Influence of the Method of Dealumination of Y Zeolites on its Behaviour for Cracking N-Heptane and Vacuum Gas-Oil.

Y zeolites dealuminated by steam, SiCl4. and (NH4)2F6Si have been characterized by XPS, i.r., pyridine adsorption-desorption and nitrogen adsorption. Their catalytic activity for cracking n-heptane and vacuum gas-oil has been measured. Different behaviour of the samples for the two reactants has been observed. In all samples different types of extraframework aluminium (EFAL) species have been detected. A type of amorphous material related with EFAL, probably as amorphous silica-alumina, shows hydroxyl groups at 3600 cm~l with strong acidity and catalytic activity. In the case of n-heptane the framework Si/Al ratio and the amount of the active EFAL related with amorphous material plays a predominant role on the activity observed. In the case of gas-oil cracking, even if EFAL is active the textural characteristics of the zeolite (pore volume distribution) play a determinant role in the final behaviour of the sample.