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Palladium, platinum and PdPt bimetallic colloidal particles were prepared in atomic ratios of 4:1, 1:1 and 1:4 by the reduction of K 2 PdCl 4 and/or K 2 PtCl 4 in the presence of cationic surfactant, tetradecyltrimethylammonium bromide (C 14 TABr). The nanoparticles in the "as prepared" state were characterized by TEM, EDS and XPS, UPS, permitting to determine their mean particle size, bulk and surface composition. The bulk composition of the bimetallic samples determined by EDS was close to their nominal value, while XPS indicated Pt enrichment near to the surface. All samples in the "as received" state contained surface oxide impurity and contained carbon impurities. The monometallic samples contained considerably more C as the bimetallic ones. A quasi-in situ H 2 treatment at 473 K in the electron spectrometer resulted in cleaner metals, containing less carbon and oxygen, as shown by XPS and UPS.

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Rh was deposited on a parent platinum black catalyst by an underpotential deposition method. Mean particle size and bulk composition of this Rh-Pt sample was determined by TEM and EDS. No individual Rh grains could be observed, but Rh was present in the near-surface regions, according to energy-filtered TEM images. The surface-sensitive cyclic voltammetry indicated 15-20% Rh on the surface. XPS, in turn, detected ∼ 2-2.5% Rh in the information depth. The Rh-Pt catalyst was tested in methylcyclopentane hydrogenative ring-opening reaction between 468 and 603 K and 8 to 64 kPa H 2 pressure (with 1.3 kPa MCP). The parent Pt black as well as a Rh black catalyst was also studied for comparison. MCP produced ring opening and hydrogenolysis products. The ring-opening products (ROP) consisted of 2-and 3-methylpentane (2MP and 3MP) as well as hexane (nH). These were the main products, together with some fragments and unsaturated hydrocarbons. The amount of the latter class increased at higher temperatures. The selectivities of ROP, fragments, and benzene over Rh-Pt catalyst as a function of temperature were between the values observed on Pt and Rh. The hydrogen pressure dependence of selectivities on Rh-Pt was more similar to that observed on Pt. Four subsequent treatments with O 2 and H 2 up to T = 673 K were applied on the bimetallic catalyst, followed by XPS and catalytic runs, respectively. These treatments promoted structural rearrangement, with XPS detecting less Rh in the near-surface region, partly as oxidized Rh after O 2 treatment. The catalytic behavior became more Pt-like on these structural and composition changes. We concluded that adding a relatively small amount of Rh to Pt creates bimetallic active sites with properties different from those of its components, behaving as a true bimetallic catalyst.

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