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

Coordination polymers are closely correlated with porous and robust structures. In this work, a variety of novel coordination organophosphate-Hf polymers functionalized with Bronsted/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 Bronsted (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 m(2) g(-1)), large pore volume (0.24 cm(3) 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 gamma-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.