Aluminium distribution in the bulk and on the surface of Y zeolites dealuminated with SiCl4 vapour. Influence of conditions of dealumination

Abstract

Zeolites Y, dealuminated by reaction with SiCl₄ at 530 and 630 K followed by washing with water, ethanol or ethanol and buffer before ammonium exchange (resulting Si/Al ratio: 3.8–10.6), have been examined using X-ray photoelectron spectroscopic measurements combined with chemical analysis. Subsequent extraction with H₂Na₂ EDTA allowed preferential removal of non-framework Al species which helped in the discussion of the Al location. It was found that, besides the increase of reaction temperature, the efficiency of washing (water > ethanol > ethanol and buffer) increases the Si/Al ratio both in the bulk and on the surface. Temperature increase and milder washing enhance the Al-enrichment of the surface with respect to the bulk. Non-framework Al species are responsible for the surface enrichment.