COAPO MOLECULAR-SIEVE ACIDITY INVESTIGATED BY ADSORPTION CALORIMETRY AND IR SPECTROSCOPY

The acidic properties of cobalt- and silicon-substituted AlPO-5, -11 a nd -44 have been characterized by adsorption calorimetry and IR measur ements. Adsorption calorimetric measurements indicate that the adsorpt ion potential of the samples for acetonitrile is enhanced upon cobalt incorporation. The calorimetrically measured heats of adsorption indic ate the formation of strong acid sites, due to this cobalt incorporati on, as well as the presence of weaker acid sites, probably terminal P- OH groups. IR measurements of adsorbed ammonia and acetonitrile indica te that some Bronsted-bonded ammonia and acetonitrile are present, in combination with Lewis-bonded species. The Bronsted-bonded species pre sumably originate from interaction of the base with the weakly acidic P-OH groups. The Lewis-bonded species are due to the coordinative inte raction of the lone pair of the base with framework cobalt ions.