This paper compares the catalytic behavior of several heterogeneous acid catalysts in the direct hydrolysis of an untreated softwood dust. Among the various catalysts investigated, some were characterized by a relatively high yield to monosaccharides, such as a Zirconium phosphate and the reference Amberlyst 15. Conversely, some catalyst types, i.e. Sn/W mixed oxide and Zirconia-grafted trifluoromethanesulfonic acid, were selective into glucose, since sugars derived from hemicellulose dissolution and hydrolysis were rapidly degraded. A detailed analysis of the reactivity of Zr/P/O was conducted, in the hydrolysis of both untreated and ball-milled microcrystalline cellulose; at 150 degrees C and 3 h reaction time, the catalyst gave high selectivity to glucose, with negligible formation of 5-hydroxymethylfurfural, and moderate cellulose conversion. After cellulose ball-milling, a notable increase in conversion was achieved, still with a high selectivity to glucose and very low formation of degradation compounds. The catalyst showed high affinity for beta-1,4-glucans, as demonstrated by the activity in cellobiose hydrolysis into glucose. (C) 2013 Elsevier B.V. All rights reserved.