Comparison of the information given by ammonia t.p.d. and pyridine adsorption—desorption on the acidity of dealuminated HY and LaHY zeolite cracking catalysts

Two series of dealuminated Y zeolites with framework Si Al ratio in the 2.5–24 range have been prepared by two different methods, that is, deep bed calcination ad SiCl4 treatment. It is shown that a disordered unit cell model with a random distribution of aluminium in the framework can be applied in this range of Si Al ratio. The acidity distribution in these samples has been measured by t.p.d. of ammonia and i.r. of adsorbed pyridine, and the results are related with different types of specific acid sites. By ammonia t.p.d. up to 550°C, sites with zero and one aluminiums in the second coordination sphere can be jointly measured, but the separate contributions of these two centers can be achieved only by i.r. by adsorbed pyridine.