TiO2 supported Pd nanoclusters with surface defects toward highly efficient hydrogenation of quinone to hydroquinone under mild conditions

•TiO2 supported Pd nanoclusters with surface defects (PdN/TiVo) were explored.•The properties of PdN/TiVo were analyzed and the coupled eutectic growth structure between Pd and TiO2 can be found.•PdN/TiVo catalysts exhibited considerably high yields and TOFs for the hydrogenation of TMBQ under mild conditions.•A mechanism for the synergistic catalytic hydrogenation of TMBQ over PdN/TiVo by metal Pd and oxygen vacancies was proposed. Hydrogenation of quinones is an efficient way to produce hydroquinone compounds. Typically, 2,3,5-trimethylhydroquinone (TMHQ), the key intermediate of vitamin E, can be produced via hydrogenation of 2,3,5-trimethylbenzoquinone (TMBQ). In order to effectively obtain the target products, the exploration of efficient heterogeneous catalysts is highly desired. In this study, supported Pd nanocluster catalysts (PdN/TiVo) were designed through a deposition-precipitation method over TiO2 support with surface defects (TiVo) to achieve high atomic utilization efficiency of the noble metal Pd under mild reaction conditions. The characterization showed that oxygen vacancies generated by H2 reduction on the support TiO2 acted as specific sites to promote the formation of the coupled eutectic growth structure composed of the active metal Pd and TiVo. The active metal Pd which not only exhibited high dispersion but also formed electron-rich active sites can activate H2 while the Ti3+ atoms at oxygen vacancy sites can adsorb the oxygen species from TMBQ, thereby a synergistic catalytic effect can be shown to enhance the adsorption and hydrogenation of C=O bonds. Thus PdN/TiVo revealed a high yield of TMHQ of 96% and TOF of 276 min−1 under a considerably wild condition (45°C, 0.2 MPa, 60 min). By comparison, state-of-the-art carbon based Pd catalysts (PdN/C) acquired only 29% yield and 41 min−1 TOF in the same way. The simultaneous engineering of Pd catalyst and oxygen vacancies on TiO2 offers a new strategy to develop efficient heterogeneous catalysts for hydrogenation of quinones. [Display omitted]