Comparison of reaction mechanism of thiophene hydrodesulfurization on Au₁₃ and Pt₁₃ clusters

The behaviors of thiophene adsorption and hydrodesulfurization on cubic octahedral M₁₃ (M=Au, Pt) clusters were investigated by density functional theory. The results show that the adsorption energy of thiophene on Pt₁₃ is higher than that on Au₁₃; on the Au₁₃ cluster, the Hol-tri site is most stable for the thiophene adsorption with ring, whereas on the Pt₁₃ cluster, the Hol-quadr site is most stable. By the indirect desulfurization mechanism, the desulfurization is achieved probably via the cis-hydrogenation; the removal of C-S is the rate-determining step. By the direct desulfurization mechanism, the HS hydrogenation turns to be the rate-determining step. The desulfurization is most likely via the direct desulfurization mechanism, which exhibits much lower activation energy than the indirect desulfurization mechanism. The energy change for thiophene desulfurization on the Au₁₃ cluster is exothermic, whereas on the Pt₁₃ cluster it is endothermic; as a result, the hydrodesulfurization on Au₁₃ is much easier than that on Pt₁₃.