The catalytic performance of bimetallic chromium-copper supported over untreated ZSM-5 (Cr-Cu/Z), ZSM-5 treated with silicon tetrachloride (Cr-Cu/SiCl4-Z) and ZSM-5 treated with steam (Cr-Cu/H2O-Z) is reported. The activity is based on the combustion of ethyl ethanoate and benzene at a feed concentration of 2000 ppm and a gas hourly space velocity (GHSV) of 32000 h(-1). Due to higher reactivity and larger molecular size compared with that of water molecules, SiCl4 reacted at the external surface of ZSM-5 crystals. Cr-Cu/SiCl4-Z and Cr-Cu/H2O-Z both gave slightly lower conversion and carbon dioxide yield compared with Cr-Cu/Z. This was attributed to larger active metal crystallites formed in the mesopores and narrowing pore mouth and pore intersection by extraframework species. Cr-Cu/SiCl4-Z and Cr-Cu/H2O-Z both had reduced concentration and strength of acid sites, thus making them less susceptible to deactivation by coking. The coke accumulated by these two catalysts was relatively softer and more easily decomposed in oxygen during catalyst regeneration. (C) 2004 Society of Chemical Industry.