The influence of the W/Ni ratio and the phosphorous content as a promoter in the catalytic performance of NiW Sulfide supported on zirconium containing mesoporous silica in the hydroconversion of tetralin has been studied. Three catalysts with a W loading of 20 wt.% and Ni loading of 2.5. 5 and 7.5 wt.% were prepared. To study the effect of phosphorous as promoter, prior to the metallic impregnation, 0.5, 1.5, 3.0 and 5.0 wt.% Of P2O5 was incorporated to the support. The catalysts were sulfided with a H-2/H2S mixture at 400degreesC for 2 h, and finally tested in the hydrogenation (HYD)/ring-opening of tetralin at 6.0 MPa (4.5 MPa H-2 and 1.5 MPa N-2). Using IR and XP spectroscopies, a correlation has been established between the catalytic performance and the dispersion and type of compounds formed on the support. The formation of a highly dispersed NiWO4 phase, easily sulfidable, and the high acidity of mild strength of the catalysts, could explain the good catalytic performance observed. The catalyst with 5 wt.% of Ni, 20 wt.% of W and 0.5 wt.% Of P2O5 shows an excellent catalytic performance and is higher than that observed with a sulfided commercial Ni-Mo/Al2O3, in the same experimental conditions. (C) 2003 Elsevier B.V. All rights reserved.