Bimetallic Pd-Pt catalysts are used industrially to saturate aromatics in industrial feedstocks under mild reaction conditions to bypass the thermodynamic limitations. A considerable amount of research effort has been focused on elucidating the structural and electronic properties of bimetallic Pd-Pt particles, generally supported on acidic supports, to correlate their properties with their sulfur tolerance as well as with their catalytic activity/selectivity. However, the properties of bimetallic Pd-Pt particles under these characterization conditions are still partly unknown, particularly what happens during hydrotreating. We therefore prepared bimetallic Pd-Pt catalysts (Pd/Pt atomic ratio of 4/1) using the same precursors of noble metals and various supports, such as acidic and non-acidic ultra-stable Y-type (USY) zeolites, SiO2-Al2O3, SiO2 and Al2O3, and then investigated the structural and electronic properties of the supported bimetallic Pd-Pt particles. These properties that appeared under liquid-phase hydrotreating conditions were correlated with reaction selectivity for tetralin hydrogenation and in 4,6-dimethyldibenzothiophene hydrodesulfurization, as well as with Fourier-transform analyses of adsorbed CO, dispersion and EXAFS data of reduced/sulfided catalysts. The effects of several parameters involved - such as calcination/activation conditions and the presence of extra-framework alumina and chlorine in the zeolite supports - on the sulfur tolerance of the bimetallic Pd-Pt catalysts were also investigated. In addition to sulfur poisoning, agglomeration of the Pd-Pt particles and inhibitory effects caused by nitrogen-containing compounds and aromatics were also investigated to develop measures to minimize the agglomeration of Pd-Pt particles under hydrotreating conditions for real feedstocks. (C) 2007 Elsevier B.V. All rights reserved.