Bimetallic single atom promoted alpha-MnO2 for enhanced catalytic oxidation of 5-hydroxymethylfurfural

We report a synergetic dual-metal single-atom (Pd and Ni) promoting approach that modulates the catalytic activity and selectivity of alpha-MnO2 toward HMF oxidation. Pd and Ni have different spatial doping profiles and catalytic functions. Pd single atoms are embedded in the crystalline lattice of alpha-MnO2, which activates lattice oxygen and creates abundant oxygen vacancies. Ni single atoms that are mainly anchored on the surface of alpha-MnO2 improve the ability to dissociate molecular oxygen for healing oxygen vacancies. Pd and Ni work synergistically to accelerate the consumption and recovery of active lattice oxygen during HMF oxidation, which results in 3 fold enhancement of productivity and near-unity DFF selectivity. Ex situ and in situ characterization together with theoretical calculations confirm the pronounced effects of Pd and Ni on oxygen species. Compared to conventional single atom catalysts requiring a metal loading of 1-10 wt%, a single atom promoter requiring a tiny metal loading <0.5 wt% allows one to significantly improve the activity of alpha-MnO2.