THE ROLE OF SHAPE SELECTIVITY AND INTRINSIC SELECTIVITY OF ACIDIC SITES OF THE CATALYSTS IN THE SKELETAL ISOMERIZATION OF N-BUTENES

The effect upon kinetic behaviour (activity and selectivity) of the ph ysical properties (pore volume distribution) and acidic characteristic s (nature of acidic sites and acidic strength distribution) of acidic catalysts in the skeletal isomerization of n-butenes has been studied. The catalysts studied are the following: gamma-alumina, alumina modif ied by introduction of F, Cl and Br, silica-alumina, HZSM-5 zeolite-ba sed catalyst and SAPO-34-based catalyst. It has been proven that the s electivity of acidic catalysts towards the skeletal isomerization of n -butenes is the result of a compromise between pore shape selectivity and intrinsic selectivity of the acidic sites of different strength, t his latter property being more significant. Strong acidic sites are ne eded for the skeletal isomerization, but sites which are too strong pr oduce important amounts of byproducts. A chlorinated alumina is a high ly active and selective catalyst for skeletal isomerization. (C) 1998 SCI.