Impact of Ni particle size on CO2 activation and CO formation during reforming process: A density functional theory study

In recent years, the dry reforming of methane (DRM) reaction has gained widespread attention due to its effective utilization of two major greenhouse gases. Supported Ni-based catalysts for DRM exhibit a strong dependence on particle size, however, the reaction mechanisms involved remain unclear. In this work, the effect of metal particle size on CO2 activation and CO formation was explored in the DRM reaction using the density functional theory. Nix/MgO (x = 13, 25, 37) was constructed to investigate the CO2 activation and the formation of CO during the DRM reaction. It is found that CO2 is more inclined to undergo chemisorption on Nix/MgO before activation. With the variation in particle size, the main activation pathway of CO2 on the catalyst changes. On the smallest Ni13/MgO, CO2 tends to directly dissociate, while on the larger Ni25/MgO and Ni37/MgO, the hydrogenation dissociation of CO2 is more kinetically favorable. Compared to Ni13/MgO and Ni37/MgO, the oxidation of surface C atoms and the oxidation of CH occur more readily on Ni25/MgO. This indicates that C atoms are less likely to form on Ni25 particle and are more easily to be oxidized. To some extent, the results suggest that Ni25/MgO exhibits superior resistance to carbon formation.