During the conversion of methane to benzene in the absence of oxygen over a 2 wt% Mo/H-ZSM-5 catalyst at 700 degrees C, three different types of surface carbon have been observed by X-ray photoelectron spectroscopy : adventitious or graphitic-like C (284.6 eV), carbidic like C (282.7 eV), and hydrogen-poor sp-type C (283.2 eV), where the C Is binding energies for the respective forms of carbon are given in parentheses. Pretreatment of the catalyst at 700 degrees C in CO also resulted in a strong signal at 283.2 eV; thus, the species responsible for this signal appears to be different from the usual aromatic-type coke. The coke with dominantly sp hybridization is concentrated on the external surface of the zeolite and is responsible for the gradual deactivation of the catalyst.