ISOTHERMS OF CHEMICAL ADSORPTION OF BASES ON SOLID CATALYSTS FOR ACIDITY MEASUREMENT

The measurement of the adsorption equilibrium constants of the bases a nd the total mass of base adsorbed at 200-degrees-C are proposed as re producible indices of average acidity strength and of total acidity of the solid, respectively. The adsorption of different bases (ammonia, n-butylamine, tert-butylamine, pyridine) in gas phase on solid acidic catalysts (silica-lumina and zeolite catalysts and a silica gel) has b een studied, by applying the calorimetric method in flow regime throug h an isothermal bed of solid. Both the conditions under which the adso rption is exclusively chemical as well as those under which the adsorp tion is not limited by the internal diffusion of the base have been de termined. For these acidity measurements tert-butylamine behaves well and is an alternative base to ammonia.