Enhanced glucose-to-5-hydroxymethylfurfural transformation activity over CePO4 catalyst: Insights into crystal structure, acidic property and reaction pathway

Abstract

The conversion of carbohydrates to high value-added 5-hydroxymethylfurfural (5-HMF) has aroused intensive research interest. Herein, a series of cerium phosphates was prepared by simple calcination accompanied by a hexagonal-monoclinic phase transformation. Hexagonal CePO₄-200 exhibits superior catalytic activity for the conversion of glucose to 5-HMF with a yield of 73 % compared with monoclinic CePO₄-800. The related characterization results confirm that hexagonal CePO₄-200 possesses unoccupied and open spaces leading to favorable coordination environments, good pore structure and high acid density, which contributed to activation and catalysis of glucose. Density functional theory (DFT) calculations proves that the hexagonal CePO₄-200 interface possesses a more effective charge transfer ability by comparing with monoclinic CePO₄-800 interface in Lewis acidic Ce³⁺ sites region thus enhancing the catalytic activity. Additionally, a feasible tandem reaction mechanism through glucose-to-fructose isomerization driven by Ce³⁺ acidic sites and fructose dehydration to 5-HMF catalyzed by P-OH group was proposed.