The skeletal isomerization of n-butene to isobutene is a convenient way of producing isobutene. In this study we report 1-butene isomerization over aluminophosphate molecular sieves and silicoaluminate zeolites. Pore size, acidic strength, site density and channel tortuosity are important for the selectivity of isobutene. Medium pore size is suitable for the production of isobutene, The acidic sites of medium strength are responsible for the high selectivity of SAPO-11, Acidic sites of higher acidic strength and density yield more cracking products and less isobutene. Metal (Co, Mn, Zn) substitution in AlPO4-11 (MeAPO-11) shows higher selectivity for isobutene. Metal in the framework structure of MeAPO-11 is selective for isobutene. Metal ion exchanged into SAPO-11 or impregnated into SAPO-11 or AlPO4-11 is less-selective for isobutene. The weaker acidity and the increase of tortuosity by metal ion substitution improve the selectivity of isobutene. (C) 1999 Elsevier Science B.V. All rights reserved.