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Electrosorption of rhodium on a polycrystalline platinum surface has been studied. It has been found that a complete Rh-coverage can be obtained by spontaneous adsorption via the ionization of preadsorbed hydrogen. Underpotential deposition of rhodium has been observed both in 0.5 M H2SO4 and 0.2 M HCl supporting electrolytes. The value of the underpotential shift was found to be about 100–120 mV. [Copyright &y& Elsevier]

The adsorption of cinchonidine (CD) on polycrystalline platinum surfaces in 0.5 mol dm−3 H2SO4 has been investigated. It has been found that adsorption is irreversible, desorption takes place at relatively high potentials simultaneously with the oxidation of CD molecules. According to our results CD covers only a part of the Pt surface and maximal coverage is influenced by the surface structure. Some assumptions for the site requirement of an adsorbed CD molecule have also been made. [Copyright &y& Elsevier]

Abstract: 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 H2 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 O2 and H2 up to 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 O2 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. [Copyright &y& Elsevier]