Process for the preparation of a catalyst based on molybdenum for use in hydrotreatment or in hydrocracking

A process for the preparation of a catalyst comprising at least one support, optionally at least one metal from group VIII of the periodic classification of the elements and at least molybdenum, said process comprising:

• introducing the molybdenum onto the support, in an organic solvent A, in the form of at least one mononuclear precursor compound based on Mo, in its monomeric or dimeric form, having at least one Mo═O or Mo—OR bond or at least one Mo═S or Mo—SR bond where:
• R=CxHy where x≧1 and (x−1)≦y≦(2x+1) or R=Si(OR′)3 or R=Si(R′)3 and where R′=Cx′Hy′where x′≧1 and (x′−1)≦y′≦(2x′+1);
• to obtain an impregnated support,
• drying the impregnated support under vacuum and at ambient temperature to obtain a dried impregnated support, and
• conducting ex situ sulphurization of the dried impregnated support in a H2S/H2 or H2S/N2 mixture containing at least 5% by volume of H2S in the mixture at a temperature between 300 and 400° C.