Catalysts used to remove sulfur from petroleum cuts are mainly based on molybdenum disulfides dispersed on alumina carrier with cobalt or nickel atoms decorating the edges of the molybdenum disulfides slabs. In this study, we proposed a novel synthesis route for these materials assisted by supercritical carbon dioxide (scCO(2)), with the aim to disperse molybdenum and cobalt onto alumina support. This article describes a method to follow the preparation of these catalyst precursors, via the use of in situ Raman spectroscopy. This enables the monitoring of the evolution of the oxometallic species present on the surface of the support as a function of the preparation conditions. Raman spectra recorded as a function of temperature during the synthesis and ex situ X-Ray diffraction characterizations put in evidence that the use of scCO(2) to disperse active phases on the Al2O3 support led to different species compared to a conventional drying.