The sulfidation of supported NiW hydrotreating catalysts is followed by a combination of X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), Raman and electron paramagnetic resonance (EPR) spectroscopy. In this work, we compared two catalysts prepared by incipient wetness impregnation from different precursors. The first one is an innovating catalyst prepared with the nickel salt of the derived lacunary Keggin heteropolyanion (HPA) Ni4SiW11O39 and the second one is a conventional catalyst synthesized from ammonium metatungstate and nickel nitrate. The results show for both catalysts that the sulfidation of nickel and tungsten elements does not occur at the same temperature. However, a better sulfidation of tungsten and nickel atoms respectively to WS2 and NiWS phases is observed at 400 degrees C for HPA precursor compared to conventional catalyst, highlighting the benefit of HPA starting material. (c) 2012 Elsevier B.V. All rights reserved.