Direct Transformation of Bio-Based Furfural into γ-Valerolactone over SO₃H-Functionalized P─O─Hf Hybrid Catalysts

γ-Valerolactone (GVL) has great application potential in organic synthesis and biofuels, while its high-efficiency production from easily available bio-based feedstock is challenging. In this work, SO₃H-functionalized P-O-Hf hybrid catalysts GPCS-Hf(n:m) were facilely prepared by solvothermal treatment of glucose-containing organic precursors (GPC) and Hf⁴⁺ in a mass ratio of n:m. The acid strength and Lewis/Brønsted acid sites of GPCS-Hf(n:m) could be modulated by tuning the GPC/Hf⁴⁺ ratio. Among them, GPCS-Hf(1:1.5) with appropriate acid-base properties delivered prominent catalytic activity in the direct upgrading of a bio-based bulk chemical furfural (FF) to GVL with a good yield of 71%, as optimized by response surface methodology. Especially, the suitable distribution of Lewis acid (Hf⁴⁺), Lewis base (O^2-), and Brønsted acid (H⁺) sites played a synergistic role in cascade transfer hydrogenation, furan ring opening, second hydrogenation, and lactonization. Moreover, the GPCS-Hf(1:1.5) catalyst was unveiled to have a uniform elemental dispersion, relatively large specific surface area, and amorphous structure, which might also contribute to its superior efficiency. Recycling experiments showed that GPCS-Hf(1:1.5) could be reused at least six times with almost no decline in activity. The overall bio-derived catalytic conversion system offers a more sustainable manner for biomass valorization.