Effect of Calcination Temperature on the Acidity of Manganese Orthophosphate Catalyst for the Glucose Conversion to 5-Hydroxymethylfurfural (HMF)

Manganese orthophosphate (Mn3(PO4)2) catalyst was successfully synthesized by a simple, fast, and cost-effective method using precipitation at room temperature. The precipitates obtained were calcined at various temperatures (350, 600, and 800 °C) were studied. The structure of the three synthesized crystals was characterized by X-ray powder diffraction (XRD), chemical bonds were observed by Fourier Transform Infrared (FTIR) spectroscopy, and the acidity of the catalyst was determined by the pyridine adsorption-FTIR method. The characterization results showed the formation of manganese orthophosphate which had an amorphous phase at 350 °C and a monoclinic crystalline phase at 600 and 800 °C. The highest Lewis and Brønsted acid sites of the manganese orthophosphate catalyst (350°C). The catalytic test of all manganese orthophosphate catalysts was carried out in the conversion reaction of glucose to 5-Hydroxymethylfurfural (HMF). The results of the catalysis test showed that the highest glucose conversion 88.54% was achieved by a catalyst with the highest Brønsted acid site and the highest 5-HMF yield 60.87% was obtained from manganese orthophosphate (350 °C) catalyst. The formation of 5-HMF from cellulose is influenced by the acidity of the catalyst, especially Brønsted acid.