CHARACTERIZATION OF ACIDITY IN ALPO4-AL2O3 (5-15-WT-PERCENT AL2O3) CATALYSTS USING PYRIDINE TEMPERATURE-PROGRAMMED DESORPTION

TPD of pyridine desorbed from the surface of AlPO4-Al2O3 catalysts, wi th different Al2O3 loadings (5-15 wt%), yields a complex desorption cu rve consisting of three overlapped peaks which are ascribable to weak (T-m approximate to 460 K), medium (T-m approximate to 530 K) and stro ng (T-m approximate to 590 K) acid sites (Bronsted and Lewis). There i s a homogeneous distribution of acid strength and an increase in alumi na loading leads to an increase in the number of pyridine-adsorbing si tes, even though there is no change in the strength distribution when catalysts are calcined at 773-1073 K. Furthermore, calcination at 1273 K reduces both the number and strength of the acid sites as the alumi na content increases. The overall number of acid sites decreases conti nuously as the temperature of the pyridine adsorption increases.