Induction of mesoporosity in ALPO-5. Treatment with silicon tetrachloride

Abstract

Reaction of microporous AlPO4 (ALPO-5) with SiCl4 vapour in a nitrogen atmosphere at 870 K results in the partial isomorphous substitution of P predominantly by Si. The product has fewer but stronger acid sites than the parent phase, whilst crystallinity is retained. Isothermal adsorption studies with H2O and N2 probe molecules indicates that some adsorption sites are lost via reaction with SiCl 4, and there is evidence for the development of mesoporosity in addition to the micropores already present. It is argued that reaction occurs preferentially at the intercrystallite regions in the aggregates, and at intracrystalline defects, i.e. defects in the pore structure. Comparisons with SAPO-5 are also made.