Highly selective synthesis of diphenylmethane (DPM) was carried out by Friedal-Crafts benzylation of benzene using benzyl chloride (BC) as alkylating agent in the presence of a flow of nitrogen under liquid phase reaction conditions over novel mesoporous SO42-/Al-MCM-41 catalysts with different Si/Al ratios. For these reactions, the influences of various reaction parameters, such as different catalysts, reaction temperature, time, mmol ratios of reactants and recyclability are discussed. With increasing the Si/Al ratios of SO42-/Al-MCM-41 catalysts from 21 to 83, the conversion of BC and selectivity of DPM decreased because the number of Lewis acid sites in SO42-/Al-MCM-41 catalysts are found to decrease almost linearly with increasing ratios of Si/Al. Further the catalytic results were compared with those obtained by using 0.8N sulfuric acid, different Si/Al ratios of Al-MCM-41, HY, HP, HM and H-ZSM-5 zeolites. From the comparison of the results, SO42-/Al-MCM-41(21) is found to be a highly active and recyclable heterogeneous catalyst for the highly selective synthesis of DPM. Thus, the selectivity of DPM in SO42-/Al-MCM-41(21) is higher than that in other SO42-/Al-MCM-41 (Si/Al = 42 and 83), Al-MCM-41 (Si/Al = 21, 42 and 83), HY, H beta, HM and H-ZSM-5. (c) 2005 Elsevier B.V. All rights reserved.