Modulating the Coverage of Adsorbed Hydrogen via Hydrogen Spillover Enables Selective Electrocatalytic Hydrogenation of Phenol to Cyclohexanone.

Selective electrocatalytic hydrogenation (ECH) of phenol is a sustainable route to produce cyclohexanone, an industrially important feedstock for polymer synthesis. However, attaining high selectivity and faradaic efficiency (FE) for cyclohexanone remain challenging, owning to over-hydrogenation of phenol to cyclohexanol and competition of hydrogen evolution reaction (HER). Herein, by employing hydrogen spillover effect, we modulate adsorbed hydrogen species (H) coverage on Pt surface via migration to TiO in an anatase TiO-supported Pt catalyst. In ECH of phenol, a high selectivity (94 %) and good FE (63 %) for cyclohexanone are obtained, showing more advantageous performance compared with previous reports. Cyclic voltammetry (CV) tests and electrochemical Raman spectroscopy reveal that H migrated from Pt to TiO. We propose that TiO-induced hydrogen spillover contributes to low H coverage over Pt, which effectively hinders over-hydrogenation of cyclohexanone and HER. We establish a scaling relationship between the intensity of hydrogen spillover and cyclohexanone selectivity by varying the types of anatase TiO, and show the universality of the strategy over other reducible metal oxides as the support (rutile TiO, CeO and WO). This work showcases an effective strategy for tuning hydrogenation selectivity in electro-catalysis, by taking advantage of thermo-catalytically well-documented hydrogen spillover effect.