CoAPO molecular sieve acidity investigated by adsorption calorimetry and IR spectroscopy

Abstract

The acidic properties of cobalt-and silicon-substituted AlPO-5, –11 and –44 have been characterized by adsorption calorimetry and IR measurements. Adsorption calorimetric measurements indicate that the adsorption potential of the samples for acetonitrile is enhanced upon cobalt incorporation. The calorimetrically measured heats of adsorption indicate the formation of strong acid sites, due to this cobalt incorporation, as well as the presence of weaker acid sites, probably terminal P—OH groups. IR measurements of adsorbed ammonia and acetonitrile indicate that some Brønsted-bonded ammonia and acetonitrile are present, in combination with Lewis-bonded species. The Brønsted-bonded species presumably originate from interaction of the base with the weakly acidic P—OH groups. The Lewis-bonded species are due to the coordinative interaction of the lone pair of the base with framework cobalt ions.