Reduction of nitrogen oxide

Pollution control such as the reduction of nitrogen oxides, halocarbons and hydrocarbons from flue gases [37] is another important field of plasma-assisted chemistry using non-thennal plasmas. The efficiency of plasma chemical reactions can be enhanced by introducing catalysts into the plasma [38, 39]. 

The first commercial appHcation of precious metals for the reduction of nitrogen oxides in power plant emission control was in 1989. W. R. Grace s... 

TABLE 25-25 Advantages and Disadvantages of Selective Catalytic Reduction of Nitrogen Oxides... 

Selective Catalytic Reduction of Nitrogen Oxides The traditional approach to reducing ambient ozone concentrations has been to reduce VOC emissions, an ozone precurssor. In many areas, it has now been recognized that ehmination of persistent exceedances of the National Ambient Air Qnality Standard for ozone may reqnire more attention to reductions in the other ingredients in ozone formation, nitrogen oxides (NOJ. In such areas, ozone concentrations are controlled by NO rather than VOC emissions. 

Reactions involving the catalytic reduction of nitrogen oxides are of major environmental importance for the removal of toxic emissions from both stationary and automotive sources. As shown in this section electrochemical promotion can affect dramatically the performance of Rh, Pd and Pt catalysts (commonly used as exhaust catalysts) interfaced with YSZ, an O2 ion conductor. The main feature is strong electrophilic behaviour, i.e. enhanced rate and N2 selectivity behaviour with decreasing Uwr and , due to enhanced NO dissociation. 

It has been reported that titanium supported vanadium catalyst is active for ammonia oxidation at temperatures above 523 K [2,3]. Also, supported vanadium oxides are known to be efficient catalyst for the catalytic reduction of nitrogen oxides (NO ) in the presence of ammonia [4]. This work investigates the nanostructured vanadia/Ti02 for low temperature catalytic remediation of ammonia in air. 

Since the pioneer work of Li and Armor (1,2,3), y ho found that methane could be used as a selective reductant of nitrogen oxide over Co-ZSM5, several sohds have been used with the same purpose (4,5,6,7). Metals such as Co, Rh and Pt, exchanged in ZSMS (8), were similarly studied. In the absence of the three metals have a high selectivity but when 25% of oxygen is added to the feed,... 

With the advance of three-way catalysis for pollution control, used mainly in automobile catalytic conversion but also for the purification of gas exhausts from stationary sources, a need has arisen to develop a basic understanding of the reactions associated with the reduction of nitrogen oxides on transition metal catalytic surfaces [1,2]. That conversion is typically carried out by using rhodium-based catalysts [3], which makes the process quite expensive. Consequently, extensive effort has been placed on trying to minimize the amount of the metal needed and/or to replace it with an alternatively cheaper and more durable active phase. However, there is still ample room for improvement in this direction. By building a molecular-level picture of theprocesses involved,... 

Less, but still significant, information is available on the surface chemistry of other nitrogen oxides. In terms of N20, that molecule has been shown to be quite reactive on most metals on Rh(110), for instance, it decomposes between 60 and 190 K, and results in N2 desorption [18]. N02 is also fairly reactive, but tends to convert into a mixed layer of adsorbed NO and atomic oxygen [19] on Pd(lll), this happens at 180 K, and is partially inhibited at high coverages. Ultimately, though the chemistry of the catalytic reduction of nitrogen oxide emissions is in most cases controlled by the conversion of NO. 

Beloshapkin, S.A., Matyshak, V.A., Paukshtis, E.A. et al. (1999) IR studies of the transformations of nitrogen-containing organic intermediates during selective reduction of nitrogen oxides by hydrocarbons, React. Kinet. Catal. Lett., 66, 297. 

Armor, J.N. (1995) Catalytic reduction of nitrogen oxides with methane in the presence of excess oxygen A review, Catal. Today, 26, 147. 

Matsumoto, S. (2000) Catalytic Reduction of Nitrogen Oxides in Automotive Exhaust Containing Excess Oxygen by NOx Storage-Reduction Catalyst, Cat. Tech., 4, 102. 

