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To produce gasoline that could meet the sulfur content demand of increasingly stringent environmental regulations is a great challenge for worldwide oil refining and petrochemical industry,which is especially urgent in our country.Among all the sulfur-containing compounds,thiophene is the most difficult composition to desulfurize for the low reaction activity of C-S bond in thiophene.Besides,MoS2 was the most widely used catalysts in hydrodesulfurization(HDS)industry,and current researches have concentrated on how to improve the HDS activity and selectivity of MoS2 by doping another transition metal addictive.This work mainly referred to the thiophene HDS reaction mechanisms over 50%Ni substituted MoS2 catalyst.In order to investigate thiophene HDS reaction mechanism over 50%Ni-MoS2 catalyst,detailed thiophene HDS processes over 50%Ni-MoS2 were studied by density functional theory(DFT+D) calculations.All calculations were performed with DMol3 program1,2 in fine accuracy.In particular,Grimme method3 was employed for dispersion corrections(DFT+D correction).In addition,Krebs et al 4 found that Ni is more stable on Mo edge than on S edge of MoS2 catalyst.Thereby we focused on the Mo edge of 50%Ni-MoS2 catalyst with 25%sulfur coverage.The transition states in current study have been proved by imaginary frequency.Firstly,adsorption performance of thiophene at the Mo edge of 50%Ni-MoS2 was studied,which turned out that the most stable configuration was S atom bonding with the bare Ni atom at the edge surface.Secondly,adsorption properties of involved intermediates and possible products were considered.Finally,all the possible reaction routes were calculated and the corresponding transition states were searched.The results showed that there exist three kinds of favorable products,which were CH3CH2CH2CH3,CH3CH=CHCH3,and CH2=CHCH2CH3,respectively.More importantly,the reaction barrier values along the reaction pathways revealed that the hydrodesulfurization of thiophene was easier to occur over 50%Ni-MoS2 catalysts than on pure MoS2 catalysts.