Interaction of zeolite alumina with matrix silica in catalytic cracking catalysts

A set of steamed ultra-stable (US) Y and acid-treated, aluminium deficient (AD) USY zeolites have been prepared. The removal of zeolite non-framework aluminium (EFAL) oxides from USY increases the micro- and meso-pore areas and the numbers of Brønsted and Lewis acid sites. However, when both USY and ADUSY are steamed, they have equivalent numbers of acid sites in spite of a larger difference in EFAL oxide content. Zeolites USY and ADUSY have also been mixed intimately with silica and steamed. Evidence is presented using27Al magic angle spinning (MAS) NMR spectroscopy and the IR pyridine adsorption technique, which indicates that EFAL oxides depolymerise during the steam treatment in the presence of silica to produce a silica—alumina phase.