Catalytic conversion of sugarcane bagasse, rice husk and corncob in the presence of TiO2, ZrO2 and mixed-oxide TiO2–ZrO2 under hot compressed water (HCW) condition

The simultaneous hydrolysis/dehydration reaction of sugarcane bagasse, rice husk and corncob was studied under hot compressed water in the presence of TiO2, ZrO2 and TiO2–ZrO2 at 473–673 K. Among them, the reaction of corncob at 573 K in the presence of TiO2–ZrO2 produced the highest furfural and 5-hydroxymethylfurfural (HMF) yields (10.3% and 8.6%) with less by-products (i.e. glucose, fructose, xylose, and 1,6-anhydroglucose) selectivities. It was found that the catalyst preparation procedure and calcination temperature strongly affected its reactivity. Catalysts prepared by (co-) precipitation method gained higher reactivity than those prepared by sol–gel and physical mixing methods. The suitable calcination temperature for TiO2 and ZrO2 was at 773 K, whereas that for TiO2–ZrO2 was at 873 K; the XRD patterns revealed that different portions of phase formation were observed over catalysts with different calcination temperature. The portion of these phase formations affected the acidity–basicity of catalyst and thus the catalyst reactivity.