PREPARATION AND PROPERTIES OF NEW ACID CATALYSTS OBTAINED BY GRAFTINGALKOXIDES AND DERIVATIVES ON THE MOST COMMON SUPPORTS - NOTE-I - GRAFTING ALUMINUM AND ZIRCONIUM ALKOXIDES AND RELATED SULFATES ON SILICA

In this paper we will show that it is possible to modify the acid prop erties of a surface, rich of hydroxyl groups by grafting in suitable c onditions metal alkoxides, such as aluminium and zirconium alkoxide. D epending on the amount of metal alkoxide it is possible to obtain, aft er steaming of the surface and calcination, different coverage degree up to the monolayer. Iteration of the grafting technique gives a multi layer, completely modifying the original surface. Grafting aluminium a nd zirconium alkoxides pre-treated in homogeneous phase with pure sulp huric acid leads to catalysts with very strong acid sites on the surfa ce. The acidic properties of the catalysts obtained by grafting alumin ium and zirconium alkoxides and their sulphate derivatives on silica h ave been characterized by different techniques such as: potentiometric titrations, Temperature Programmed Desorption of organic bases and di fferential calorimetry to evaluate the density of the active sites and their strength. Prepared catalysts were proven in test reactions such as methanol dehydration and hydrocarbon isomerization and cracking. W e have shown that sulphated catalysts have very strong acid sites of b oth the Bronsted and Lewis type, able to promote hydrocarbon isomeriza tion and cracking at the relatively low temperature of 250 degrees C. (C) 1998 Elsevier Science B.V.