Nitric oxide from automobile exhaust

The main use of rhodium is with platinum in catalysts for oxidation of automobile exhaust emissions. In the chemical industry, it is used in catalysts for the manufacture of ethanoic acid, in hydroformylation of alkenes and the synthesis of nitric acid from ammonia. Many applications of iridium rely on... 

Ozone is produced in substantial concentrations by industrial activity and, indirectly, from automobile exhausts. The most important sequence of reactions producing tropospheric ozone begins with hydrocarbon vapors, nitric oxide, and sunlight ... 

Smog Formation. Nitrogen and oxygen react to form nitric oxide in the cylinder of automobile engines. The NO from automobile exhaust is oxidized to NO2 in the presence of peroxide radicals. 

Smog Formation. In Chapter 1. Problem PI-14. in the CD-ROM Sr, Web Module, we discussed a very simple model for smog removal in Ihe 1 basin by a Santa Ana wind. We will now look a little deeper into the chemi of smog formation. Nitrogen and oxygen react to form nitric oxide in the inder of automobile engine.s. The NO from automobile exhaust is oxidizei NOi in the presence of peroxide radicals. 

Nitric oxide was discovered by Van Helmont in 1620. It occurs in the exhaust gases from automobiles along with other oxides of nitrogen, at trace concentrations. It also is found in minute quantities in the upper atmos-... 

In the lower atmosphere, nitric oxide is probably the most important pollutant in urban air it is produced in internal-combustion engines and is ejected into the atmosphere in the exhaust gases. Pollution from this source is certain to be augmented by the increase in the number of automobiles. The NO eventually is converted to NOz, although the details of the conversion are not clear. The obvious reaction with 02... 

Another important application of heterogeneous catalysts is in automobile catalytic converters. Despite much work on engine design and fuel composition, automotive exhaust emissions contain air pollutants such as unburned hydrocarbons (CxHy), carbon monoxide, and nitric oxide. Carbon monoxide results from incomplete combustion of hydrocarbon fuels, and nitric oxide is produced when atmospheric nitrogen and oxygen combine at the high temperatures present in an... 

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). 

Nitric oxide is formed in the combustion of fossil fuels and is present in the exhausts of automobiles and power plants it can also be formed from the action of lightning on atmospheric N2 and O2. In the atmosphere, NO is oxidized to NO2. These gases, often collectively designated NO, contribute to the problem of acid rain, primarily because NO2 reacts with atmospheric water to form nitric acid ... 

Compounds of nitrogen are also impurities in fossil fuels they bum to form nitric oxide, NO. Most of the nitrogen in the NO in exhaust gases from furnaces, automobiles, airplanes, and so on, however, comes from the air that is mixed with the fuel. 

Several catalyst samples of tungsten carbide and W,Mo mixed carbides with different Mo/W atom ratios, have been prepared to test their ability to remove carbon monoxide, nitric oxide and propane from a synthetic exhaust gas simulating automobile emissions. Surface characterization of the catalysts has been performed by X-ray photoelectron spectroscopy (XPS) and selective chemisorption of hydrogen and carbon monoxide. Tungsten carbide exhibits good activity for CO and NO conversion, compared to a standard three-way catalyst based on Pt and Rh. However, this W carbide is ineffective in the oxidation of propane. The Mo,W mixed carbides are markedly different having only a very low activity. 

Transition metal carbides (mainly of W and Mo) have been shown to be effective catalysts in some chemical reactions that are usually catalyzed by noble metals such as Pt and Pd (ref.1). Their remarkable physical properties added to lower cost and better availability could make them good candidates for substitute materials to noble metals in automobile exhaust catalysis. Hence, for this purpose, we have prepared several catalysts of tungsten carbide and W,Mo mixed carbides supported on y alumina with different Mo/W atom ratios. The surface composition has been studied by XPS while the quantitative determination of catalytic sites has been obtained by selective chemisorption of hydrogen and of carbon monoxide. The catalytic performances of these catalysts have been evaluated in the simultaneous conversion of carbon monoxide, nitric oxide and propane from a synthetic exhaust gas. 

Fig. 5-1. Variation with time of hydrocarbons, aldehydes, nitrogen oxides, ozone, and peroxyacetyl nitrate (PAN) for three conditions. Top Downtown Los Angeles during the course of a day with eye irritation composed of data presented in Leighton (1961) and Air Quality Criteria for Photochemical Oxidants (1970). Center Irradiation of automobile exhaust diluted with air in a smog chamber of a plastic bag exposed to sunlight composed of data from Leighton (1961, originally Schuck et al., 1958), Kopzcynski et al. (1972), Wilson et al. (1973), Miller and Spicer (1975), Jeffries et al. (1976), and Wayne and Romanofsky (1961). Bottom Smog-chamber irradiation of a mixture of propene, nitric oxide, and air. [Adapted from data presented by Altshuller et al. (1967) and Pitts el al. (1975).] Note differences in the time scales.

Catalytic converters are used in the exhaust system of automobiles and can reduce emissions of carbon monoxide and hydrocarbons by up to 90%. Carbon monoxide can be transformed into carbon dioxide, and unburned hydrocarbons from the fuel get burned on the metal surfaces. Nitric oxide, one of the main contributors to urban smog, will react with carbon monoxide to form carbon dioxide and nitrogen gas. These processes are conducted in catalytic converters. 

Mortar Deterioration. Mortar may decay from the formation of calcium sulfoaluminate (which causes expansion and loss of mortar strength) and by the attack of pollutants in the atmosphere. Portland cement contains tricalcium aluminate, which reacts with sulfates in solution to form calcium sulfoaluminate. Exhaust gases from automobiles contain sulfur dioxide, sulfur trioxide, and nitrous oxides. These oxides react with moisture in the atmosphere to form sulfurous acid, sulfuric acid, and nitric acid, which are the attacking agents. As attack continues over the years, the mortar joints may crack, the surface of the joint may spall off, and the mortar may become softer and more crumbly. 

Catalytic conversion of off-gases, e.g., the reduction of nitrous oxide from nitric acid plants, with anunonia and the use of "three way" catalyst in automobile exhausts. 

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