The influence of carbon dioxide and ethane on the conversion of methane to aromatics over MO/SiO2/H-ZSM-5 was investigated at 973 K and 1.2 bar. The immediate effects of carbon dioxide introduction (CO2/CH4 = 0.04) include a slight increase in the rates of methane conversion and hydrogen production, but a slight decrease in the rates Of C-2+ production. In addition, carbon dioxide introduction improved catalyst stability for methane conversion and C-2+ production. Conversely, methane conversion was completely suppressed in the presence of carbon dioxide and ethane (CO2/C2H6/CH4 = 0.04/0.11/1). Characterization of as-prepared and spent catalyst samples via X-ray diffraction, Al-27 MAS NMR, nitrogen adsorption, and temperature-programmed oxidation (TPO) reveals that the accumulation of coke decreases the accessible micropore surface area and volume, distorts the zeolite lattice, and ultimately, deactivates the catalyst. While carbon dioxide addition inhibits the rate and consequences of coke accumulation, ethane addition accelerates the rate and consequences of coke accumulation. (C) 2004 Elsevier B.V. All rights reserved.