active site of PrVO\-4 was studied by ESR, NO_TPD, O\-2_TPD and 18 O\-2_isotope exchange methods. The results of ESR and NO_TPD confirmed the presence of V 4+ in the catalyst. 18 O\-2_isotope exchange was through a single exchange procedure. From the result of O\-2+TPD and the kinetic study of 18 O\-2_isotope exchange, one can reach a conclusion that the V 4+ species associated with oxygen vacancies are the site for O\-2 activation. The adsorbed O\-2 or O\+- are the active oxygen species in propane oxidative dehydrogenation.
