The theoretical calculation is performed to investigate the promotion mechanism of Cu surface on the over-thermal decomposition of SF₆ in gas-insulated equipment.
A 4*4*1 crystal cell was constructed by using a Cu(111) section with a thickness of 6.261 angstroms and a vacuum layer of 15 angstroms. According to adsorption and dissociation of O₂ on Cu(111) surface, the O(ads)-Cu surface model of fcc pre-adsorption site was constructed. And the reaction model is established by placing the Sulfur fluoride molecules above the O atom to simulate the Eley-Rideal mechanism. The geometry structures and transition states are calculated by Dmol³ module. The barriers of several vital reactions between sulfur fluorides and the pre-adsorbed oxygen atoms on the Cu surface  are calculated and compared with reactions with the same reactants in gas phase. The results indicate that the existence of Cu surface can significantly reduce the energy barrier of the reaction between SF₄ with O, while it does not change the barrier of the reaction between SF₂ with O, which shows the selectivity of the catalysis of Cu. The interface reaction can significantly reduce the energy barrier several reactions involving the low fluorine sulfides and oxygen atoms, which promote the decomposition process of SF₆ and threaten the safety operation of GIS and other gas-insulated equipment. Notably, the catalysis of Cu shows a certain degree of selectivity.

SF6,decomposition,surface reaction,transition state theory