Direct Measurement of Interaction Energy between Solids and Gases. I. Heat of Adsorption of Ammonia on Zeolite

Abstract

Abstract The differential heat of adsorption of ammonia on synthetic zeolites was calorimetrically measured and the distribution of the surface acidity was discussed in relation to the catalytic activity for cumene-cracking as a function of zeolite compositions. A newly designed apparatus, a twin-conduction-type calorimeter equipped with a semiconductor thermoelement and an adsorption apparatus, was used for the direct measurement of the differential heat of adsorption. The differential heat of adsorption of ammonia decreased with the increase in surface coverage, the acid site on the surface becoming stronger up to 27 kcal/mol for ammonia-adsorption when the ratio of silica to alumina was higher and the content of exchanged ammonium ions was higher. The cumene-cracking reaction was effectively catalyzed by zeolites having such sites with heat of adsorption of ammonia exceeding 25 kcal/mol.