The conversion of guaiacol, a lignin model compound, over SiO2-supported Re metal, oxide and sulfide catalysts in a batch reactor at 300 degrees C and 5 MPa of hydrogen pressure were studied. The oxide catalyst was prepared by wet impregnation with a loading of 2.5 atom of Re per nm(2) of support. The sulfide and metal catalysts were prepared by sulfidation and reduction, respectively, of the Re oxide catalyst. The catalysts were characterized by N-2 adsorption, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and transmission electron microscopy (TEM). Catalytic activity was correlated with XPS analysis of the post-reaction catalysts. The ReOx/SiO2 catalyst was the most active and selective towards deoxygenated products, and this was attributed to increase in the concentration of metal oxide defect sites (due to in situ partial reduction of the oxide catalyst during the reaction). This result reveals the high potential of ReOx/SiO2 catalyst for bio-oil upgrading because it shows, among other things, that it is unnecessary to add undesirable sulfiding agent to maintain catalytic activity. (C) 2014 Elsevier B.V. All rights reserved.