Coupled semiconductor (CS) Cu/CdS-TiO2/SiO2 photocatalyst was prepared using a mutli-step impregnation method. Its optical property was characterized by UV-vis spectra. BET, XRD, Raman and IR were used to study the structure of the photocatalyst. Fine CdS was found dispersed over the surface of anatase TiO2/SiO2 substrate. Chemisorption and IR analysis showed methane absorbed in the molecular state interacted weakly with the surface of catalyst, and the interaction of CO2 with CS produced various forms of absorbed CO2 species that were primarily present in the form of formate, bidentate and linear absorption species. Photocatalytic direct conversion of CH4 and CO2 was performed under the operation conditions: 373 K, 1:1 of CO2/CH4, 1 atm, space velocity of 200 h(-1) and UV intensity of 20.0 mW/cm(2). The conversion was 1.47% for CH4 and 0.74% for CO2 with a selectivity of acetone up to 92.3%. The reaction mechanisms were proposed based on the experimental observations. (C) 2004 Elsevier B.V. All rights reserved.