Silica-supported MoP catalysts were prepared by temperature-programmed reduction (H-2-TPR) at 550, 600 and 700 degrees C of the corresponding dried or calcined substrates. Two catalysts were prepared by using two different synthetic approaches. A MoP catalyst was prepared using the method described in the literature that uses ammonium phosphate (NH4H2PO4) and ammonium heptamolybdate ((NH4)(6)Mo7O24 center dot 4H(2)O) precursors, calcination and subsequent H-2-TPR at high temperature. A new synthetic approach was carried out to prepare another MoP catalyst using ammonium molybdate ((NH4)(2)MoO4) and phosphorous acid (H2PO3H) as precursors and subsequent H-2-TPR. The catalytic activity was evaluated in the individual and simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions performed in a flow reactor under a hydrogen pressure of 3.0 MPa. The fresh reduced and spent catalysts were characterized by ICP, N-2 adsorption-desorption isotherms at -196 degrees C, XRD, HRTEM, NH3-TPD, XPS and elemental chemical CNHS analysis. The silica-supported MoP catalysts prepared by the new synthetic method were more active in the HDS of DBT than the catalyst prepared by reduction of calcined substrate. The catalyst characterization results showed that the lower reduction temperature required to form the MoP species is responsible for the enhancement in catalytic performance. The key factors influencing on the catalytic activity are: a large specific surface area, high acidity and good dispersion of MoP phase on the support substrate. Activity measurements in simultaneous HDN-HDS showed that quinoline conversion is enhanced in the presence of a small amount of DBT whereas the HDS of DBT reaction does not appear to be inhibited by a small amount of quinoline added to the feed. (C) 2011 Elsevier B.V. All rights reserved.