Carbon accumulation, deactivation and reactivation of Pt catalysts upon exposure to hydrocarbons

Paál, Z.; Wootsch, Attila; Schlögl, Robert; Wild, Ute

doi:10.1016/j.apcata.2004.12.027

Cited by 23 publications

(27 citation statements)

References 56 publications

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“…The results obtained with the SiO 2 supported Rh-Pt, focusing on its catalytic properties in methylcyclopentane (MCP) reactions, have been published previously [21]. The unsupported sample, the subject of the present work, can be studied more easily by several characterization methods, continuing our previous activity using unsupported metals [22][23][24]. Electron microscopy (EM), electrochemical [cyclic voltammetry (CV)] measurements, and electron spectroscopy (XPS) were used for physical characterization after various treatments of the unsupported Pt-Rh catalyst.…”

Section: Introductionmentioning

confidence: 52%

“…This effect is discussed in the next section. The low activation energy also can be related to the deactivation by coke formation at higher temperature [23,25]. However, the surface state under these conditions is reproducible, as confirmed earlier by repeated reactions on Pt black [25].…”

Section: Effects Of Reaction Temperaturementioning

confidence: 63%

“…Table 1 shows that treatments with H 2 at even at 300 K reduced the samples but were less effective in removing C impurities. O 2 , in turn, was efficient in removing C, as was also found for monometallic Pt [23,25,26]. The determination of a low percentage of Rh could not be very precise (due, e.g., to scattering points, background subtraction errors, etc., in lowintensity peaks).…”

Section: Xpsmentioning

confidence: 99%

“…The carbon impurity corresponded to the hardly removable "adventitious carbon" observed after most treatments on Pt black [23,26]. The C 1s peak (Fig.…”

Section: Xpsmentioning

confidence: 99%

“…A Leybold LHS 12 MCD instrument with a MgKα anode for XPS (pass energy, PE = 48 eV) was used, as reported earlier [23,29,30]. The binding energy (BE) was calibrated to the Au 4f 7/2 line (BE = 84.0 eV).…”

Section: Xpsmentioning

confidence: 99%

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

Paál

Győrffy

Wootsch

et al. 2007

Journal of Catalysis

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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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Section: Introductionmentioning

confidence: 52%

Section: Effects Of Reaction Temperaturementioning

confidence: 63%

Section: Xpsmentioning

confidence: 99%

“…The carbon impurity corresponded to the hardly removable "adventitious carbon" observed after most treatments on Pt black [23,26]. The C 1s peak (Fig.…”

Section: Xpsmentioning

confidence: 99%

Section: Xpsmentioning

confidence: 99%

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

Paál

Győrffy

Wootsch

et al. 2007

Journal of Catalysis

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Carbons

Schlögl

2008

Handbook of Heterogeneous Catalysis

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The element carbon plays a multiple role in heterogeneous catalysis. In homogeneous catalysis it occurs of course as the most prominent constituent of ligand systems and will be treated as such there. Carbon-containing molecules are, in most catalytic applications, the substrates of the process under consideration. Deposits and polymers of carbon often occur as poisons on catalysts. Carbon deposition is the most severe problem in certain zeolite applications. In hydrogenation reactions carbon deposits are thought to act as modifiers for the activity of the catalyst and to provide selectivity by controlling the hydrogenationdehydrogenation activity of the metal part of the catalyst. Carbon deposits are even thought to constitute part of the active sites in some cases. Carbon is a prominent catalyst support material as it allows the anchoring of metal particles on a substrate which does not exhibit solid acid-base properties. Carbon is finally a catalyst in its own right allowing the activation of oxygen and chlorine for selective oxidation, chlorination and de-chlorination reactions. These multiple roles of the element carbon are in parallel with a complex structural chemistry giving rise to families of chemically vastly different modifications of the element. It is a special characteristic of carbon chemistry that many of these modifications cannot be obtained as phase-pure materials. This limits the exact knowledge of physical and chemical properties to a few archetype modifications, namely graphite and diamond. The reason for this poor definition of materials is found in the process of its formation. This is comprised of difficult to control polymerisation reactions. Such reactions will occur also in catalytic reactions with small organic molecules. The nature of carbon deposits will therefore reflect all the complexity of the bulk carbon materials. It is one aim of this article to describe the structural and chemical complexity of "carbon" or "soot" in order to provide an understanding of the frequently observed complexity of the chemical reactivity (e.g. in re-activation processes aiming at an oxidative removal of deposits). The surface chemistry of carbon which determines its interfacial properties is a rich field as a wide variety of surface functional groups are known to exist on carbon. The by far most important family of surface functional groups are those involving oxygen. Other prominent heteroatoms on the surface are hydrogen and nitrogen. This article focusses on the description and characterisation of oxygen surface functional groups. In the final section, selected case studies of carbon chemistry in catalysis will be discussed in order to illustrate characteristic properties of carbon materials as wanted or unwanted components in catalytic systems. Regarding the literature on basic properties of carbon materials, the reader is referred to the extensive collection of review papers published in the series Chemistry and Physics of Carbon. Editors P.L.

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