Trade-Off between Acidic Sites and Crystallinity of the WO3-TiO2 Catalyst toward Dehydration of Glucose to 5-Hydroxymethylfurfural

The dehydration of glucose to 5-hydroxymethylfurfural (HMF) is one of the most coveted catalytic reactions from energy and environmental perspective. In spite of the exhaustive work, the understanding of the reaction mechanism is still debated in literatures. Here, the composite WO3-TiO2 catalyst was synthesized by different routes such as solution combustion synthesis method and microwave-assisted hydrothermal method for the glucose dehydration reaction. The synthesized materials were structurally characterized by X-ray diffraction, Raman spectroscopy, and UV vis diffuse reflectance spectroscopy. The surface morphology was studied with field emission scanning electron microscope and surface area analysis. The surface acidity and total acidic site strength of the synthesized materials were revealed by pyridine Fourier transform infrared spectra and temperature-programmed desorption of ammonia. The results showed that the solution combustion-synthesized materials upon calcination become more crystalline, however loose the surface acidity. In addition, the surface acidity was found to be directly proportional to the catalytic activity of the materials. The microwave-synthesized as-prepared composite WO3-TiO2 showed highest surface acidity as well as highest glucose conversion with HMF yield. The findings were compared with the existing values in the literature, and the dual site reaction mechanism was proposed for the glucose dehydration reaction.