Direct Measurement of Interaction Energy between Solids and Gases. II. Microcalorimetric Studies on the Surface Acidity and Acid Strength Distribution of Solid Acid Catalysts

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Abstract
The differential heats of adsorption of ammonia on several solid acids were measured by means of a twin conduction type microcalorimeter, and surface acid strength distribution and acidity were evaluated. Silica–alumina showed very high initial heats which were not observed in decationated zeolite and silica–magnesia. The acidity of zeolite was about 6 times as high as that of silica–alumina, showing very charactristic acid site distribution at 100 kJ/mol of adsorption energy, and suggesting the existence of homogeneous acid sites. The surface water modified surface acidic nature transforming strong acid sites into weaker ones. The poisoning of acid sites of silica-alumina with alkali occurred preferentially at sites on which adsorption energy of ammonia was 96–105kJ/mol.