Simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions over RuS2/SBA and the effect of feed composition and the presence of Pt or Ir in the catalyst formulation have been studied. Activity tests were carried out in a flow reactor under a hydrogen pressure of 3.0 MPa and WHSV 32h(-1). The catalysts were characterized by X-ray diffraction (XRD), N-2 adsorption desorption isotherms at -196 degrees C, CO chemisorption, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy of adsorbed CO at low temperature. Characterization results reveal that under the presence of noble metals the dispersion of the RuS2 phase is not affected, the RuS2 coordinatively unsaturated sites (CUS) are in a very sulfided ambient and their population increases; while the noble metals are poorly sulfided and undergo reduction upon reaction. The evaluation of HDN and HDS activity for RuS2/SBA when both (dibenzothiophene) DBT and (quinoline) Q were present in the feed has highlighted the high activity of the RuS2 phase in hydrotreating. The HDS reaction is hardly affected by the presence of Q molecules, with only the hydrogenation (HYD) sites responsible for cyclohexylbenzene (CHB) formation being anyhow altered. HDN results improve in the presence of DBT, even showing high HDN conversion when Q is present in great quantities. These catalytic results strongly suggest that the HDN and HDS reactions must take place on different sites. CO-FTIR spectroscopy results have evidenced that N-containing molecules block the CUS sites responsible for CO adsorption although when S-containing molecules are present, N-containing molecules should be easily transformed since CO-adsorption sites are again available. The addition of small quantities of iridium and platinum to ruthenium sulfide improves the catalytic behavior of the RuS2 catalyst. This is probably due to the greater number of CUS sites and Ir and Pt acting as active hydrogen suppliers. Moreover, these noble metals can act as real active sites where the DBT HDS reaction takes place. (C) 2013 Elsevier Inc. All rights reserved.