Construction of Highly Active Pd–Ti<sup>3+</sup> Sites in Defective Pd/TiO<sub>2</sub> Catalysts for Efficient Hydrogenation of Styrene–Butadiene–Styrene
Shidong Wang, Bingqing Ge, Zongxuan Yang, Hongwei Zhang, Qin Yang, Cejun Hu, Xiaojun Bao, Pei Yuan
Abstract
Defect-rich Pd/TiO 2 catalysts are intensively adopted in heterogeneous hydrogenation reactions; however, the complexity of the defect structure makes it difficult to precisely identify which Pd-defect combination dominates the catalytic activity. Herein, defective TiO 2 nanoflakes with tunable ratios of Vo to Ti 3+ defects were synthesized and used to construct Pd–Vo and Pd–Ti 3+ active sites after loading Pd to investigate the role of defects in regulating the structural and catalytic properties of defective Pd/TiO 2 catalysts. Combining the experimental results and theoretical calculations, we reveal that both Vo and Ti 3+ defects act as the electron donors for Pd and induce the strong metal–support interaction. When compared to the Vo defect, the Ti 3+ defect behaves more significantly and donates more electrons, causing the Pd species on the catalysts to be better dispersed and more rich in electrons. These unique features endow the Pd–Ti 3+ active centers with enhanced adsorption–activation ability toward C═C and H 2 as well as reduced energy barrier of the rate-limiting step, thus improving the intrinsic activity. The Pd–Ti 3+ site manifests a high turnover frequency of 348 h –1 and hydrogenation degree of 97% for hydrogenation of C═C in styrene–butadiene–styrene, which significantly outperforms the Pd–Vo site (254 h –1 and 78%) and Pd nanoparticle (217 h –1 and 53%). This work provides deep insight into the role of defects in regulating the properties of metal active sites, which can be used to guide the development of high-performance Pd/TiO 2 catalysts for versatile applications.