The benefit of TiO2, ZrO2 and SO4-ZrO2 on the reactions of C-5-sugar (xylose), C-6-sugar (glucose), cellulose, and lignocellulose was studied in hot compressed water (HCW) at 473-673 K with an aim to produce furfural and 5-hydroxymethylfurfural (HMF). TiO2 and SO4-ZrO2 were found to active for hydrolysis and dehydration reactions producing high furfural and HMF yields with less by-products (i.e. glucose, fructose, xylose, and 1,6-anhydroglucose (AHG)) formation, whereas ZrO2 was highly active for isomerization reaction; thus significant amount of fructose was observed in the liquid product. Importantly, it was also found that the starting salt precursor, the sulfur-doping content (for SO4-ZrO2) and the calcination temperature strongly affected the catalyst reactivity. Catalysts prepared from the chloride-based precursors (i.e. ZrOCl2 and TiCl4) gained higher reactivity compared to those prepared from nitrate-based precursors (i.e. ZrO(NO3)(2) and TiO(NO3)(2)) due to their greater acidity, according to the NH3- and CO2-TPD studies. For SO4-ZrO2, among the catalyst with sulfur contents of 0.75%, 1.8% and 2.5%, SO4-ZrO2 with 1.8% sulfur content presented the highest acidity and reactivity toward hydrolysis and dehydration reactions. It is noted that the suitable calcination temperature for all catalysts was at 773 K; the XRD patterns revealed that different portions of phase formation was observed over catalysts with different calcination temperatures i.e. anatase/ rutile for TiO2 and monoclinic/tetragonal for ZrO2 and SO4-ZrO2; the portion of these phase formations obviously affected the acidity-basicity of catalyst and thus the catalyst reactivity. (C) 2010 Elsevier Ltd. All rights reserved.