Complete Aqueous Hydrogenation of 5-Hydroxymethylfurfural at Room Temperature over Bimetallic RuPd/Graphene Catalyst

Aqueous hydrogenation of 5-hydroxymethylfurfural (HMF) was performed over the RuPd/graphene (RGO) bimetallic catalyst at room temperature (20 °C). The combination of Pd and Ru gave the best catalytic performance for the complete hydrogenation of HMF to 2,5-dihydroxymethyltetrahydrofuran (DHMTHF) compared with the corresponding monometallic Ru/RGO and Pd/RGO catalysts. The yield of DHMTHF reached 92.9% over the RuPd/RGO catalyst, while it was 6.0% and 4.1% over the monometallic Ru/RGO and Pd/RGO catalyst, respectively. High-resolution TEM (HRTEM), high-angle annular dark-field STEM (HAADF-STEM), and H2-TPR identified the formation of RuPd alloy in RuPd/RGO catalyst. The strong interaction between Ru and Pd caused the formation of Ruδ−–Pdδ+ pairs, as made evident by XPS. The DFT calculations revealed that the electron feedback was from the furan ring of HMF and the intermediate product 2,5-dihydroxymethylfuran (DHMF) to the electron-deficient Pdδ+ species in Ruδ−–Pdδ+ pairs. Accordingly, the high efficiency of RuPd/RGO catalyst in the hydrogenation of HMF to DHMTHF results from the electron transfer circle between the Ruδ−–Pdδ+ pairs and HMF molecules, i.e., the electron transfer from Ruδ− to the C═O group of HMF and the electron feedback from the C═C bond in the furan ring of HMF to the electron-deficient Pdδ+ species in Ruδ−–Pdδ+ pairs.