Wichterlova, B., Sazama, P., Breen, J.P. et al. (2005) An in situ UV-vis and FTIR spectroscopy study of the effect of H2 and CO during the selective catalytic reduction of nitrogen oxides over a silver alumina catalyst, J. Catal. 235, 195. 

Martin, J.A., Yates, M., Avila, P. et al. (2007) Nitrous oxide formation in low temperature selective catalytic reduction of nitrogen oxides with V205/Ti02 catalysts, Appl. Catal. B... 

Broer, S. and Hammer, T. (2000) Selective catalytic reduction of nitrogen oxides by combining a non-thermal plasma and a V205-W03/Ti02 catalyst, Appl. Catal. B Env. 28, 101-11. 

Demidouk, V., Ravi, V., Chae, J.-O. et al. (2005) Pt-Al203 catalyst and discharge plasma pre-treatment techniques for enhancing selective catalytic reduction of nitrogen oxides A comparative study, React. Kinet. Catal. Lett. 85, 239-44. 

Mok, Y.S., Koh, D.J., Shin, D.N. et al. (2004) Reduction of nitrogen oxides from simulated exhaust gas by using plasma-catalytic process, Fuel Process Technol. 86, 303-17. 

A procedure for preparation of sodium hyponitrite involving reduction of nitrogen oxide by the ketyl, followed by extraction into water [1], had been operated routinely on the small scale. A 41-fold scaled up run exploded and ignited after 200 ml of water had been added as part of the work-up. This was attributed to the presence of an unusually large proportion of coagulated unreacted sodium in the ketyl. Small-scale operation with precautions is urged [2],... 

Now, GC-IRMS can be used to measure the nitrogen isotopic composition of individual compounds [657]. Measurement of nitrogen isotope ratios was described by Merritt and Hayes [639], who modified a GC-C-IRMS system by including a reduction reactor (Cu wire) between the combustion furnace and the IRMS, for reduction of nitrogen oxides and removal of oxygen. Preston and Slater [658] have described a less complex approach which provides useful data at lower precision. Similar approaches have been described by Brand et al. [657] and Metges et al. [659]. More recently Macko et al. [660] have described a procedure, which permits GC-IRMS determination of 15N/14N ratios in nanomole quantities of amino acid enantiomers with precision of 0.3-0.4%o. A key step was optimization of the acylation step with minimal nitrogen isotope fractionation [660]. 

An interesting variant of selective oxidation catalysis is the catal)hic reduction of nitrogen oxides by ammonia or hydrocarbons. In this case the reducing molecule should specifically react with NO or NO2, that are present in very low concentrations, rather than become oxidized to CO2 + H2O by reacting with O2 that is present in much higher concentration. The distinction between oxo-ions and oxide particle is most convenient if these entities are present on a zeolite support. Techniques have been developed to study the interconversion by IR spectroscopy ... 

Adsorption of nitric and sulfuric acids on ice particles provides the sol of the nitrating mixture. An important catalyst of aromatic nitration, nitrous acid, is typical for polluted atmospheres. Combustion sources contribute to air pollution via soot and NO emissions. The observed formation of HNO2 results from the reduction of nitrogen oxides in the presence of water by C—O and C—H groups in soot (Ammann et al. 1998). As seen, gas-phase nitration is important ecologically. 

Voorhoeve, RJH Remeika, JP Johnson, DWJr. Rare-earth manganites catalysts with low ammonia yield in the reduction of nitrogen oxides. Science, 1973, Volume 180, 62-64. 

Yokoyama, C. and Misono, M. Catalytic reduction of nitrogen oxides by propene in the presence of oxygen over cerium ion-exchanged zeolites II. Mechanistic study of roles of oxygen and doped metals. J. Catal, 1994, Volume 150,9-17. 

As mentioned earlier, the oxidation of carbon monoxide and hydrocarbons should be achieved simultaneously with the reduction of nitrogen oxides. However, the first reaction needs oxygen in excess, whereas the second one needs a mixture (fuel-oxygen) rich in fuel. The solution was found with the development of an oxygen sensor placed at exhaust emissions, which would set the air-to-fuel ratio at the desired value in real time. So, the combination of electronics and catalysis and the progress in these fields led to better control of the exhaust emissions from automotive vehicles. 

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