Mixed Anion Control of the Partial Oxidation of Methane to Methanol on the β-PtO₂ Surface

Although the C-H bond of methane is very strong, it can be easily dissociated on the (110) surface of β-PtO₂. This is because a very stable Pt-C bond is formed between the coordinatively unsaturated Pt atom and CH₃ on the surface. Owing to the stable nature of the Pt-C bond, CH₃ is strongly bound to the surface. When it comes to methanol synthesis from methane, the Pt-C bond has to be cleaved to form a C-O bond during the reaction process. However, this is unlikely to occur on the β-PtO₂ surface: The activation energy of the process is calculated to be so large as 47.9 kcal/mol. If the surface can be modified in such a way that the ability for the C-H bond activation is maintained but the Pt-C bond is weakened, a catalyst combining the functions of C-H bond cleavage and C-O bond formation can be created. For this purpose, analyzing the orbital interactions on the surface is found to be very useful, resulting in a prediction that the Pt-C bond can be weakened by replacing the O atom trans to the C atom with a N atom. This would be a sort of process to make β-PtO₂ a mixed anion compound. Density functional theory simulations of catalytic reactions on the β-PtO₂ surface show that the activation energy of the rate-limiting step of methanol synthesis can be reduced to 27.7 kcal/mol by doping the surface with N.