Platinum catalytic behaviour

The aim of this paper is to understand the influence of zinc on platinum catalytic behaviour. The added metal can either deactivate or provoke an increase in the catalytic activity of platinum either for reforming reactions or depollution reactions respectively, even when the gas atmosphere is always reductive. We shall study the influence -i) of the mode of preparation, -ii) of the zinc loading and -iii) of the kinetic parameters, on the activity of S-[Pt-Zn] catalysts in DeNOx reactions.The catalysts have been characterised by TPR, chemisorption and EXAFS and tested in the reaction of selective catalytic reduction (SCR) using diesel conditions. 

Collier, P. J., Iggo, J. A. and Whyman, R. 1999. Preparation and characterization of solvent-stabilised nanoparticulate platinum and palladium and their catalytic behaviour towards the enentioselective hydrogenation of ethyl pyruvate. Journal of Molecular Catalysis A-Chemical, 146 149-157. 

FIGURE 10.12 Nitrogen adsorption isotherms and corresponding pore size distributions of a typical FSP-derived powder and the commercial reference catalyst E4759. Note that the particles of the flame-made catalyst are virtually nonporous. The indicated macropores originate from interstitial voids of the agglomerated particles. (From Strobel, R., Stark, W.J., Madler, L., Pratsinis, S.E., and Baiker, A., Flame-made platinum/alumma structural properties and catalytic behaviour in enantioselective hydrogenation, J. Catal., 213, 296, 2003.)... 

Strobel, R., Stark, W.J., Madler, L., Pratsinis, S.E., and Baiker, A., Flame-made platinum/alumina structural properties and catalytic behaviour in enantioselective... 

Consistent with this model It has been shown on platinum (223) that the reaction occurs on the surface covered with a near monolayer of carbonaceous species In an apparently structure-insensitive loanner but that cyclohexene hydrogenation and dehydrogenation reactions proceed on the clean metal surface In a structure sensitive manner and in addition there Is then a striking variation In catalytic behaviour between various crystal surfaces ... 

Both nickel and platinum based catalysts are active for the C02-reforming reaction. The disadvantage of nickel based catalysts is their tendency to form coke and deactivate rapidly [6]. We have shown earlier that Pt/ZrOj is a stable (by virtue of low rate of coke formation) and active catalyst for CO2/CH4 reforming [8]. In this contribution we address the characteristics of Pt/Zr02 catalysts that influence its catalytic behaviour in order to be able understand the mechanism of the catalysed reaction and help in to optimising catalyst. 

The observed structure sensitivity of platinum in the decomposition reaction of NO is in accord with the known catalytic behaviour of the metal. While the stepped Pt(lll) surface adsorbs NO only in its molecular form,the stepped Pt(100) surface also decomposes NO. Although step sites are generally regarded as active in N-0 bond breaking we must conclude that this does not apply always. Banholzer et al.(ref.3) developed a model in order to explain the plane to plane variations... 

Boutonnet, M., Kizling, J., Touroude, R., Maire, G., Stenius, R Monodispersed colloidal metal particles from non-aqueous solutions catalytic behaviour for the hydrogenation of but-1-ene of platinum particles in solution. Appl. Catal. 20(15), 163-177 (1986)... 

It has been published that hydrophobic-activated carbons can be suitable supports for noble metal species active for total oxidation. The catalytic behaviour of platinum and palladium supported on carbon-based monoUths was studied in the low temperature catalytic combustion of benzene, toluene and m-xylene, and compared with the corresponding behaviour of Pt-supported on y-Al203 coated monoliths. Carbon-based monoliths showed much better catalytic performance, which was ascribed to the fact that the carbon surface is more hydrophobic than the y-Al203, and the poisoning effect of water molecules produced during the combustion was... 

J. Silvestre-Albero, J.C. Serrano-Ruiz, A. Sepulveda-Escribano, F. Rodriguez-Reinoso, Modification of the catalytic behaviour of platinum by zinc in crotonaldehyde hydrogenation and iso-butene dehydrogenation. Appl. Catal. A 292, 244—251 (2005)... 

Mass loss determinations refer to the total change resulting from reactant decomposition and usually include contributions from a mixture of product compounds, some of which would normally be condensed under conditions used for accumulatory pressure measurements. Such information concerned with the overall process is, however, often usefully supplemented by evolved gas analyses (EGA) using appropriate analytical methods. Sestak [130] has made a detailed investigation of the effects of size and shape of reactant container on decomposition kinetics and has recommended that the sample be spread as a thin layer on the surfaces of a multiple plate holder. The catalytic activity of platinum as a reactant support may modify [131] the apparent kinetic behaviour. 

Attempts have also been made to obtain the radicals (CF3)3C and CeFs as products of vacuum pyrolysis of (CF3)3CI and CeFsI (Butler and Snelson, 1980b). However, only perfluoroisobutene was observed in an IR spectrum of pyrolysis products of (CF3)3CI. Thermolysis of CeFsl led to formation of CF4, CF3 and CF2 as a result of decomposition of the aromatic ring. This behaviour was explained as due to catalytic effects which take place on the platinum reactor surface. 

Hydrogenation of 3,4-hexanedione was used to compare the behaviour of different supported platinum catalysts. The highest rate has been obtained over Pt/MCM-41 catalyst. It was the only catalysts, where the rate constant k2 exceeded ki, i.e., there was no catalyst deactivation during the catalytic run. It is... 

The use of equation (3.2) to study the behaviour of catalysts is known as solid electrolyte potentiometry (SEP). Wagner38 was the first to put forward the idea of using SEP to study catalysts under working conditions. Vayenas and Saltsburg were the first to apply the technique to the fundamental study of a catalytic reaction for the case of the oxidation of sulfur dioxide.39 Since then the technique has been widely used, with particular success in the study of periodic and oscillatory phenomena for such reactions as the oxidation of carbon monoxide on platinum, hydrogen on nickel, ethylene on platinum and propylene oxide on silver. 

Ertl, G. (1989). The oscillatory catalytic oxidation of carbon monoxide on platinum surfaces. In Spatial inhomogeneities and transient behaviour in chemical kinetics, (ed. P. Gray, G. Nicolis, F. Baras, P. Borckmans, and S. K. Scott), ch. 37, pp. 563—76. Manchester University Press. 

Considerable potential exists to design surface modified electrodes which can mimic the behaviour of electronic components. For example, a rectifying interface can be produced by using two-layer polymer films on electrodes. The electroactive species in the layers have different redox potentials. Thus electron transfer between the electrode (e.g. platinum) and the outer electroactive layer is forced to occur catalytically by electron transfer mediation through the inner electroactive layer. 

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