Nitric oxide reduction carbon monoxide effect

Here we shall briefly summarize the effects of individual poisons on various catalytic reactions taking place on automotive catalysts. There are three main catalytic processes oxidation of carbon monoxide and hydrocarbons and reduction of nitric oxide. Among secondary reactions there are undesirable ones which may produce small amounts of unregulated emissions, such as NH3, S03 (6), HCN (76, 77), or H2S under certain operating conditions. Among other secondary processes which are important for overall performance, in particular of three-way catalysts, there are water-gas shift, hydrocarbon-steam reforming, and oxygen transfer reactions. Specific information on the effect of poisons on these secondary processes is scarce. 

The noncatalytic reduction of nitric oxide by insitu formed char is considered one of the significant reactions which control nitric oxide emission and a detailed kinetic study was carried out. (2, 3, 4) The present authors demonstrated that this reaction proceeded even under an excess air condition and that the rate is enhanced by the coexisting oxygen up to 750°C. (.5,6) Besides the noncatalytic reaction, carbon monoxide may have a significant effect on nitric oxide reduction by char. (2.) Roberts et al.(8) reported that the gas phase reactions in the nitric oxide reduction play a minor role and that the absence of a major gas phase reaction of NO and coal nitrogen into N2 requires the participation of a surface which catalyzes reactions. Char is considered to... 

Effect of Carbon Monoxide on Nitric Oxide Reduction by Char, The effects of carbon monoxide on nitric oxide reduction by char was analyzed by changing the gas flow rate of the reactant and the ratio of concentration of carbon monoxide to nitric oxide at the inlet of the reactor. This ratio defined as a was chosen to be three extreme cases a = 4-W. 16, a = 47.8, and a 91.6-V98.9. The initial series of experiments were carried out for O 4-V. 6... 

Platinum is an effective oxidation catalyst for carbon monoxide and the complete oxidation of hydrocarbons. Palladium also promotes the oxidation of carbon monoxide and hydrocarbons but is more sensitive to poisoning than platinum in the exhaust environment. Both platinum and palladium promote the reduction of nitric oxide but are less effective than rhodium. In addition to the noble metals, three-way catalysts contain the base metal cerium and possibly other additives such as lanthanum, nickel or iron. These base metal additives are believed to improve catalyst performance by extending conversion during the rapid air-fuel ratio perturbations and help to stabilize the alumina support against thermal degradation. 

From the results of other authors should be mentioned the observation of a similar effect, e.g. in the oxidation of olefins on nickel oxide (118), where the retardation of the reaction of 1-butene by cis-2-butene was greater than the effect of 1-butene on the reaction of m-2-butene the ratio of the adsorption coefficients Kcia h/Kwas 1.45. In a study on hydrogenation over C03O4 it was reported (109) that the reactivities of ethylene and propylene were nearly the same (1.17 in favor of propylene), when measured separately, whereas the ratio of adsorption coefficients was 8.4 in favor of ethylene. This led in the competitive arrangement to preferential hydrogenation of ethylene. A similar phenomenon occurs in the catalytic reduction of nitric oxide and sulfur dioxide by carbon monoxide (120a). 

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