Abstract: A selective, simple and efficient process for single step alkylation of ethylbenzene with ethanol, in the presence of catalytically effective amount of pore size controlled and preconditioned gallo aluminosilicate zeolite is disclosed. The process comprises subjecting a feed mixture of ethylbenzene, ethanol and optionally one or more of the reaction product/byproduct in contact with the catalyst under a chosen set of conditions. The product para-diethylbenzene can be recovered directly from the reactor effluent, by simple distillation, avoiding complicated separation processes, with a high purity sufficient for commercial application.