Comparative DFT study on the reaction mechanism of dry reforming of methane over Ni (111), Ni@Co (111) and Co (111) surface

Abstract

Ni-Co bimetal is a considerably promising catalyst to apply in DRM process, and the unique Ni@Co core–shell structure maybe improve the activity and stability, but the reaction pathways and underlying mechanism on Ni@Co surface at the micro level need to be further uncovered. In current work, the adsorption of intermediates and the elementary reactions were systematically investigated based on Density Functional Theory calculations, and reason for Ni@Co core–shell structure enhancing the catalytic performance was obtained by comparing the related energies on Ni (111), Ni@Co (111) and Co (111) surface. Results suggested that CH₄ dehydrogenation is the rate-determining step for CH₄ activation, and the activation energy barrier is 1.43 eV on Ni@Co (111) surface, higher than 1.27 eV on Ni (111) and 1.31 eV on Co (111) surface. Compared with pure Ni and Co catalyst, Ni@Co core–shell catalyst could reduce the carbon formation by inhibiting the CH₄ dissociation into C. Moreover, CO₂ direct dissociation is dominating path for CO₂ activation process. The activation energy barrier is 0.56 eV on Ni (111) surface, and it is further decreased to 0.36 eV on Co (111) surface and 0.22 eV on Ni@Co (111) surface. Ni@Co core–shell structure could promote the CO₂ activation to produce more oxygen species to the oxidize CH and C. Moreover, Ni@Co core–shell structure is also contribute to the elimination of carbon deposited by promote C oxidation and hydrogenation. Furthermore, Ni@Co core–shell structure could also reduce the activation energy barrier of CO and H₂ formation, and increase the activation energy barrier of H₂O formation, which could suppress the generation of by-products and improve the selectivity of target products.