A DFT study of CH4 adsorption on OMS-2 (1 1 0) surface with different types of oxygen vacancies

Abstract

Cryptomelane-type octahedral molecular sieves (OMS-2) is considered as a promising non-precious metal catalyst, and its catalytic activity is largely related to oxygen vacancies (OVs). Hence, the effects of two types of OVs on CH4 adsorption on the surface of OMS-2 (110) were investigated based on density function theory (DFT). The cohesive energy, OVs formation energy, adsorption energy, density of states and Bader charge were calculated. The results show that OVs will preferentially form at sp3 oxygen sites on the surface. Methane tends to adsorb at the K site with three H atoms facing the surface. When the O-sp3 vacancy is introduced, the adsorption capacity of (110) surface for methane is enhanced, the electron transfer is increased, and the degree of CH activation is higher. Moreover, the adsorption capacity is further strengthened with increasing the number of O-sp3 defects. Conversely, the introduction of sp2 oxygen defect hinders the adsorption of methane by the catalyst due to the rearrangement of surface atoms. These conclusions can provide theoretical guidance for the development of efficient methane catalysts.