UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vana-dium oxide catalysts.The real time reaction status of soot combustion over these catalysts was de-tected by in-situ UV-Ra...UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vana-dium oxide catalysts.The real time reaction status of soot combustion over these catalysts was de-tected by in-situ UV-Raman spectroscopy.The results indicate that TiO2 undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature.However,no obvious phase transformation process is observed for ZrO2 support.The structures of supported va-nadium oxides also depend on the V loading.The vanadium oxide species supported on TiO2 or ZrO2 attain monolayer saturation when V loading is equal to 4(4 is the number of V atoms per 100 support metal ions).Interestingly,this loading ratio(V4/TiO2 and V4/ZrO2) gave the best catalytic activities for soot combustion reaction on both supports(TiO2 and ZrO2).The formation of surface oxygen com-plexes(SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion.The presence of NO in the reaction gas stream can promote the pro-duction of SOC.展开更多
提出了应用高效NaY沸石导向剂快速合成A型沸石的新方法.在合成过程中,NaY沸石导向剂提供了全部硅源(无需另加硅源).与用水玻璃提供硅源的合成方法相比,该法晶化速度快,合成温度低,并可在低碱度条件下合成超细A型沸石.29S i NMR表征和UV ...提出了应用高效NaY沸石导向剂快速合成A型沸石的新方法.在合成过程中,NaY沸石导向剂提供了全部硅源(无需另加硅源).与用水玻璃提供硅源的合成方法相比,该法晶化速度快,合成温度低,并可在低碱度条件下合成超细A型沸石.29S i NMR表征和UV Ram an研究表明,高效NaY沸石导向剂中含有大量的六元环等低分子量硅铝酸根前驱体,它们有利于A型沸石成核与晶体生长.展开更多
Various VO_x/SiO_2 catalysts were prepared by the methods of physical mixing,conventional wetness impregnation and ultrasonication-assistant impregnation. The catalysts werecharacterized by XRD, UV-Vis DRS, Raman, TPR...Various VO_x/SiO_2 catalysts were prepared by the methods of physical mixing,conventional wetness impregnation and ultrasonication-assistant impregnation. The catalysts werecharacterized by XRD, UV-Vis DRS, Raman, TPR, ESR and TPSR techniques and the nature of the vanadiumspecies were correlated to their catalytic performance in the reaction of direct conversion ofmethane to formaldehyde. It is concluded that highly dispersed monomeric and low oligomeric vanadiaspecies are formed on the sample prepared with both traditional wetness impregnation method andultrasonication-assistant impregnation, whereas in the latter case, the amount of oligomeric vanadiaspecies is much smaller. The V_2O_5 microcrystallines are the dominant species on the materialprepared by physical mixing method. During the selective oxidation of methane, V^V species arereduced to V^(IV) paramagnetic species and both microcrystalline V_2O_5 species and oligomericvanadia species are found to further disperse and transform into tetrahedral vanadia species. Basedon the results of UV Raman spectroscopy and TPSR, CO_2 is suggested to be formed via two differentroutes, in which one is from the sequence reaction of CH_4 → HCHO → CO → CO_2 over monomericvanadia species, and the other is from the direct oxidation of methane to CO_2 over oligomericvanadia species. Oligomeric vanadia species is more active than monomeric vanadia species formethane activation.展开更多
基金the National Natural Science Foundation of China(Grant Nos.20473053,20773163 and 20525621)the Beijing Natural Science Foundation(Grant No.2062020)the 863 Program of China(Grant No.2006AA06Z346)
文摘UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vana-dium oxide catalysts.The real time reaction status of soot combustion over these catalysts was de-tected by in-situ UV-Raman spectroscopy.The results indicate that TiO2 undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature.However,no obvious phase transformation process is observed for ZrO2 support.The structures of supported va-nadium oxides also depend on the V loading.The vanadium oxide species supported on TiO2 or ZrO2 attain monolayer saturation when V loading is equal to 4(4 is the number of V atoms per 100 support metal ions).Interestingly,this loading ratio(V4/TiO2 and V4/ZrO2) gave the best catalytic activities for soot combustion reaction on both supports(TiO2 and ZrO2).The formation of surface oxygen com-plexes(SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion.The presence of NO in the reaction gas stream can promote the pro-duction of SOC.
基金The Programme Strategic Scientific Alliances between China and the Netherlands(2008DFB50130)National Basic Research Program of China (2009CB623503,2005CB221407)
文摘提出了应用高效NaY沸石导向剂快速合成A型沸石的新方法.在合成过程中,NaY沸石导向剂提供了全部硅源(无需另加硅源).与用水玻璃提供硅源的合成方法相比,该法晶化速度快,合成温度低,并可在低碱度条件下合成超细A型沸石.29S i NMR表征和UV Ram an研究表明,高效NaY沸石导向剂中含有大量的六元环等低分子量硅铝酸根前驱体,它们有利于A型沸石成核与晶体生长.
基金Financial support from the Ministry of Science and Technology of China(National Key Project of Fundamental Research:Grant G1999022406)is gratefully acknowledged.
文摘Various VO_x/SiO_2 catalysts were prepared by the methods of physical mixing,conventional wetness impregnation and ultrasonication-assistant impregnation. The catalysts werecharacterized by XRD, UV-Vis DRS, Raman, TPR, ESR and TPSR techniques and the nature of the vanadiumspecies were correlated to their catalytic performance in the reaction of direct conversion ofmethane to formaldehyde. It is concluded that highly dispersed monomeric and low oligomeric vanadiaspecies are formed on the sample prepared with both traditional wetness impregnation method andultrasonication-assistant impregnation, whereas in the latter case, the amount of oligomeric vanadiaspecies is much smaller. The V_2O_5 microcrystallines are the dominant species on the materialprepared by physical mixing method. During the selective oxidation of methane, V^V species arereduced to V^(IV) paramagnetic species and both microcrystalline V_2O_5 species and oligomericvanadia species are found to further disperse and transform into tetrahedral vanadia species. Basedon the results of UV Raman spectroscopy and TPSR, CO_2 is suggested to be formed via two differentroutes, in which one is from the sequence reaction of CH_4 → HCHO → CO → CO_2 over monomericvanadia species, and the other is from the direct oxidation of methane to CO_2 over oligomericvanadia species. Oligomeric vanadia species is more active than monomeric vanadia species formethane activation.
