Nitric from heterogeneous oxidation

Jensen, A., Johnsson, J.E., and Dam-Johansen, K. (1993) Formation of Nitric Oxide and Nitrous Oxide from Heterogeneous Oxidation of Hydrogen Cyanide at Fluidized Bed Combustion Conditions. 12 Int. Conf. on Fluidized bed Combustion, ASME, New York, 447-454. 

Presently, there is a general consensus that heterogeneous catalytic processes play an important role in environmental issues regarding their high selectivity towards the removal of undesired side products, such as atmospheric pollutants, in comparison with that obtained from non-catalysed processes. However, such a benefit could be disputed in the future with the implementation of severe restrictions on standard emission of those atmospheric pollutants, particularly nitric oxide, which is a very challenging aspect. 

The turbulent mixing of emitted reactant gas (such as nitric oxide) with atmospherically formed reactant gas (such as ozone) results in macroscopic heterogeneities, which under some circumstances can significantly change the reaction rate from the value that the mean concen-... 

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. 

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... 

D-xylose on hydrolysis with dilute nitric acid. Percival and Chanda7 isolated a xylan from the same plant. They found that the methylated xylan produced on hydrolysis 2-methyl-D-xylose, 2,3-dimethyl-D-xylose, 2,4-dimethyl-D-xylose and 2,3,4-trimethyl-D-xylose. From this and from the results of periodate oxidation, Percival and Chanda considered that the polysaccharide contains 1 — 3 and 1 —> 4 linkages with a non-reducing endgroup (yielding the 2,3,4-trimethyl-D-xylose) for every 20-21 D-xylose units. They considered that this xylan was not a mixture of 1 —> 3 and 1 —> 4 linked polysaccharides because careful fractionation of its diacetate and dimethyl ether failed to establish any polymer heterogeneity. Barry, Dillon, Hawkins and O Colla74 confirmed the conclusion of Percival and Chanda. 

In many cases, the NOx family is formed as the sum of NO and N02, and accounts for the most reactive nitrogen species. The NOx/ NOy concentration ratio, which is often reported from field observations, is an indicator of the reactivity of odd nitrogen and its ability to destroy stratospheric ozone (or to affect other chemical families including chlorine and bromine compounds). The value of this ratio increases with altitude above 30 km to reach a value of nearly one in the upper stratosphere and mesosphere. It decreases substantially when the stratospheric aerosol load is enhanced, for example, after large volcanic eruptions (Fahey et al, 1993), and substantial amounts of nitrogen oxides are converted to nitric acid by heterogeneous reaction (5.152). It is also low in the polar regions, especially in air masses processed by polar stratospheric clouds. 

The short life of NO and its low concentration in biological systems make the measurement of this molecule a challenging analytical problem. Among several methods (biochemical assays, UV-Visible spectroscopy, chemiluminescence, EPR) electrochemical methods are considered to be the most suitable for in situ detection of NO in biological milieu. " Generally, the electrochemical oxidation of nitric oxide on solid electrodes proceeds via a two-step (EC mechanism) with an electrochemical reaction as the initial step (heterogenous electron transfer) followed by a chemical reaction. The first electrochemical step is a one-electron transfer from a NO molecule to the electrode residting in the formation of a nitrosonium ion ... 

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