Coking and deactivating experiments were carried out in a fixed-bed reactor for benzene oxidation to phenol (BTOP). The catalyst used in this study was HZSM-5 (SiO2/Al2O3 = 20) treated by high temperature steam at 700 degrees C. Then the catalysts undergoing different reaction time were analyzed and characterized. The amount of coke was measured by TG. The coke components were detected by infrared. At the same time, the main physics properties of the catalyst with coke deposition were characterized. The pores of the catalyst before and after coking were measured by N-2 adsorption at - 196 degrees C. The amount of hexane and cyclohexane adsorption was measured by weight continuous flow. The acid sites of Bronsted and Lewis were characterized by pyridine adsorption-infrared measurements. Our results show that the deactivation of ZSM-5 in the BTOP reaction system is caused by the coke deposition in the mouth of pores and blocking the pores of the catalyst. It can also be found that the present process agrees with most coking processes over ZSM-5 caused by organic compounds, the Bronsted acid sites are the active sites of the coking. (c) 2005 Elsevier B.V. All rights reserved.