Photocatalytic intermolecular hydrogen transfer in hydrogenative cyclization of levulinic acid to γ-valerolactone over single-atom Pt/GFs

The hydrogenative cyclization of levulinic acid (LA) to γ-valerolactone(GVL) is a key reaction in the valorization of carbohydrates to renewable fuels and chemicals. Herein, the novel Pt single atoms (Pt SA) photocatalyst supported an the 3D ordered pores graphene framework (GFs) has been successfully synthesized via in-situ photo-reduction process. The structure of Pt SA/GFs are well investigated by various characterization techniques, including aberration-corrected scanning transmission electron microscopy, high-energy X-ray diffraction, X-ray photo-electron spectroscopy, and X-ray absorption fine structure. It is found that the Pt SA/GFs are active toward aqueous levulinic acid (LA) hydrogenation to γ-valerolactone. The as-fabricated catalyst with 2 % Pt loading affords an excellent LA hydrogenation performance, achieving a GVL yield as high as 85.23 % at normal temperature and pressure, which is superior to most of the reported Pt-based catalysts. Moreover, this catalyst demonstrates excellent stability and reusability up to 5 cycles. The experimental investigation and density functional theory (DFT) calculations reveal that the optimal coordination Pt-C2O2 has a stronger electron-transfer ability and a lower Gibbs free energy difference (ΔG), reducing the activation energy of the hydrogenation of LA to 4-hydroxyvalerate (HPA), which is the rate-determining step. Meanwhile, the catalyst was able to reduce the activation energy of the dehydration of HPA to GVL, a key intermediate step for LA hydrogenation. This work provides an effective method for the synthesis of single-atomic metal catalysts, and this hydrogenation-dehydrogenation coupling process also provides insight into the development of Pt-based catalysts for biomass conversion. It holds promise for the integration of photocatalysis into renewable energy systems, contributing to the sustainable of biofuel production.