Unraveling the Active Site and Mechanism for C–S Bond Activation in Alumina-Supported Pt Catalysts: Ab Initio Insights into Catalytic Desulfurization

Understanding the active sites of metal/oxide catalysts is of great significance in heterogeneous catalysis. In this work, we performed periodic density functional theory calculations to study the C–S bond activation of CH₃SH on Pt/α-Al₂O₃ catalysts. Five different types of sites were investigated, which are single Pt-atom site in Pt₁/α-Al₂O₃, Pt(111) site in Pt slab/α-Al₂O₃, and top-edge, interface, and atop-Al sites in Pt nanorod/α-Al₂O₃, respectively. In contrast to the common thought that lower-coordinated atoms at the surface of small metal nanoparticles (NPs) would lead to the higher reaction activity, the present work clearly demonstrates that the coordination-unsaturated sites over Pt NPs have subtle influence on the C–S bond scission. On the basis of energetic analysis, we propose that the interfacial Pt (type I) site, summarized as the “Pt–Al” dual perimeter site, could be the active site for the C–S bond activation. The presence of alumina support adversely impacts catalytic performance of Pt nanoparticle itself but exerts positive influence along the Pt/alumina interfacial boundary. The origin of this positive effect on the C–S bond activation over the “Pt–Al” dual perimeter site can be understood from the electronic perspective, in which the active interfacial Pt atoms act as electron acceptors (Ptᵟ⁻) while alumina support acts as electron donors. The electron-rich property of Ptᵟ⁻ and the energy-level downshifting of the C–S antibonding orbitals of CH₃SH both facilitate the electron transfer from Pt to the C–S antibonding orbitals, leading to subsequent C–S bond cleavage. The electron transferred from the support to Pt is the determining factor to activate the C–S bond of CH₃SH and is dependent on the termination type of alumina. The present work provides geometric and electronic insights into the nature of active sites and sheds light on the design of more active metal/oxide catalysts toward catalytic desulfurization.