The adsorption, thermal reaction, and photoreaction of methyl iodide on powdered Ag-covered TiO2 (Ag/TiO2) were studied using Fourier transform infrared spectroscopy. The Ag was deposited on TiO2 by photoreduction of AgNO3. The resultant Ag/TiO2 was analyzed by TEM, ESCA, and AA. Evolution of methane was observed in the absence of oxygen for thermal reaction at temperature above 623 K. Photoreaction showed the enhancement in CH3I dissociation due to the presence of Ag on TiO2 surface. In this reaction, methyl radicals produced were recombined to form ethane molecules over the Ag/TiO2. The same reactions in the presence of oxygen change their pathways completely yielding oxygen-containing products. In thermal reaction, CO(g), CO2(g), CH2O(g), (CH3)(2)O-(g), and H2O(g) were observed. On the other hand, in the photochemical reactions, CO2(g), H2O(g), and surface formate groups were produced. Possible pathways for present thermal and photochemical reactions are discussed and the results were compared with that obtained using bare TiO2. (C) 2004 Elsevier B.V. All rights reserved.