Strong electronic metal-support interactions as a strategy for boosting selective hydrogenation of resorcinol to 1,3-cyclohexanedione

Strong electronic metal-support interactions (EMSIs) present in supported metal catalysts play a crucial role in determining their catalytic performances. In this study, we demonstrate the successful utilization of nanosized TiO2 (∼8 nm) as a carrier to achieve highly dispersed Pd clusters (∼0.59 nm) with robust EMSIs, even at a high Pd loading of 5 wt%. The presence of surface defects in nanosized TiO2 facilitates the anchoring of Pd clusters onto the support surface, leading to enhanced EMSIs between TiO2 and Pd. The prepared Pd/TiO2 catalyst delivers drastically improved catalytic property in the hydrogenation of resorcinol (RES), achieving >99 % conversion and >99 % selectivity towards 1,3-cyclohexanedione (1,3-CHD) within 60 min at 2 MPa hydrogenation pressure and 373 K. This performance is superior to that of Pd nanoparticles on TiO2 support with a larger particle size of ∼200 nm, which only achieves 80 % conversion and 37 % selectivity to 1,3-CHD. Both experimental data and theoretical calculations confirm that TiO2 donates electrons to the Pd clusters, thereby enhancing the hydrogenation properties of RES. Specifically, the electron-deficient TiO2 favors the adsorption and activation of phenoxy anion, while the electron-enriched Pd induces a nonplanar conformation of the adsorbed RES molecules and facilitates the electrophilic attack of adsorbed hydrogen on RES by weakening the strength of hydrogen adsorption. Furthermore, the Pd/TiO2 catalyst exhibits excellent recyclability, maintaining its efficiency over 7 cycles, thanks to the stabilizing effect of nanosized TiO2 on Pd clusters. The simple design strategy presented in this work enables the development of supported metal catalysts with significant EMSIs and is expected to attract more attention in future research.