Synthesis of hierarchically porous tantalum phosphate catalysts by a sol–gel method for transformation of glucose to 5-hydroxymethylfurfural

Abstract

A hierarchically porous and highly effective tantalum phosphate (TaP) solid acidic catalyst was synthesized using a sol–gel method accompanied by phase separation for converting glucose to 5-hydroxymethylfurfural (HMF). The TaP sample formed the TaPO₅ phase after calcining at 600 °C (TaP-600) for 4 hours with a surface area of ca. 103 m² g⁻¹ and an acidity of ca. 0.18 mmol_NH3 g⁻¹. The TaP-600 sample had a co-continuous macroporous structure with a regular and orderly pore arrangement, which was conducive to the diffusion of reactants and products, thereby reducing side reactions. The TaP-600 sample can afford an HMF yield of 25.6% by treating with 1.0 wt% glucose at 170 °C in pure water. Using a water–DMSO homogeneous system or a water/MIBK biphasic reaction system can protect HMF from further decomposition, obtaining a HMF yield of 63.8% and 67.1% (mol mol⁻¹), respectively. The TaP-600 sample also showed high catalytic performance at high glucose concentration in the water/MIBK system, e.g. the HMF yields reached 27.5% and 23.7% at glucose concentrations of 15.0 wt% and 20.0 wt%, respectively. The productivity of HMF reached 6.6 × 10⁻² mol h⁻¹ kg_solution⁻¹ at an initial glucose concentration of 20.0 wt% in the water/MIBK biphasic system with a catalyst loading (weight ratio of catalyst to glucose) of 10.0 wt%. The TaP-600 sample can retain most of its activity after three catalytic cycles giving an HMF yield of 17.9%. These results demonstrate the significant potential of TaP for industrial-scale HMF production.