Carbon monoxide oxidation kinetics

Lanthanum cobaltate catalysts carbon monoxide oxidation, kinetics, 36 281-283... 

The purpose of this article is to review the results of transient low pressure studies of carbon monoxide oxidation over transition metal substrates. Particular emphasis is given to the use of in-situ electron spectroscopy, flash desorption, modulated beam and titration techniques. The strengths and weaknesses of these will be assessed with regard to kinetic insight and quantification. An attempt will be made to identify questions that are ripe for investigation. Although not limited to it, the presentation emphasizes our own work. A very recent review of the carbon monoxide oxidation reaction C l) will be useful to readers who are interested in a more comprehensive view. 

Just as in gas phase kinetics, reactive molecular beam-surface scattering is providing important molecular level insight into reaction dynamics. There is no surface reaction for which such studies have proven more illuminating than the carbon monoxide oxidation reaction. For example Len, Wharton and co-workers (23) found that the product CO exits a 700K Pt surface with speeds characteristic of temperatures near 3000K. This indicates that the CO formed by the reactive encounter of adsorbed species is hurled off the surface along a quite repulsive potential. 

Just as in the case of the H2-D2 exchange on ZnO, two mechanisms are also discernible for the carbon monoxide oxidation [stage (b)] on nickel oxide below 300°C. There is a low-temperature mechanism operative between 100° and 180°C. characterized by a low activation energy of 2 kcal./mole and a high-temperature mechanism, above 180°C., with a higher activation energy of 13 kcal./mole. The kinetics are different and are respectively ... 

The detailed chemistry of hydrogen and carbon monoxide oxidation is well established [152,291,442], and chemical kinetic modeling can be used confidently for these reaction systems to predict behavior over a wide range of conditions. 

Carbon Monoxide Oxidation. Analysis of the carbon monoxide oxidation in the boundary layer of a char particle shows the possibility for the existence of multiple steady states (54-58). The importance of these at AFBC conditions is uncertain. From the theory one can also calculate that CO will bum near the surface of a particle for large particles but will react outside the boundary layer for small particles, in qualitative agreement with experimental observations. Quantitative agreement with theory would not be expected, since the theoretical calculations, are based on the use of global kinetics for CO oxidation. Hydroxyl radicals are the principal oxidant for carbon monoxide and it can be shown (73) that their concentration is lowered by radical recombination on surfaces within a fluidized bed. It is therefore expected that the CO oxidation rates in the dense phase of fluidized beds will be suppressed to levels considerably below those in the bubble phase. This expectation is supported by studies of combustion of propane in fluidized beds, where it was observed that ignition and combustion took place primarily in the bubble phase (74). More attention needs to be given to the effect of bed solids on gas phase reactions occuring in fluidized reactors. 

Holgate HR, Webley PA, Tester JW. Carbon monoxide oxidation in supercritical water the effects of heat transfer and the water-gas shift reaction on observed kinetics. Energy Fuels 1992 6 586-597. 

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). 

Bollinger, M.A. and M.A. Vannice (1996). A kinetic and drifts study of low-temperature carbon monoxide oxidation over Au-Ti02 catalysts. Applied Catalysis B-Environmental, 8(4), 417-443. 

Seravalli, J., Kumar, M., Lu, W.-P., and Ragsdale, S. W., 1997, Mechanism of carbon monoxide oxidation by the carbon monoxide dehydrogenase/acetyl-CoA syndiase from Clostridium thermoaceticum Kinetic characterization of the intermediates, Biochem. 36 11241fi 11251. 

The oxidation of carbon compounds is treated only very briefly and avoids the reactions of the carbon monoxide oxidation. Although kinetic studies of the phosphorus oxidation have not until now yielded any rate coeflScients, we have nonetheless included a survey of the work done because it is obvious that once a few rate coelficients have been unequivocally determined, the relationships discussed will then yield many other quantitative results. 

Howard J.B., Williams G.C., Fine D.H.. (1973) Kinetics of Carbon Monoxide Oxidation in Postflame Gases. // Symposium (Int.) on Combustion, Combustion Institute Pittsburgh... 

Howard J., Williams G., Fine D. (1973) Kinetics of carbon monoxide oxidation in postflame gases. 14 Symposium (Intemat.) on Combustion. The Combustion Institute, Pittsburgh, 975-986... 

Gavril, D. Katsanos, N.A. Karaiskakis, G. Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium catalysts. J. Chromatogr., A 1999, 852, 507-523. 

Reactions of carboxylates containing the more electropositive cations yield product carbonates, or sometimes the basic carbonates. Some of these salts, e.g., those of the alkali metals, melt before decomposition. The oxide products from decomposition of the lanthanide compounds may contain carbon deposited as a result of carbon monoxide disproportionation. Kinetic measurements must include due consideration of the possible retention of carbon dioxide by the product (as COj ) and the secondary reactions involved in carbon deposition. 

H. R. Holgate, P. A. Webley, J. W. Tester and R. K. Helling, Carbon Monoxide Oxidation in Supercritical Water The Effects of Heat Transfer and the Water-Gas Shift Reaction on Observed Kinetics, Energy Fuels, 6, 586-597 (1992). 

Catalytic properties in the reactions of carbon monoxide oxidation (all oxides) and butene oxidative dehydrogenation (iron oxides) were studied using a microreactor with the vibrofluidized bed of catalysts and pulse/flow kinetic installation [4], Catalytic activities were characterized by the reaction rate W (molec. COWs) in differential conditions and first-order rate constant K (dm butene (STP) /m -s-atm), respectively. 

IIIE) Keil, W., Wicke, E. Kinetic Instabilities in Carbon Monoxide Oxidation on Platinum... 

One of the inconveniences of TS-PFR methods is that it is difficult, in fact impossible, to compare conversions calculated using the fitted rate expression with raw TS-PFR data. This point was raised previously in connection with the investigation of carbon monoxide oxidation. One can simulate kinetic behaviour using the above equations and parameters to produce the expected isothermal behaviour of the system but not that observed in the experimental results that are obtained from the TS-PFR during temperature ramping. This is unavoidable and results from our lack of knowledge of the axial temperature profile in the experimental set-up. 

Classical analysis has demonstrated that a given quantity of active material should be deposited over the thinnest layer possible in order to minimize diffusion limitations in the porous support. This conclusion may be invalid for automotive catalysis. Carbon monoxide oxidation over platinum exhibits negative order kinetics so that a drop in CO concentration toward the interior of a porous layer can increase the reaction rate and increase the effectiveness factor to above one. The relative advantage of a thin catalytic layer is further reduced when one considers its greater vulnerability to attrition and to the deposition of poisons. 

Source From Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium catalysts, in J. Chromatogr. 

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.

Zheng X, Mantzaras J, Bombach R Kinetic interactions between hydrogen and carbon monoxide oxidation over platinum. Combust Flame 161 332—346, 2014. 

---