Catalytic oxidation of toluene was studied on zeolite-NaX, -HX and -NaY, alpha- and gamma-alumina, and ZrO2, with a self-oscillatory behavior observed on zeolite-NaX. The self-oscillatory behavior was examined by means of continuous flow reactions, temperature-programmed oxidation, infrared spectroscopy, and nitrogen adsorption. The self-oscillation was affected by temperature, catalyst acidity, and reactant composition, indicating its dependence on the imbalance between coke formation by toluene decomposition and coke removal by reaction with oxygen. From the mass spectrometric analysis of reaction data, one can deduce that the self-oscillation was caused by two periodically-repeated processes: the deactivation and the regeneration of zeolite-NaX. A stepwise mechanism was proposed to explain the self-oscillation by reversible pore-mouth fouling, (C) 2004 Elsevier B.V. All rights reserved.