Aluminium oxide-silica/carbon composites from rice husk as a bi-functional heterogeneous catalyst for the one-pot sequential reaction in the conversion of glucose

A simple preparation of aluminium oxide-grafted silica/carbon composites (Al-SiO2/C) from rice husk is reported. This composite has been employed as a bifunctional heterogeneous Lewis-Brønsted acid catalyst in the conversion of glucose into 5-hydroxymethylfurfural (HMF). SEM images showed the presence of bulk and nanosized Al-SiO2/C particles which were closely packed on the catalyst's surface. XPS data proved the presence of Al in the form of aluminium oxide and graphitic carbon with several functional groups. The XRD data confirmed this catalyst was amorphous. The results from N2 adsorption-desorption isotherm showed Al grafting did not affect its physicochemical properties. Pyridine-probe FTIR verified the existence of Lewis and Brønsted acid sites. A yield of 52% 5-hydroxymethylfurfural (HMF) was obtained at 170 °C in N-methylpyrrolidone (NMP) solvent. The catalyst proved to be stable without significant loss of yield after several recycling experiments.