Construction of Highly Active Pd–Ti³⁺ Sites in Defective Pd/TiO₂ Catalysts for Efficient Hydrogenation of Styrene–Butadiene–Styrene

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.

Electron repulsion tuned electronic structure of TiO2 by fluorination for efficient and selective photocatalytic ammonia generation

“…Numerous studies have shown that the low valence metal centers of transition metal oxides can serve as active sites for inducing localized electron reduction of N 2 . 15 Recently, Hirakawa et al found that Ti 3+ species in TiO 2 can provide electrons for the anti-bonding π* orbitals of N 2 , which greatly facilitates the breaking of NN bonds. 16 Han et al also demonstrated that the high concentration of Ti 3+ sites in C-TiO x is the main reason for the enhanced N 2 photoreduction activity.…”