Preparation, physical characterization and catalytic properties of unsupported Pt–Rh catalyst

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 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.

Preparation, characterization and catalytic testing of GePt catalysts

“…H 2 reduced most Ge even at 300 K. GeO 2 also appeared, presumably as a result of reaction of Ge and oxygen chemisorbed over Pt during storage in air [19]. The Pt 4f peaks in the "as is" state and after H 2 treatments appeared at the same binding energy, corresponding to Pt 0 (Figure 2b), indicating a clean metallic state with no Pt-O interaction, not even with "chemisorbed oxygen" (E ~ 0.8 eV [19]), unlike to what was reported for PtRh [15]). …”

“…The second metal, Ge was deposited on both parent platinum catalysts via the ionization of pre-adsorbed hydrogen (a method based on the underpotential deposition of metals on foreign metal surfaces) [12,15,16]. 0.1 g of Pt catalyst, covered with adsorbed hydrogen was modified with Ge by exchanging the 1 mol L -1 HCl supporting electrolyte in the reactor with the same volume of deoxygenated 1 M HCl stock solution saturated with GeO 2 .…”

“…The present study deals with two Ge-Pt catalysts prepared with underpotential deposition of Ge [12], like in the case of Pt-Rh catalysts [15,16]. These catalysts were characterized by cyclic voltammetry, electron spectroscopy and electron microscopy, as well as test reactions of hexane and methylcyclopentane.…”

Ring Opening of Decalin Over Zeolite-Supported Iridium Catalysts

“…The fact that decalin conversion decreases with increasing hydrogen pressure is also a Fig. 3 The effect of reaction temperature and pressure on decalin conversion over Ir/H-Beta-ALD strong indication that hardly any direct ring-opening takes place, as the turn-over frequency of ring opening by metal catalyzed hydrogenolysis exhibits positive H 2 pressure dependencies [25,26]. The reaction products of decalin conversion over metalmodified zeolites can be classified, in agreement with the previous studies [6,7], into four main groups: skeletal isomers of decalin (i.e.…”

Catalytic Hydrogenation of Hydrocarbons for Gasoline Production

“…Meanwhile, literature showed that Ir catalysts have high activity and selectivity toward ring opening of C5 and C6 monocyclic molecules, but several reports show that C6 ring opening of molecule is enhanced by the use of bifunctional catalyst. 55,[58][59][60][61][62][63][64][65] This also followed the mechanism of the C6 to C5 contradiction on the acid site and the openings of the C5 ring on the metal site. 55 Ring opening of naphthenic molecule had been reported to occur via three distinct processes:…”