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Powder X-ray diffraction has been used to investigate the crystal structure of various dealuminated Y-type zeolites in order to study framework vacancies and non-framework species, in relation to the dealurnination process. The number of framework vacancies has been determined for different dealumination modes, degrees of dealumination and acid or basic treatments. Information has been provided on the nature of extraframework species. Their number and position have also been specified. It has been shown that for all investigated samples, these species are found in sodalite cages [sites S(1') and S(II')], and also in supercages [S(II)] for the least dealuminated sample. Aluminium and silicon framework populations have been calculated from X-ray diffraction combined with magic-angle spinning n.m.r. data so as to understand the dealumination mechanism.

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