Zeolite beta allows high yields and good selectivity in the batch nitration of toluene and chlorobenzene with acetyl nitrate. Deactivation of the HPB 1 zeolite beta catalyst takes place due to dealumination and the adsorption of acetic acid and acetic acid anhydride, which causes a decrease of the selectivity to 4-nitrotoluene in the nitration of toluene. Active reaction centres for the nitration are protonated aluminium centres in the zeolite framework, but not free aluminium species inside the reaction mixture. Nitrate or counter ions like sodium are not involved in the reaction mechanism. In the continuous liquid-phase nitration with acetyl nitrate, the zeolite beta catalyst enhanced the conversion of toluene only slightly, compared to the non-catalysed homogeneous reaction. With the less reactive substrate chlorobenzene, however, zeolite beta acted as an efficient catalyst in the continuous nitration with acetyl nitrate. (c) 2007 Elsevier B.V. All rights reserved.