Supported Pt Metal Clusters with Different Sizes on TiO2 Nanosheets: Efficient Catalytic Dehydrogenation of Dodecahydro-N-ethylcarbazole

An essential step in developing heterogeneous metal catalysts is to locate their active catalytic sites. In contrast to large metal nanoparticles (NPs) and isolated metal single-atom catalysts (SACs), supported metal clusters (SMCs) possess unique electronic and geometric features that contribute to their improved catalytic properties. In this study, the loading amount of metal Pt was quantified as 2.5 wt %, and the Pt/TiO2 catalysts containing Pt clusters with sizes ranging from 1 to 4 nm were obtained in order to analyze the influence of the Pt cluster size on the dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NECZ). The optimal dehydrogenation performance was achieved on the 2.5PT-6.5-3.0 (Pt-1.72) catalyst with an average Pt cluster size of 1.72 ± 0.20 nm, and there were almost no byproducts. Besides, the kinetic analysis demonstrated that the third net stoichiometric reaction was the rate-limiting step, and the k3 values were significantly improved with the appropriate Pt cluster size. Furthermore, a volcano plot existed between the Pt cluster sizes and the specific activities, where the Pt-1.72 catalyst occupied the extreme point (4.87 molNECZ/molPt·min). Combining the experimental results and previous reports, it could be concluded that it was important to regulate the Pt cluster size in the 1–2 nm range, so the catalysts with 1–2 nm Pt clusters were focused to be explored. It could be revealed that the different Pt cluster sizes caused the change in the catalyst structures, and only the catalyst with the suitable Pt cluster size could exhibit suitable adsorption and activation capacity for the reactants during 12H-NECZ dehydrogenation, achieving optimal catalytic properties. DFT calculations also confirmed that the suitable Pt cluster size enhanced the efficiency of three dehydrogenation steps, consistent with the experiments.