DFT transition state study of the catalyzed oxidation of methane on SnO2 surfaces

Along this research the (110), (101) (200) and (211) surfaces were chosen to be studied by considering their atomic surface density. The surfaces were studied using CASTEP for the transition state search by DFT calculations, the initial coordinates that establish the SnO₂-Methane distance were obtained with Adsorption Locator, a software able to calculate adsorption configurations using Monte Carlo methods. The results show that in terms of overall energy change, surface (101) presents the most favorable configuration with an exothermic total-energy change (form CH₄ on the surface to a CO and H₂O molecules on the surface) of − 18.47 kcal/mol, being the worst case the CH₄ on a (200) surface with an endothermic total energy-change of 128.86 kcal/mol. In terms of the TS energy, the (101) surface remains as the most favorable system with energy maximums on the TS reaction path of 99.25 kcal/mol for the dissociation and adsorption of the CH₄ molecule on the surface, and a maximum of 266.42 kcal/mol for the desorption and formation of the CH₄ and H₂O molecules on the SnO₂ surface.