Titanium hydrogenphosphate: An efficient dual acidic catalyst for 5-hydroxymethylfurfural (HMF) production

Abstract

Dual Brønsted and Lewis acidity of solid acid catalysts enhances selective production of 5-hydroxymethylfurfural (HMF). This report describes a simple template-free synthetic approach for the preparation of titanium hydrogenphosphate (TiHP) material containing Lewis and Brønsted acid sites. As-synthesized material has been thoroughly analyzed by several analytical methods for elucidating its structural properties, including determination of the presence of Brønsted acidic phosphate group and measurement of total acid density. NH3-TPD data reveals high surface acidity (1.43 mmol g-1) of the TiHP, which is indeed reflects to its catalytic effectiveness for the conversion of fructose, giving 55% HMF in biphasic solvent. Glucose conversion gives better yield (35%) when the reaction was carried out in a larger reactor (2L Parr reactor), which might be due to better mechanical stirring and hence higher mixing efficiency of the reactants. Brønsted acid sites in the catalyst facilitated the formation of furan ring opening product, levulinic acid, at higher temperatures. The catalyst shows excellent recyclability and the recovered catalyst after the 3rd cycles retained XRD and TGA characteristics.