Carbon monoxide oxidation, platinum supported catalysts

IX yer, S. M. Transient infrared studies of carbon monoxide oxidation on a supported platinum catalyst. M. S. Thesis, University of Connecticut, 1980. 

K. Grass and H. G. Lintz, The kinetics of carbon monoxide oxidation on tin(TV) oxide supported platinum catalysts, J. Catal. 172, 446-452 (1997). 

Carbon-supported Pt can also be used as the anode catalyst. However, this requires pure H2. Contaminants such as carbon monoxide (CO) poison the catalyst, because CO can strongly adsorb on Pt, blocking the catalytic sites and reducing platinum s catalytic activity. In H2 produced from the reforming of other fuels, CO is always present. Thus, to improve contaminant tolerance, carbon-supported PtRu was developed and now is always used as the anode catalyst. Ru can facilitate the oxidation of CO, releasing the catalytic sites on Pt through the following reactions ... 

Fig. 4 Energy distribution function, (p(e t) (cmol/kJ/mol/), against the dimensionless product of the lateral interaction energy (P) and the local isotherm (0)P0, for carbon monoxide adsorption over a bimetalhc Pto.25-Rho.75 silica supported catalyst, at 698 K. Source From Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium catalysts, in J. Chromatogr.

Mukesh, D., Cutlip, M.C., Goodman, M., Kenney, C.N., Morton, W., 1982. The stability and oscillations of carbon monoxide oxidation over platinum supported catalyst. Effect of butene. Chem. Eng. Sci. 37, 1807-1810. Mukesh, D., Kenney, C.N., Morton, W., 1983. Concentration oscillations of carbon monoxide, oxygen and 1-butene over a platinum supported catalyst. Chem. Eng. Sci. 38, 69-77. 

Nicholas, D. M., and Shah, Y. T. Carbon monoxide oxidation over a platinum-porous fiber glass supported catalyst. Ind. Eng. Chem. Prod. Res. Dev. 15(1), 35-40, 1976. 

If a chemical reaction is operated in a flow reactor under fixed external conditions (temperature, partial pressures, flow rate etc.), usually also a steady-state (i.e., time-independent) rate of reaction will result. Quite frequently, however, a different response may result The rate varies more or less periodically with time. Oscillatory kinetics have been reported for quite different types of reactions, such as with the famous Belousov-Zha-botinsky reaction in homogeneous solutions (/) or with a series of electrochemical reactions (2). In heterogeneous catalysis, phenomena of this type were observed for the first time about 20 years ago by Wicke and coworkers (3, 4) with the oxidation of carbon monoxide at supported platinum catalysts, and have since then been investigated quite extensively with various reactions and catalysts (5-7). Parallel to these experimental studies, a number of mathematical models were also developed these were intended to describe the kinetics of the underlying elementary processes and their solutions revealed indeed quite often oscillatory behavior. In view of the fact that these models usually consist of a set of coupled nonlinear differential equations, this result is, however, by no means surprising, as will become evident later, and in particular it cannot be considered as a proof for the assumed underlying reaction mechanism. 

Dynamic reactor studies are not new, but they have not been widely used in spite of the fact that they can provide a wealth of information regarding reaction mechanisms. In this research, oxidation of carbon monoxide over supported cobalt oxide (C03O4) was studied by both dynamic and conventional steady state methods. Among metal oxides, cobalt oxide is known to be one of the most active catalysts for CO and hydrocarbon oxidation, its activity being comparable to that of noble metals such as palladium or platinum. 

Stonehart examined highly dispersed platinum and alloys of Pt-Pd7a73 and found that with sophisticated catalyst preparation techniques, it was possible to maintain very small crystallites of these binary alloys on carbon supports, and that the alloys were more active than Pt alone for hydrogen oxidation in the presence of both carbon monoxide and... 

Supported platinum catalysts have been used to promote the oxidation of alkenes in water at 180°C and two atmospheres of oxygen to give the 1,2 diols. Oxidation of ethylene gave a mixture of the diol and acetic acid in about a 2 1 ratio. Oxidation of propene gave the diol as the predominant product with some acetone also produced. When a small amount of carbon monoxide was added to... 

Galwey AK, Bettany DG, Mortimer M (2006) Kinetic compensation effects observed during oxidation of carbon monoxide on y-alumina supported palladium, platinum, and rhodium metal catalysts toward a mechanistic explanation. Int J Chem Kin 38 689... 

While many studies have been performed for the oxidation of methanol and carbon monoxide on supported catalyst systems [66,99-103] and Pt-Ru bulk alloys [61,104— 107], relatively few studies have been initiated on single-crystal platinum surfaces modihed with ruthenium. Of those performed these have largely involved the investigation of platinum single crystals modihed by ruthenium dosed electro-chemically [92,93] or spontaneously [80-82,90,91] from aqueous chloride solutions. This approach is discussed in Section 5.4. 

The selective production of methanol and of ethanol by carbon monoxide hydrogenation involving pyrolysed rhodium carbonyl clusters supported on basic or amphoteric oxides, respectively, has been discussed. The nature of the support clearly plays the major role in influencing the ratio of oxygenated products to hydrocarbon products, whereas the nuclearity and charge of the starting rhodium cluster compound are of minor importance. Ichikawa has now extended this work to a study of (CO 4- Hj) reactions in the presence of alkenes and to reactions over catalysts derived from platinum and iridium clusters. Rhodium, bimetallic Rh-Co, and cobalt carbonyl clusters supported on zinc oxide and other basic oxides are active catalysts for the hydro-formylation of ethene and propene at one atm and 90-180°C. Various rhodium carbonyl cluster precursors have been used catalytic activities at about 160vary in the order Rh4(CO)i2 > Rh6(CO)ig > [Rh7(CO)i6] >... 

Chin, P., Sun, X., Roberts, G.W., and Spivey, JJ. Preferential oxidation of carbon monoxide with iron-promoted platinum catalysts supported on metal foams. Applied Catalysis. A, General, 2006, 302, 22. 

The influence of the support is undoubted and spillover was further confirmed by the excess of hydrogen chemisorbed by a mechanical mixture of unsupported alloy and TJ-A1203 above that calculated from the known values for the separate components. It was also observed that the chemisorption was slower on the supported than on the unsupported metal and that the greater part of the adsorbate was held reversibly no comment could be made on the possible mediation by traces of water. On the other hand, spillover from platinum-rhenium onto alumina appears to be inhibited for ratios Re/(Pt Re) > 0.6. In an infrared investigation of isocyanate complexes formed between nitric oxide and carbon monoxide, on the surface of rhodium-titania and rhodium-silica catalysts, it seems that the number of complexes exceeded the number of rhodium surface atoms.The supports have a pronounced effect on the location of the isocyanate bond and on the stability of the complexes, with some suggestion of spillover. 

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