Carbon monoxide oxidation rate constant

After heating to 623 K in helium, which also effected reduction according to XAFS, treatment with sodium cyanide solution removed the Au°, and left 10% of gold as cationic Au111.54 The specific rate of carbon monoxide oxidation was constant, irrespective of the treatment with sodium cyanide, as were activation energy and orders of reaction. It appeared that the Au111 was reduced under reaction conditions, and was not an active species. 

In combustion systems it is generally desirable to minimize the concentration of intermediates, since it is important to obtain complete oxidation of the fuel. Figure 13.5 shows modeling predictions for oxidation of methane in a batch reactor maintained at constant temperature and pressure. After an induction time the rate of CH4 consumption increases as a radical pool develops. The formaldehyde intermediate builds up at reaction times below 100 ms, but then reaches a pseudo-steady state, where CH2O formed is rapidly oxidized further to CO. Carbon monoxide oxidation is slow as long as CH4 is still present in the reaction system once CH4 is depleted, CO (and the remaining CH2O) is rapidly oxidized to CO2. 

While the photoenhancement of the hydrogen deuterium exchange at MgO has been found to be due solely to an increase in the rate constant, investigations of the photocatalyzed carbon monoxide oxidation with ZnO, NiO and Co304 as catalysts have shown that the photoenhancement in these cases is due to drastic changes in the apparent activation energy 82-88)... 

Figure 3. Global rate constant vs. 1/ t for carbon monoxide oxidation reaction (Eq. 19).

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. 

Jambunathan, K., Shah, B.C., Hillier, A.C. Scanning electrochemical microscopy of hydrogen electro-oxidation. Rate constant measurements and carbon monoxide poisoning on platinum. J. Electroanal. Chem. 2001, 500, 279-289. 

Reaction 2-6 is sufficiently fast to be important in the atmosphere. For a carbon monoxide concentration of 5 ppm, the average lifetime of a hydroxyl radical is about 0.01 s (see Reaction 2-6 other reactions may decrease the lifetime even further). Reaction 2-7 is a three-body recombination and is known to be fast at atmospheric pressures. The rate constant for Reaction 2-8 is not well established, although several experimental studies support its occurrence. On the basis of the most recently reported value for the rate constant of Reaction 2-8, which is an indirect determination, the average lifetime of a hydroperoxy radical is about 2 s for a nitric oxide concentration of 0.05 ppm. Reaction 2-8 is the pivotal reaction for this cycle, and it deserves more direct experimental study. 

The kinetics and mechanism for oxygen transfer between 4-cyano-V,V,-dimethylaniline V-oxide and a C2-capped mexo-tetraphenylporphyrinatoiron(III) and mc5 o-tetrakis(pentafiuorophenyl)-porphyrinatoiron(III) have been established. Addition of a copper(II) porphyrin cap to an iron(II)-porphyrin complex has the expected effect of reducing both the affinities and rate constants for addition of dioxygen or carbon monoxide. These systems were studied for tetradecyl-substituted derivatives solubilized by surfactants such as poly(ethylene oxide) octaphenyl ether. ... 

In this scheme, Reaction 1 represents a direct (pre-ignition) combustion reaction which may or may not be accompanied by formation of carbon monoxide Reaction 2 describes the oxidation reaction (and its sequences) examined in the present study. B and C in Reaction 2 denote degradation products of humic acids (e.g. hymatomelanic, fulvic, and/or so-called water soluble coal acids), and ki,, etc. represent the corresponding rate constants. 

Indeed, lattice parameters of both the copper and the zinc oxide were found to depend on the catalyst composition. The lattice extension of copper was attributed to alpha brass formation upon partial reduction of zine oxide, and an attempt was made to correlate the lattice constant of copper with the decomposition rate of methanol to methyl formate. Furthermore, the decomposition rate of methanol to carbon monoxide was found to correlate with the changes of lattice constant of zinc oxide. Although such correlations did not establish the cause of the promotion in the absence of surface-area measurements and of correlations of specific activities, the changes of lattice parameters determined by Frolich et al. are real and indicate for the first time that the interaction of catalyst components can result in observable changes of bulk properties of the individual phases. Frolich et al. did not offer an interpretation of the observed changes in lattice parameters of zinc oxide. Yet these changes accompany the formation of an active catalyst, and much of this review will be devoted to the origin, physicochemical nature, and catalytic activity of the active phase in the zinc oxide-copper catalysts. 

Whether or not CO can affect an increase in the oxidation rate of NO in the presence of hydrocarbons depends on the relative rates of these competing reactions. For a highly reactive hydrocarbon such as mesity-lene, the reaction of the hydrocarbon with hydroxyl radicals is so fast that the reaction of CO with OH cannot compete even at high CO-hydrocarbon ratios. For less reactive hydrocarbons such as ethylene and 1-butene, CO competes with the hydrocarbon for the OH radicals and, in systems containing these hydrocarbons, a carbon monoxide effect is possible. The rate constant for the reaction of ethylene with hydroxyl radicals has been measured to be 3.6 X 10 1/mole-sec 15). This is forty times greater than the rate constant of 8.9 X 10 1/mole-sec (JO) for the reaction of OH with CO. Therefore, a CO effect should be possible at CO-ethylene ratios of 40 or greater. Experimentally, an increase in the NO oxidation rate for this system was observed at a CO—hydrocarbon ratio of 50. 

DoUimore and Tonge [15] ascribed the deceleratory decomposition of zinc formate in air (0 < nr < 0.3) to an initial instantaneous and extensive nucleation of reactant crystalhte surfaces with product zinc oxide and the operation of a contracting sphere mechanism. For 0.3 < nr < 0.8 the reaction rate is almost constant, probably as a result of reactant cracking. for both processes is 67 kJ mol". During the course of reaction the yields of hydrogen and carbon monoxide increased, while that of carbon dioxide decreased. This was attributed to a decrease in the catalytic activity of the product oxide, possibly as a result of sintering. The formation of higher molecular mass products was mentioned. 

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