Impact of Ni particle size on CO_(2)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 CO_(2)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 CO_(2)activation and the formation of CO during the DRM reaction.It is found that CO_(2)is more inclined to undergo chemisorption on Nix/MgO before activation.With the variation in particle size,the main activation pathway of CO_(2)on the catalyst changes.On the smallest Ni13/MgO,CO_(2)tends to directly dissociate,while on the larger Ni25/MgO and Ni37/MgO,the hydrogenation dissociation of CO_(2)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.