ACIDITY AND CATALYTIC PROPERTIES OF MEAPO-5 MOLECULAR-SIEVES

Molecular sieves of AlPO4-5 type containing ions of various metals iso morphously incorporated into the framework have been characterized by temperature programmed desorption of ammonia, infrared spectroscopy, a nd catalytic effectiveness in the conversion of methanol. The incorpor ation of metal ions (Mn, Co, Ni, Mg, Zn, Zr, and silicon) gives rise t o the formation of bridged hydroxyl groups (Bronsted sites) of differe nt acidic strength. Simultaneously, Lewis sites of low as well as of h igh acidity are generated. Catalysis of C-C bonding reactions is conne cted to the presence of acidic sites of higher strength. Best catalyti c results with respect to the formation of lower olefins are achieved with NiAPO-5 varieties, which contain a sufficiently high density of B ronsted sites of moderate strength and comparatively small portions of strong acid Lewis sites. (C) 1998 Elsevier Science B.V.