The interaction mechanisms of dry reforming of methane, especially in the part of CO2 activation on the reduced NiO-MgO catalyst, have been systematically investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations. Based on the results, it is indicated that, what more favorable for CO generation is gaseous CO2 reaction with deposited C intermediates, namely E-R type mechanism, rather than CO2 direct dissociation to form CO and atomic O. In addition, with the help of H species, monodentate carbonate, which derives from the adsorbed CO2 on the MgO surface, can be also activated and hydrogenated dissociation to generate CO. (C) 2017 Elsevier B.V. All rights reserved.