Adsorption of methanol in zeolite, gallosilicate and SAPO catalysts

Abstract

Methanol adsorption in zeolite, gallosilicate and silicoaluminophosphate (SAPO) catalysts has been investigated within the framework of ab initio molecular orbital calculations. Full optimization of all cluster models and their complexes has been carried out at the DZP/SCF level of theory. Physisorbed methanol and methoxonium cation complexed to the framework catalyst are found for SAPO catalysts, the latter complexes are observed only at high coverages, while only hydrogen-bonded physisorbed methanol complexes are obtained for gallosilicates and zeolitic catalysts. The conversion energy of the hydrogen-bonded physisorbed structure, H3SiOHAl(OH)2OPH3/[CH3OH]2to the methoxonium structure, H3SiOAl(OH)2OPH3]/[CH3OH2+][CH3OH], is about 6.69 kcal/mol. Comparison with hydrogen halides and related complexes of methanol shows that protonated SAPO/methanol is a very strong acid. © 1995.