The interaction mechanisms of CO2 with CH3 and H on Cu(1 1 1) surface in synthesis of acetic acid from CH4/CO2 are systematically investigated by the first-principle DFT-GGA calculations. Four possible reaction pathways are proposed, and the detailed mechanisms and kinetics are discussed. Our results show that all products are formed by gaseous CO2 and adsorbed CH3 and H through the Eley-Rideal (E-R) mechanism. It is found that the values of the activation barrier for four different pathways are in the order of CH3COO-Cu < HCOO-Cu < HOOC-Cu < CH3OCO-Cu, suggesting that CO2 insertion into Cu CH3 bond to form CH3COO-Cu is the most advantageous in dynamics among all four reaction pathways, and the corresponding activation barrier of the rate-controlled step is 85.2 kJ mol(-1). The insertion of CO2 into Cu H bond to form HCOO-Cu is secondly preferential pathway favored in dynamics. Therefore, H3CCOO is the main product, HCOO is a primary side product, and H3COCO are not obtained as it is inhibited by dynamics in comparison with other pathways. Above calculated results are in accordance with the experimental results, which can provide a new theoretical guidance for the direct synthesis of oxygenated compounds from CH4 and CO2. (C) 2012 Elsevier B.V. All rights reserved.