Metal-promoted mesostructured silica nanoparticles (MSN) have been studied for CO2 methanation under atmospheric pressure. In term of activities, high activity was observed on Rh/MSN, Ru/MSN, Ni/MSN, Ir/MSN, Fe/MSN and Cu/MSN at and above 623 K. However, on an areal basis, Ni/MSN was the most active catalyst, while Ir/MSN was the poorest catalyst. The catalysts have also been studied for elucidation of the role of each metal, MSN and metal/MSN in CO2 methanation by in situ FTIR spectroscopy studies. Firstly, CO2 and H-2 was adsorbed and dissociated on metal sites to form CO, O and H atoms, followed by migration onto the MSN surface. The dissociated CO then interacted with oxide surfaces of MSN to form bridged carbonyl and linear carbonyl, while the presence of H atom facilitated the formation of bidentate formate. These three species could be responsible for the formation of methane. However, the bidentate formate species could be the main route to formation of methane. MSN support has been found to play an important role in the mechanism. MSN support served the sites for carbonyl species which act as precursors to methane formation. These results provided new perspectives in the catalysis, particularly in the recycling of CO2. (C) 2014 Elsevier B.V. All rights reserved.