Automobile exhaust. See

Japanese chemists succeeded in obtaining good yields of methane by reaction of H2 with a mixture of carbon monoxide and carbon dioxide, at temperatures as low as 270 °C, by use of a special mixed catalyst containing nickel as the most important metallic constituent. Why is nickel used In the same vein, why is platinum or platinum-rhodium alloy (but not nickel) used in catalytic converters for automobile exhausts (See also Section 17.4.)... 

The oxidizing ability of ozone can be highly detrimental, especially when it is present in the pollution from automobile exhausts (see Section 5.11). 

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). 

Plot these results on log-probability coordinates and estimate the mean and standard deviation for each distribution (see Appendix C). What kind of averages are these quantities How do the weekend and weekday particle size distributions compare with respect to the location and width of the maximum The weekend results are attributed to automobile exhaust, whereas the weekday results are assumed to be diluted by aerosols from outside the tunnel. 

We can observe this process by analyzing polluted air at various times during a day (see Fig. 5.28). As people drive to work between 6 and 8 a.m., the amounts of NO, N02, and unburned molecules from petroleum increase. Later, as the decomposition of N02 occurs, the concentration of ozone and other pollutants builds up. Current efforts to combat the formation of photochemical smog are focused on cutting down the amounts of molecules from unburned fuel in automobile exhaust and designing engines that produce less nitric oxide (see Fig. 5.29). 

Catalysts for automobile exhaust systems are designed to remove environmental pollutants such as unburned hydrocarbons, CO formed from incomplete combustion and oxides of nitrogen. Three-way catalysts are based on Pt and Rh together with various additives that together perform a complex series of reactions, including removal of hydrocarbons by oxidation and steam re-forming (see above), and... 

An extreme good similarity was reported for the isomeric pattern of the tetra- and penta-CDFs found in automobile exhausts and in emissions from MSW incinerators (12) and steel mills, see Figure... 

Although ozone concentrations in the upper atmosphere play an important role in protecting Earth s surface from harmful UV radiation, ozone at its surface is a pollutant harmful to human health. Enhanced levels of surface ozone are often the result of automobile exhaust and pose a serious health risk. Eortunately, current levels of surface ozone (also known as smog) over most major cities have declined to healthier levels due in part to domestic and international governmental regulations, see also Atmospheric Chemistry. 

There is considerable literature concerning catalysis of the NO + CO and NO + H2 reactions over Rh and Pt in various forms. A general conclusion is that the latter reaction is substantially fester than the former with Rh [1,2] and especially Pt [1-4] under equivalent conditions. With respect to NO removal, the presence of CO inhibits the NO + H2 reaction [1-6], see also [7], Rather surprisingly there appears to be no definitive studies of the mixed NO, CO, H2 reaction system [7] even though all three gases are simultaneously present in automobile exhaust gases. 

Heterogeneous catalysis is also utilized in the catalytic converters in automobile exhaust systems. The exhaust gases, containing compounds such as nitric oxide, carbon monoxide, and unburned hydrocarbons, are passed through a converter containing beads of solid catalyst (see Fig. 12.16). The catalyst promotes the conversion of carbon monoxide to carbon dioxide, hydrocarbons to carbon dioxide and water, and nitric oxide to nitrogen gas to lessen the environmental impact of the exhaust gases. However, this beneficial catalysis can, unfortunately, be accompanied by the unwanted catalysis of the oxidation of SO2 to SO3, which reacts with the moisture present to form sulfuric acid. 

Heterogeneous catalysis is also used in the catalytic converters of automobile exhaust systems. The exhaust gases, containing compounds such as nitric oxide, carbon monoxide, and unburned hydrocarbons, are passed through a converter containing beads of solid catalyst (see Fig. 15.18). The... 

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