Solids based on HY zeolite were modified by either dealuminization (D) followed by chemical vapour deposition of silicon (CVD). Additionally, impregnation of Pt or Ni was performed over selected D and CVD solids. Samples were characterized by XRD, Al-27 and Si-29 NMR, acidity measurements. N-2 adsorption/desorption isotherms, Raman analysis and evaluated in n-octane hydroconversion at P = 1 atm and T = 300 degrees C. In comparison with the CVD and pure D series of solids. Pt impregnation on dealuminated HY resulted in a high level of isomerization products. Although the conversion upon using Ni-containing dealuminated HY was elevated, cracking products were predominant over this solid. The trends in the activity can be explained by the accessibility of acidic sites and their acidity. The catalytic activity follows the order PtCVD1 > NiD > PtD similar to D > CVD1. The combined effect of moderate acidity and Pt dispersion resulted in better catalytic performance for the PtCVD1 catalyst, which was active in the hydroisomerizadon reaction (conversion of 30%) with almost no coking on the sample, whereas cracking products were predominant over other solids. The characterization of spent catalysts showed no loss in activity, with low coke deposition on solid surface over the CVD1 sample in comparison with the D series of solids. Furthermore, mechanistic insights demonstrated that on PtCVD1, the adsorbed carbon species were formed via the cracking and oligomerization of n-octane precursors. (C) 2011 Elsevier B.V. All rights reserved.