Investigation of the WO3/ZrO2 surface acidic properties for the aqueous hydrolysis of cellobiose

A series of WOx/ZrO2 with various tungsten oxide loadings (1-20) wt.% was prepared by co-precipitation. The catalysts were characterized by XRD, BET, XPS, Raman spectroscopy, TPR, ammonia adsorption microcalorimetry and pyridine FT-IR spectroscopy. XRD and Raman results showed that the ZrO2 support is predominantly present in the monoclinic phase when the WO3 loading was less than 5 wt.% and predominantly in the tetragonal phase above 10 wt.%. No formation of bulk WO3 was detected for the catalysts calcined at 700 C. which is also the case for the highest loaded samples. TPR results revealed that isolated WO3 species are easier to reduce than amorphous WOx. The ammonia adsorption microcalorimetric study evidenced acid sites with adsorption heats in the range 90<130 kJ.mo1(-1), in amounts which increase with increasing WO3 loading until reaching the monolayer. Concerning the acid site nature, a progressive increase of the amount of Bronsted sites with the WO3 loading was observed. The catalytic reaction of cellobiose disaccharide hydrolysis showed a better catalytic performance on the highest WO3 loaded catalysts, associated to the presence of Zr-stabilized WOx clusters and a strong protonic acidity. (C) 2011 Elsevier B.V. All rights reserved.