Platinum supported catalysts, carbon monoxide

Mukesh, D., Kenney, C. N., and Morton, W. (1983). Concentration oscillations of carbon monoxide, oxygen and 1-butene over a platinum supported catalyst. Chem. Eng. Sci., 38, 69-77. 

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. 

The adsorption of CO on a series of platinum based catalysts was also carried out by microcalorimetry technique, supplying information about the number, the strength distribution and the heat associated to the carbon monoxide adsorption on available Pt surface sites. Table 12.2 lists some literature reports on the average heats of CO adsorption over different platinum supported catalysts. In this table, the experimental data on powdered catalysts were collected from the vicinity of room temperature up to 130 C. Prior to CO adsorption, the samples were reduced at 200 or 500 C under hydrogen flow. 

Transition-metal organometallic catalysts in solution are more effective for hydrogenation than are metals such as platinum. They are used for reactions of carbon monoxide with olefins (hydroformyla-tion) and for some ohgomerizations. They are sometimes immobihzed on polymer supports with phosphine groups. 

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

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. 

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 ... 

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... 

Nuclear magnetic resonance (NMR) spectroscopy continues to gain importance in catalyst characterization, and van der KJink contributes the first chapter on metal NMR to the Advances the focus is on supported platinum catalysts, including those with adsorbed carbon monoxide or hydrogen. The method provides evidence of metal dispersions and distinguishes between hydrogen on the metal and hydrogen on the support. 

R.K. Herz and S.P. Marin, Surface chemistry models of carbon monoxide on supported platinum catalysts, / Catal. 65 281 (1980). 

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