Enhanced methane adsorption and dissociation on Co-doped VO\(_{2}\)(110) surface: a DFT + U study

Abstract

We report first-principles density-functional theory (DFT with Hubbard U) investigation of the adsorption and dissociation mechanisms of CH\(_{4}\) on the VO\(_{2}\) surface. We have considered three types of VO\(_{2}\) surfaces, namely, the pristine defect-free, oxygen vacancy, and co-doped VO\(_{2}\)(110) surfaces. The doped surface is identified as the most suitable for CH\(_{4}\) dissociation reaction due to enhanced stability of atomic and molecular radicals involved in the proposed CH\(_{4}\) dissociation reaction. We obtained adsorption, dissociation, and interaction energies, as well as the reaction enthalpies of the dissociation intermediates. These parameters were used to identify the energetically most favorable reaction pathway for CH\(_{4}\) dissociation via the thermochemistry approach. Four possible reaction pathways were considered: CH\(_{4}\) \(\rightarrow \) CH\(_{3}\) + H; CH\(_{4}\) \(\rightarrow \) CH\(_{2}\) + 2H; CH\(_{4}\) \(\rightarrow \) CH + 3H; and CH\(_{4}\) \(\rightarrow \) C + 4H. Based on the reaction enthalpy (\(\Delta H\)), we found that the pathways CH\(_{4}\) \(\rightarrow \) CH\(_{3}\) + H and CH\(_{4}\) \(\rightarrow \) C + 4H are energetically favorable with \(\Delta \)H of −0.16 eV and −2.58 eV, respectively. In contrast, the reaction pathways CH\(_{4}\) \(\rightarrow \) CH\(_{2}\) + 2H and CH\(_{4}\) \(\rightarrow \) CH + 3H are endothermic with positive \(\Delta H\), suggesting that the dissociation pathways are energetically unfavorable. Electronic structure analysis shows charge transfer from the adsorbed species to the surface and hybridizations of p orbitals of C and O, and Co-d and C-p orbitals. Charge transfer and hybridization are the electronic origin of the stability of the dissociated or adsorbed products. Our study demonstrates that Co doping enhances the catalytic dissociation of CH\(_{4}\) on the VO\(_{2} \)(110) surface thus underlying the role of defect engineering via metal doping in surface catalysis while also proposing Co-doped VO\(_{2} \)(110) surface as a promising candidate material for CH\(_{4}\) dissociation and hydrogen production.