Direct measurement of the interaction energy between solids and gases. V. Change of the differential heats of adsorption of ammonia with specific poisoning on silica-alumina.

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Heats of adsorption of ammonia on specifically poisoned silica–alumina were measured by use of a twin-conduction-type calorimeter in order to elucidate the adsorption energy and acid strength distributions for both Brönsted (hereafter referred to as B) and Lewis (L) acid sites. Infrared spectra of adsorbed pyridine and cumene cracking activity for the poisoned sample were also examined. Sodium alcoholate–alcohol solution was used as the reagent poisoning only B sites. The use of sodium 2-propanolate–2-propanole dilute solution of which sodium contents was approximately equal to the expected amount of proton on silica–alumina surface caused a large portion of B sites to be poisoned without the decrease in the number of L sites. The following conclusions could be drawn from the experimental results that i) above 115 kJ/mol of the differential heat of adsorption of ammonia no B acid sites were present but only L acid sites, and ii) B acid sites existed chiefly in the vicinity of the adsorption energy distribution of 110 kJ/mol.
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