Effects of modification of cesium ion-exchanged zeolite X (Cs-X) with Cs2O and zirconium borate (ZrB2O5) on the catalytic activity in the side-chain alkylation of toluene to styrene and ethylbenzene were studied to prepare an effective catalyst for styrene production. The toluene conversion to styrene and ethylbenzene increased but the selectivity to styrene decreased on modification of Cs-X with Cs2O. For the toluene conversion, the optimum loading of Cs2O was in the range ca. 1-5 wt%. Modification of Cs2O/Cs-X with ZrB2O5 increased both toluene conversion and styrene selectivity. Characterization of acidic and basic properties by IR spectroscopy of adsorbed pyridine and CO2 indicated that basic properties were markedly enhanced but acidic properties were not changed by modification of Cs-X with Cs2O. It is suggested that the enhancement of toluene conversion by modification with Cs2O is due to the generation of strong basic sites which promote the activation of toluene by an abstraction of a proton from methyl group. Modification with ZrB2O5 facilitates the formation of formaldehyde to increase the toluene conversion and suppresses the transfer hydrogenation of styrene with methanol, the main pathway to ethylbenzene, to increase the styrene selectivity. (C) 2013 Elsevier B.V. All rights reserved.