The direct hydrolysis of cellulose to glucose, HMF and other soluble by-products at 190 degrees C in water solution using zeolites (H-BEA, H-MOR), sulphated zirconia supported over mesoporous silica (SBA-15), Amberlyst (R) 15, heteropolyacids and AlCl3 center dot 6H(2)O as acid catalysts was studied using a high cellulose to catalyst ratio (10), not-pretreated (neither mechanically nor chemically) cellulose and a static (not mixed) autoclave. Under these conditions, not usually considered, but relevant for industrial applications, micro and mesoporous solid acid catalysts are active in the direct hydrolysis of cellulose to glucose, HMF and other soluble by-products. The reactivity in crystalline cellulose conversion is determined on one side from the need to realize an efficient solid-solid interaction between the external surface of the catalyst and the crystalline cellulose, and on the other side on the need to limit the secondary reactions of the formed products. Microporous materials, due to the presence of shape-selectivity effects limiting the polymerization of glucose to humic-type species show the highest formation of glucose and HMF with respect to the sulphated zirconia supported over mesoporous silica (SBA-15) and homogeneous heteropoly acids. (C) 2011 Elsevier B.V. All rights reserved.