Platinum catalysts carbon monoxide oxidation

Potentiometric techniques have been used to study autonomous reaction rate oscillations over catalysts and carbon monoxide oxidation on platinum has received a considerable amount of attention43,48,58 Possible explanations for reaction rate oscillations over platinum for carbon monoxide oxidation include, (i) strong dependence of activation energy or heat of adsorption on coverage, (ii) surface temperature oscillations, (iii) shift between multiple steady states due to adsorption or desorption of inert species, (iv) periodic oxidation or reduction of the surface. The work of Sales, Turner and Maple has indicated that the most... 

Oxidation. Carbon monoxide can be oxidized without a catalyst or at a controlled rate with a catalyst (eq. 4) (26). Carbon monoxide oxidation proceeds explosively if the gases are mixed stoichiometticaHy and then ignited. Surface burning will continue at temperatures above 1173 K, but the reaction is slow below 923 K without a catalyst. HopcaUte, a mixture of manganese and copper oxides, catalyzes carbon monoxide oxidation at room temperature it was used in gas masks during World War I to destroy low levels of carbon monoxide. Catalysts prepared from platinum and palladium are particularly effective for carbon monoxide oxidation at 323 K and at space velocities of 50 to 10, 000 h . Such catalysts are used in catalytic converters on automobiles (27) (see Exhaust CONTHOL, automotive). 

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

Goodman, M. G., Kenney, C. N., Morton, W., Cutlip, M. B. and Mukesh, D., 1982, Transient studies of carbon monoxide oxidation over platinum catalyst. Surf. ScL 120, L453-460. 

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). 

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. 

HIE) Liao, P. C., Wolf, E. E. Self-Sustained Oscillations During Carbon Monoxide Oxidation 1982 on a Platinum/y-Aluminum Oxide Catalyst. Chem. Eng. Commun. 13(4-6), 315-326... 

S.E. Voltz and D. Liederman, "Thermal Deactivation of a Platinum Monolithic Carbon Monoxide/Hydrocarbon Oxidation Catalyst", Ind. Eng. Chem. Prod. Res. Dev.. 1974,1314). 243-250. 

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.

Akubuiro, E. C., Verykios, X. E. Lesnick, L. Dispersion and snpport effects in carbon monoxide oxidation over platinum. App/ied Catalysis 14, 215-227 (1985). Stara, L, Nehasil, V. MatoUn, V. The influence of particle size on CO oxidation on Pd/alumina model catalyst. Surface Science 331—333, 173—177 (1995). 

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. 

Rate measurements on these catalysts imply the following conclusions The synergism between the noble metal and the oxidic component is due to spillover of oxygen. The oxygen adsorption sites are neither exclusively located on platinum nor on the three phase boundary. The rate determining step of the carbon monoxide oxidation should be the migration of adsorbed oxygen. 

A mathematical model of a wall-catalyzed reactor is used to elucidate the effects of Inlet velocity and concentration, geometry of the duct, and axial conduction on the hysteresis, multiplicity and parametric sensitivity. The monolith reactor for carbon monoxide oxidation is the prototype considered, with wall catalyst being platinum on alumina on a ceramic substrate. 

Almost all catalytic converters have to contend with the decay or poisoning of the catalyst In some form and the catalytic monolith Is no exception. Indeed this Is notorious In the automotive application where the catalytic converter must survive 50,000 miles of operation and still perform adequately. Although we shall use the kinetics of carbon monoxide oxidation over a platinum catalyst as an obvious and Important example, our main objective Is to develop a model which can handle any catalyst decay question and to point out the differences In two types of poisoning. Thus our study comes within the third main division of the subject as laid out by Butt (1 ) In 1972 not the mechanism or rate determination but the effect of deactivation on the operation of the reactor. 

A unique proposed applieation for an yttria-stabilized zirconia is in carbon monoxide detection. A platinum electrode is attached on both sides of a zirconia electrolyte. One side is covered with a platinum eatalyst on a porous alxunina substrate and the Pt electrode is not in direct contact with the sample gas. Platinum on the substrate acts as a catalyst for CO oxidation. A cross-sectional view of the CO sensor is shown in fig. 15 (Okamoto et al. 1980) (the operating temperature is around 300°C). When carbon monoxide exists in the atmosphere, most will be eatalytically oxidized by the oxygen in air during difiusion through the porous substance. Therefore, the gas that reaches the Pt electrode is not CO but a CO2-O2 mixture. On the other hand, on the surface of the platinum electrode without the catalyst, carbon monoxide is oxidized to CO2 and causes an anomalous EMF. This potential shows a one-to-one correspondence to the CO concentration. The typical performance of the CO sensor in air at 300°C is shown in fig. 16 (Okamoto et al. 1980). The EMF output increases with the CO content, but the slope of the curve decreases gradually. This sensor can operate at temperatures between 260 and 350 C and no speeial O2 reference gas is necessary. 

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