Alkylation of biphenyl with propylene in gas phase was carried out over two zeolites: MCM-22 and ITQ-2. The influence of zeolite structure on reaction activity and selectivity is discussed. The alkylation activity follows the order: ITQ-2 > MCM-22. The influence of the change in the morphology in MCM-22 to ITQ-2 has been studied and it has been observed that, under the reaction conditions used here, the reaction takes place mainly on the external surface, which indicates that the dimensions of 10 MR channels inhibit the diffusion of the bulky reactants inside the zeolitic pores and, also, explains the high o-IPBP selectivity observed. (C) 2007 Elsevier B.V. All rights reserved.