Nitrogen dioxide heterogeneous reactions

Sakamaki, F., S. Hatakeyama, and H. Akimoto, Formation of Nitrous Acid and Nitric Oxide in the Heterogeneous Dark Reaction of Nitrogen Dioxide and Water Vapor in a Smog Chamber, Int. J. Chem. Kinet., 15, 1013-1029 (1983). 

Fan, Z., R. M. Kamens, J. Zhang, and J. Hu, Ozone-Nitrogen Dioxide-NPAH Heterogeneous Soot Particle Reactions and Modeling NPAH in the Atmosphere, Environ. Sci. Technol., 30, 2821-2827 (1996a). 

The choice of an appropriate model is heavily dependent on the intended application. In particular, the science of the model must match the pollutant(s) of concern. If the pollutant of concern is fine PM, the model chemistry must be able to handle reactions of nitrogen oxides (NOx), sulphur dioxide (SO2), volatile organic compounds (VOC), ammonia, etc. Reactions in both the gas and aqueous phases must be included, and preferably also heterogeneous reactions taking place on the surfaces of particles. Apart from correct treatment of transport and diffusion, the formation and growth of particles must be included, and the model must be able to track the evolution of particle mass as a function of size. The ability to treat deposition of pollutants to the surface of the earth by both wet and dry processes is also required. 

In the Ostwald process ammonia is catalytically oxidized in a heterogeneous reaction. The key steps in the process are 1) Oxidation of ammonia to nitric oxide (NO), 2) Oxidation of NO to nitrogen dioxide (NO2) and 3) Absorption ofN02 in water to produce nitric acid. These steps are summarized in the following sections91,97. 

Zirconium dioxide and zeolites of pentasil structure are widely used as catalysts and efficient carriers in many heterogeneous reactions, and particularly in the process of selective catalytic reduction of nitrogen oxides by hydrocarbons (SCR-process) [1,2]. Synthesis of new catalytic systems for NOx SCR-process by CnHm is therefore related with searching for their optimum composition and preparation methods to attain maximum activity in this reaction. 

Poschl, U., Letzel, T., Schauer, C., Niessner, R. Interaction of ozone and water vapor with spark discharge soot aerosol particles coated with benzo[a]pyrene O3 and H2O adsorption, benzofm] pyrene degradation, and atmospheric implications. J. Phys. Chem. A 105, 4029-4041 (2001) Prince, A.P., Wade, J.L., Grassian, V.H., Kleiber, K.D., Young, M.A. Heterogeneous reactions of soot aerosols with nitrogen dioxide and nitric acid atmospheric chamber and Knudsen cell smdies. Atmos. Environ. 36, 5729-5740 (2002)... 

Reasons for interest in the catalyzed reactions of NO, CO, and COz are many and varied. Nitric oxide, for example, is an odd electron, hetero-nuclear diatomic which is the parent member of the environmentally hazardous oxides of nitrogen. Its decomposition and reduction reactions, which occur only in the presence of catalysts, provide a stimulus to research in nitrosyl chemistry. From a different perspective, the catalyzed reactions of CO and COz have attracted attention because of the need to develop hydrocarbon sources that are alternatives to petroleum. Carbon dioxide is one of the most abundant sources of carbon available, but its utilization will require a cheap and plentiful source of hydrogen for reduction, and the development of catalysts that will permit reduction to take place under mild conditions. The use of carbon monoxide in the development of alternative hydrocarbon sources is better defined at this time, being directly linked to coal utilization. The conversion of coal to substitute natural gas (SNG), hydrocarbons, and organic chemicals is based on the hydrogen reduction of CO via methanation and the Fischer-Tropsch synthesis. Notable successes using heterogeneous catalysts have been achieved in this area, but most mechanistic proposals remain unproven, and overall efficiencies can still be improved. 

Sulfur dioxide (SO ) and nitrogen oxides (NO ) are oxidized to sulfate and nitrate aerosols either homogeneously rn the gas phase or heterogeneously in atmospheric microdroplets and hydrometeors Gas-phase production of nitric acid appears to be the dominant source of aerosol nitrate because the aqueous phase reactions of NO (aq) are slow at the nitrogen oxide partial pressures typically encountered in the atmosphere (5,i5). Conversely, field studies indicate that the relative importance of homogeneous and heterogeneous SO2 oxidation processes depends on a variety of climatological factors such as relative humidity and the intensity of solar radiation (4, -1 ). 

Heterogeneous catalysts are in a different physical state than the reaction medium, so they are easily separated from the product however, they often work at high temperatures and pressures that are more energy intensive on large industrial scales. An example of a heterogeneous catalyst is a catalytic converter (solid) that catalyzes the transformation of toxic combustion products to less toxic carbon dioxide (CO2), nitrogen (N2), and water (H2O). 

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