Silica-supported trimetallic catalysts containing Pt, Sri and a group 13 metal (PtSnM, M = Ga, In, Tl) were prepared by consecutive impregnation steps from cis-[PtCl2(PPh3)(2)] and chloride precursors. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffraction (ED) and energy dispersive X-ray analysis (EDX) showed large platelet-like particles of PtSn1-xMx phases. PtSnGa catalyst with a Pt/(Sn + Ga) molar ratio of 1.72 showed a bimodal particle distribution and a Pt phase was identified. Differences in surface structures were also revealed by the performance of catalysts in the dehydrogenation of n-hexane. For PtSnIn and PtSnTl (Pt/(Sn + M) molar ratio of about 1) the dehydrogenation was favoured. In contrast, PtSnGa catalyst yielded hydrogenolysis products. Photoelectron spectra showed the Pt 4f(7/2) level at a binding energy of 170.0-71.8 eV in all cases. Moreover, the FF-IR spectra of chemisorbed CO on the PtSnGa showed a slight shift in the v(CO) toward higher values with respect to the monometallic catalyst, pointing to an electronic effect in accordance with photoelectron spectroscopy. (C) 2003 Elsevier Science B.V. All rights reserved.