E. Dooryhee, G. Greaves, A. T. Steel, R. P. Townsend, S. Carr, John Meurig Thomas, C. Catlow
{"title":"高分辨率x射线粉末衍射和x射线吸收光谱相结合的高面积沸石吸附剂和催化剂的结构研究","authors":"E. Dooryhee, G. Greaves, A. T. Steel, R. P. Townsend, S. Carr, John Meurig Thomas, C. Catlow","doi":"10.1039/DC9908900119","DOIUrl":null,"url":null,"abstract":"We have characterized at high temperature a model uniform heterogeneous catalyst for the oligomerization of hydrocarbons (a nickel-exchanged zeolite of initial composition Na59Al59Si133O384·xH2O treated with an aqueous solution of NiCl2 so as to yield a homogeneous distribution of Ni, with Si/Ni = 7) by recording the extended X-ray absorption fine structure (EXAFS) above the Ni edge and also its high-resolution diffraction pattern (at λ= 1.5486 A). We have obtained unique insights into the microenvironment of the Ni2+ ions in the as-prepared and the dehydrated as well as the reduced state of the catalyst; in particular, values of atomic coordinates, site-occupancy and bond lengths, have been obtained. High-resolution X-ray diffraction, using a specially constructed environmental cell, has enabled the precise location of sorbed Xe atoms in a sodium-exchanged zeolite X adsorbent (1.5 atoms of Xe per unit cell) under a pressure of 1.75 bar at room temperature to be determined from a Rietveld refinement of the powder diffraction pattern. Direct proof of the role of the strongly polarizing Na+ ion located at the SΠ site in firmly binding the Xe to the inner wall of the supercage is obtained.X-ray absorption near-edge structures (XANES) as well as parallel EXAFS studies above the Al, Si and Ga edges on a variety of other zeolites are also reported. Combined (Ga edge) XANES and EXAFS studies show that gallosilicate networks akin to those present in crystalline (gallo) zeolite X and Y are already formed in the precursor gel and are also present in the aqueous solution in contact with the colloidal-amorphous material, which together constitute the gel. We also report one of the first applications of Al EXAFS for the semi-quantitative study of the dealumination of faujasitic zeolites.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"246 1","pages":"119-136"},"PeriodicalIF":0.0000,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"47","resultStr":"{\"title\":\"Structural studies of high-area zeolitic adsorbents and catalysts by a combination of high-resolution X-ray powder diffraction and X-ray absorption spectroscopy\",\"authors\":\"E. Dooryhee, G. Greaves, A. T. Steel, R. P. Townsend, S. Carr, John Meurig Thomas, C. Catlow\",\"doi\":\"10.1039/DC9908900119\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"We have characterized at high temperature a model uniform heterogeneous catalyst for the oligomerization of hydrocarbons (a nickel-exchanged zeolite of initial composition Na59Al59Si133O384·xH2O treated with an aqueous solution of NiCl2 so as to yield a homogeneous distribution of Ni, with Si/Ni = 7) by recording the extended X-ray absorption fine structure (EXAFS) above the Ni edge and also its high-resolution diffraction pattern (at λ= 1.5486 A). We have obtained unique insights into the microenvironment of the Ni2+ ions in the as-prepared and the dehydrated as well as the reduced state of the catalyst; in particular, values of atomic coordinates, site-occupancy and bond lengths, have been obtained. High-resolution X-ray diffraction, using a specially constructed environmental cell, has enabled the precise location of sorbed Xe atoms in a sodium-exchanged zeolite X adsorbent (1.5 atoms of Xe per unit cell) under a pressure of 1.75 bar at room temperature to be determined from a Rietveld refinement of the powder diffraction pattern. Direct proof of the role of the strongly polarizing Na+ ion located at the SΠ site in firmly binding the Xe to the inner wall of the supercage is obtained.X-ray absorption near-edge structures (XANES) as well as parallel EXAFS studies above the Al, Si and Ga edges on a variety of other zeolites are also reported. Combined (Ga edge) XANES and EXAFS studies show that gallosilicate networks akin to those present in crystalline (gallo) zeolite X and Y are already formed in the precursor gel and are also present in the aqueous solution in contact with the colloidal-amorphous material, which together constitute the gel. We also report one of the first applications of Al EXAFS for the semi-quantitative study of the dealumination of faujasitic zeolites.\",\"PeriodicalId\":12210,\"journal\":{\"name\":\"Faraday Discussions of The Chemical Society\",\"volume\":\"246 1\",\"pages\":\"119-136\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"1990-01-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"47\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Faraday Discussions of The Chemical Society\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.1039/DC9908900119\",\"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/DC9908900119","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Structural studies of high-area zeolitic adsorbents and catalysts by a combination of high-resolution X-ray powder diffraction and X-ray absorption spectroscopy
We have characterized at high temperature a model uniform heterogeneous catalyst for the oligomerization of hydrocarbons (a nickel-exchanged zeolite of initial composition Na59Al59Si133O384·xH2O treated with an aqueous solution of NiCl2 so as to yield a homogeneous distribution of Ni, with Si/Ni = 7) by recording the extended X-ray absorption fine structure (EXAFS) above the Ni edge and also its high-resolution diffraction pattern (at λ= 1.5486 A). We have obtained unique insights into the microenvironment of the Ni2+ ions in the as-prepared and the dehydrated as well as the reduced state of the catalyst; in particular, values of atomic coordinates, site-occupancy and bond lengths, have been obtained. High-resolution X-ray diffraction, using a specially constructed environmental cell, has enabled the precise location of sorbed Xe atoms in a sodium-exchanged zeolite X adsorbent (1.5 atoms of Xe per unit cell) under a pressure of 1.75 bar at room temperature to be determined from a Rietveld refinement of the powder diffraction pattern. Direct proof of the role of the strongly polarizing Na+ ion located at the SΠ site in firmly binding the Xe to the inner wall of the supercage is obtained.X-ray absorption near-edge structures (XANES) as well as parallel EXAFS studies above the Al, Si and Ga edges on a variety of other zeolites are also reported. Combined (Ga edge) XANES and EXAFS studies show that gallosilicate networks akin to those present in crystalline (gallo) zeolite X and Y are already formed in the precursor gel and are also present in the aqueous solution in contact with the colloidal-amorphous material, which together constitute the gel. We also report one of the first applications of Al EXAFS for the semi-quantitative study of the dealumination of faujasitic zeolites.