One-step catalytic upgrading of bio-based furfural to γ-valerolactone actuated by coordination organophosphate–Hf polymers

Abstract

Coordination polymers are closely correlated with porous and robust structures. In this work, a variety of novel coordination organophosphate–Hf polymers functionalized with Brønsted/Lewis acid and base sites were prepared from vinylphosphonic acid (VPA), p-toluenesulfonic acid (p-TSA), and HfCl₄ using a one-pot solvothermal approach. The strength and content of Lewis (L) and Brønsted (B) acid species can be regulated by adjusting the molar ratio of VPA, p-TSA, and HfCl₄. Specifically, VPA–Hf(1 : 1.5)-0.5 possessed spherical porous structure, a pore size of 3.3 nm, high surface area (290 m² g⁻¹), large pore volume (0.24 cm³ g⁻¹), and enhanced acid density (2.5 mmol g⁻¹) with an appropriate L/B acid ratio of 5.3 and was found to exhibit superior performance in the one-step conversion of furfural (FF) to γ-valerolactone (GVL) in a high yield of 81.0%, with a turnover frequency of 5.0 h⁻¹. The VPA–Hf(1 : 1.5)-0.5 catalyst could be recycled at least four times with steady catalytic activity. The relatively lower activation energy (Ea = 58.8 kJ mol⁻¹) and E-factor value (0.19) demonstrate the high efficiency and eco-friendliness of the conversion process mediated by VPA–Hf(1 : 1.5)-0.5. Moreover, a plausible mechanism for producing GVL from FF via cascade reaction steps in a single pot was proposed, where L/B acid sites over VPA–Hf(1 : 1.5)-0.5 play synergistic and concerted roles.