Balancing d-π/d-π* Interactions: Valence-Engineered Pd/TiO2 for Photocatalytic Acetylene Semi-Hydrogenation

en This link goes to a English section zh This link goes to a Chinese section Photocatalytic acetylene (C 2 H 2 ) semihydrogenation is a green route for ethylene (C 2 H 4 ) production, yet the activity–selectivity trade-off caused by imbalanced adsorption/activation of reactants and products remains a core challenge. Herein, we realize precise regulation of Pd oxidation states (Pd 0 , Pd δ + , and Pd 2+ ) on anatase TiO 2 nanocubes via a mild reduction strategy, fabricating a Pd δ + /TiO 2 photocatalyst with intermediate valence of Pd sites. Systematic characterizations and theoretical calculations reveal that Pd δ + optimizes the d-π/d-π* orbital interactions between Pd and C 2 H 2 /C 2 H 4 , achieving a moderate adsorption strength that balances efficient C 2 H 2 activation and rapid C 2 H 4 desorption. Pd 0 causes overadsorption/overhydrogenation, whereas Pd 2+ leads to weak substrate activation. Consequently, Pd δ + /TiO 2 achieves nearly 100% C 2 H 2 conversion and ∼90% C 2 H 4 selectivity, with a record-high turnover number (TON) of ∼4.1 × 10 4 and excellent cycling stability. This work clarifies the electronic mechanism of Pd valence engineering in carrier dynamics and modulating orbital hybridization, providing a new strategy for the rational design of C 2 H 2 semihydrogenation photocatalysts. 摘要 en This link goes to a English section zh This link goes to a Chinese section 光催化乙炔(C 2 H 2 )半加氢是一种制备乙烯(C 2 H 4 )的绿色路径,但反应物与产物吸附与活化不均衡引发的活性-选择性权衡问题仍是核心难题。本文通过温和还原策略,在锐钛矿二氧化钛纳米立方体上实现钯氧化态(Pd 0 、Pd δ + 、Pd 2+ )的精准调控,制备出活性位点为中间价态钯的 Pd δ + /TiO 2 光催化剂。系统表征与理论计算结果表明,Pd δ + 能够优化钯与C 2 H 2 /C 2 H 4 之间的d-π/d-π* 轨道相互作用,形成适中的吸附强度,兼顾高效活化乙炔与乙烯快速脱附, Pd 0 会造成吸附过强并引发过度加氢,而Pd 2+ 对底物活化能力较弱。因此,Pd δ + /TiO 2 可实现接近 100% 的乙炔转化率和约 90% 的乙烯选择性,周转数(TON)高达4.1 × 10 4 ,同时具备优异的循环稳定性。该研究阐明了调控钯价态对载流子动力学及轨道杂化进行调控的电子作用机制,为乙炔半加氢光催化剂的合理设计提供了新思路。