First-principles theoretical study on dry reforming of methane over perfect and boron-vacancy-containing h-BN sheet-supported Ni catalysts

Abstract

The entire reaction mechanism of the dry reforming of methane (DRM) as well as the competition processes over perfect and boron-vacancy-containing h-BN sheet-supported Ni-catalysts (labeled Ni₂/h-BN and Ni₂/h-BN-B–D) was studied by density functional theory calculations in the present work. Our calculation results show that B-defected h-BN strongly binds to the Ni₂ active sites (i.e., shows a strong metal-support interaction (SMSI) character) due to the better electron transfer between Ni₂ sites and the support. It was found that CH₄ is easier to activate than molecular CO₂. The activation of CO₂ occurs on the surface of Ni₂/h-BN through a direct route, whereas it is prone to follow a hydrogen-assisted path for Ni₂/h-BN-B–D via the COOH* intermediate, and the results show that the oxidant O* is easily formed on the surface of Ni₂/h-BN-B–D. It was also found that O* is the main oxidant agent for CH_x* intermediates through the CH₃–O oxidation mechanism. The reaction kinetic analysis indicated that the reverse water gas shift reaction (RWGS) is much more favorable than DRM (1.30 vs. 1.72 eV) over the Ni₂/h-BN system, whereas the RWGS and DRM are comparable on Ni₂/h-BN-B–D (1.77 vs. 1.66 eV), suggesting a high DRM activity on Ni₂/h-BN-B–D. Moreover, neither methane cracking nor a Boudouard reaction to form C* species is thermodynamically and kinetically unfavorable over Ni₂/h-BN-B–D; hence, Ni₂/h-BN-B–D has strong resistance to carbon deposition. Compared to Ni(111), both Ni₂/h-BN-B–D and Ni₂/h-BN show strong resistance to carbon deposition. Our results provide a further mechanistic understanding of the DRM over an Ni-based catalyst through the SMSI characteristic and the SMSI favors strong resistance to carbon deposition.