Acidity and catalytic properties of MeAPO-5 molecular sieves

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