Friedel-Crafts alkylations are important class of reactions in the production of chemicals of industrial relevance. In the current work, selective monobenzylation of naphthalene with benzyl chloride was achieved at 80 degrees C by using a novel mesoporous solid acid catalyst UDCaT-4 which is a hexagonal mesoporous silica incorporating persulfated alumina and zirconia. It is found that UDCaT-4 exhibit superior catalytic activity than persulfated alumina and zirconia. The catalyst is reusable. The reaction was 100% selective towards monobenzylated naphthalene without any dibenzylation. The Langmuir-Hinshelwood model with weak adsorption of reactants and products was found to validate the kinetics. The energy of activation is 26.0 kcal/mol. (c) 2006 Elsevier B.V. All rights reserved.