Exhaust streams, automobile nitrogen oxides

Tests were run on a small ejtperimental reactor used for decomposing nitrogen oxides in an automobile exhaust stream. In one series of tests, a nitrogen stream containing various concentrations of NOj was fed to a reactor and the kinetic data obtained are shown in Figure P5-11. Each point represents one complete run. The reactor operates essentially as an isothermal backmix reactor (CSTR). What can you deduce abmit the apparent order of the reaction over the temperature range studied ... 

Another example is the solid catalyst used to reduce the emission of pollutants such as unburned hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust streams of automobile engines (Fig. 18.16). A catalytic converter is designed to simultaneously oxidize hydrocarbons and CO through the reactions... 

Solutions have not been limited to water, however. Atmospheric pollution from automobiles has decreased dramatically in the last 25 years since the development and deployment of the catalytic converter (Box 2-1). Modern three-way catalysts can simultaneously reduce the concentrations of carbon monoxide, hydrocarbons, and nitrogen oxides in the automobile s exhaust stream. Also, new methods for remediation of contaminated soils have been provided by the selection of unique plants and microbes for this purpose. 

In this chapter, we used a simplified equation for the combustion of gasoline. But the products generated in the operation of real automobile engines include various oxides of nitrogen, and it is desirable to remove these compounds from the exhaust stream rather than release them into the atmosphere. Currently this is done by the catalytic converter, but other technologies are being explored. One possible method involves the use of isocyanic acid, HNCO, which reacts with NO2 to produce N2, CO2, and H2O, as shown in the equation below ... 

The catalysts were evaluated by exposure to a simulated automobile exhaust gas stream composed of 0.2% isopentane, 2% carbon monoxide, 4% oxygen and a balance of nitrogen. The temperature required to oxidize the isopentane and carbon monoxide was used to compare catalyst performance. The chromium-promoted catalyst oxidized isopentane at the lowest temperature, and a mixed chromium/copper-promoted catalyst proved the most efficient for oxidizing carbon monoxide and isopentane. It is interesting to note that the test rig used a stationary engine with 21 pounds of catalyst. Although the catalyst was very effective it is difficult to envisage uranium oxide catalysts employed for emission control of mobile sources. 

Reduction in the amount of pollutant gases from automobile emissions is a worldwide concern. To decrease the amount of pollutant gases, a catalytic converter is installed into the exhaust gas stream of automobiles. The catalyst is called a three-w catalyst. The gases which cause air pollution in the exhaust are hydrocarbons, carbon monoxide and nitric oxides. The catalyst oxidizes both hydrocarbons and carbon monoxide into CO2 and H2O, and also reduces nitric oxides into nitrogen. Decrease of these three main pollutant gases is presented in fig. 1 (Oohata 1990, Adachi 1991). 

---