Aluminium-to-silicon ratio on the surface of zeolites dealuminated using silicon tetrachloride vapour and acid leaching

Abstract

It was determined using X-ray photoelectron spectroscopy that Y zeolites, dealuminated with SiCl 4 and exhibiting an Al Si ratio from 0.30 to 0.05, have an aluminium-rich surface. After dehydration at 790 K and subsequent readsorption of water at ambient temperature, the amount of Al in the surface of dealuminated Y zeolites slightly decreases, outer layers remaining still enriched in Al, while with the non-modified zeolite NH 4Y this treatment results in appreciable Al deficiency of the surface. The acid leaching of NH 4Y and NaM zeolites, using HCl solutions with pH ranging from 4 to 1, tends to remove more Al atoms from the surface than from the bulk. Under these conditions, the amorphization of NH 4Y takes place.