The gas-phase nitration of toluene was studied over a solid-acid zeolite beta catalyst with two different nitrating agents, HNO3 and N2O4, in a setup for continuous nitration. The selectivity of the reactions to 4-nitrotoluene was good, but the catalysts deactivated within a few hours. HNO3 gave higher yields than N2O4, but both HNO3 and N2O4 required a temperature lower than 160 degrees C to obtain acceptable yields and less oxidation products. At higher temperatures, catalyst deactivation was accelerated and the yield of nitrotoluene decreased. Lowering the feed rate of toluene led to a slower deactivation of catalyst. The deactivation of the catalyst was caused by pore blocking due to liquid reaction products as well as coke formation. Unlike in liquid-phase nitration, dealumination did not play a role in the deactivation of the catalyst, which could be regenerated by calcination in air. (c) 2007 Elsevier B.V. All rights reserved.