{"title":"氧化负载烯烃转化催化剂的x射线吸收光谱表征","authors":"J. Evans, J. Gauntlett, J. Mosselmans","doi":"10.1039/DC9908900107","DOIUrl":null,"url":null,"abstract":"An X-ray absorption spectroscopy (XAS) cell has been developed to allow the loading of air-sensitive catalyst precursors in a glove box and their in situ activation and operation to be monitored. This has been used to investigate two alumina-supported propene metathesis catalysts derived from Mo2(OAc)4 and Li4[Mo2Me8]. The EXAFS data so derived has been analysed by spherical wave methods using ab initio phase shifts and back-scattering factors. The detailed structural features obtained are sample-history dependent, but the following general observations can be drawn about the mean surface species present. In all cases the quadruple Mo—Mo bond is cleaved on the surface; some samples show evidence of one (or fewer) metal atoms at longer distances. For the latter sample activation in vacuo at 70°C yielded sites approximating to [MoO2(Me)2(O-)]n. The addition of propene caused a change in the XAS spectra. There was evidence of a shell with MoC distance of ca 1.8 A that can be attributed to a terminal carbene ligand. For one of the Mo2(OAc)4-derived catalysts there was also evidence for a molybdacyclobutane unit. The Li4[Mo2Me8]-based materials also showed evidence of residual MoO bonds after exposure to propene. The Zr K-edge EXAFS of Zr(allyl)4/oxide (oxide = silica and alumina) were very similar for a range of sample conditions, showing evidence for a residual allyl group and Zr-O bonds.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"39 1","pages":"107-117"},"PeriodicalIF":0.0000,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"10","resultStr":"{\"title\":\"Characterisation of oxide-supported alkene conversion catalysts using X-ray absorption spectroscopy\",\"authors\":\"J. Evans, J. Gauntlett, J. Mosselmans\",\"doi\":\"10.1039/DC9908900107\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"An X-ray absorption spectroscopy (XAS) cell has been developed to allow the loading of air-sensitive catalyst precursors in a glove box and their in situ activation and operation to be monitored. This has been used to investigate two alumina-supported propene metathesis catalysts derived from Mo2(OAc)4 and Li4[Mo2Me8]. The EXAFS data so derived has been analysed by spherical wave methods using ab initio phase shifts and back-scattering factors. The detailed structural features obtained are sample-history dependent, but the following general observations can be drawn about the mean surface species present. In all cases the quadruple Mo—Mo bond is cleaved on the surface; some samples show evidence of one (or fewer) metal atoms at longer distances. For the latter sample activation in vacuo at 70°C yielded sites approximating to [MoO2(Me)2(O-)]n. The addition of propene caused a change in the XAS spectra. There was evidence of a shell with MoC distance of ca 1.8 A that can be attributed to a terminal carbene ligand. For one of the Mo2(OAc)4-derived catalysts there was also evidence for a molybdacyclobutane unit. The Li4[Mo2Me8]-based materials also showed evidence of residual MoO bonds after exposure to propene. The Zr K-edge EXAFS of Zr(allyl)4/oxide (oxide = silica and alumina) were very similar for a range of sample conditions, showing evidence for a residual allyl group and Zr-O bonds.\",\"PeriodicalId\":12210,\"journal\":{\"name\":\"Faraday Discussions of The Chemical Society\",\"volume\":\"39 1\",\"pages\":\"107-117\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"1990-01-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"10\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Faraday Discussions of The Chemical Society\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.1039/DC9908900107\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Faraday Discussions of The Chemical Society","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1039/DC9908900107","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Characterisation of oxide-supported alkene conversion catalysts using X-ray absorption spectroscopy
An X-ray absorption spectroscopy (XAS) cell has been developed to allow the loading of air-sensitive catalyst precursors in a glove box and their in situ activation and operation to be monitored. This has been used to investigate two alumina-supported propene metathesis catalysts derived from Mo2(OAc)4 and Li4[Mo2Me8]. The EXAFS data so derived has been analysed by spherical wave methods using ab initio phase shifts and back-scattering factors. The detailed structural features obtained are sample-history dependent, but the following general observations can be drawn about the mean surface species present. In all cases the quadruple Mo—Mo bond is cleaved on the surface; some samples show evidence of one (or fewer) metal atoms at longer distances. For the latter sample activation in vacuo at 70°C yielded sites approximating to [MoO2(Me)2(O-)]n. The addition of propene caused a change in the XAS spectra. There was evidence of a shell with MoC distance of ca 1.8 A that can be attributed to a terminal carbene ligand. For one of the Mo2(OAc)4-derived catalysts there was also evidence for a molybdacyclobutane unit. The Li4[Mo2Me8]-based materials also showed evidence of residual MoO bonds after exposure to propene. The Zr K-edge EXAFS of Zr(allyl)4/oxide (oxide = silica and alumina) were very similar for a range of sample conditions, showing evidence for a residual allyl group and Zr-O bonds.