Catalytic converter nitric oxide

A range of metals and metal oxides catalyze the reduction of NO. The most successful reducing agent is synthesis gas since the catalytic process is relatively fast 184), unlike the catalyzed decomposition of NO to N2 and O2. The observed nitrogen-containing products depend on the catalytic system used Pd- and Pt-based catalysts convert NO to NH3 184) whereas iridium and ruthenium systems minimize ammonia production and convert nitric oxide to dinitrogen. 

By far the most important use of the platinum metals is for catalysis. The largest single use is in automobile catalytic converters. Platinum is the principal catalyst, but catalytic converters also contain rhodium and palladium. These elements also catalyze a wide variety of reactions in the chemical and petroleum industry. For example, platinum metal is the catalyst for ammonia oxidation in the production of nitric acid, as described in Pt gauze, 1200 K... 

Some of the important reactions in contemporary technology involve NO, which is a designation of N2O, NO, and NO2, and was one of the first examples in this book. The formation of these molecules in combustion processes is a major source of air pollution, and the catalytic oxidation of NH3 to NO on R surfaces is used to produce nitric acid, a major industrial chemical. The decomposition of NO, to N2 is a major process in the automotive catalytic converter. 

Platinum also is used extensively as a catalyst in hydrogenation, dehydrogenation, oxidation, isomerization, carbonylation, and hydrocracking. Also, it is used in organic synthesis and petroleum refining. Like palladium, platinum also exhibits remarkable abdity to absorb hydrogen. An important application of platinum is in the catalytic oxidation of ammonia in Ostwald s process in the manufacture of nitric acid. Platinum is installed in the catalytic converters in automobile engines for pollution control. 

SCR is a process by which NO gases in diesel exhausts can be reduced to levels that will meet future legislation. SCR is based on the reduction of NO in the catalytic converter by the injection of ammonia or urea into the exhaust gases before they enter the catalytic converter, where NO and NHj react to form and H O. The ammonia injection process may be controlled by measuring either the ammonia or nitric oxide slip after the catalytic converter. Such an ammonia sensor should be able to tolerate contaminants such as particles in the exhaust gases and should show very low cross sensitivity to NO and HC. Typical diesel exhaust contains 3-9% CO 50-250 ppm CO, 6-12% O, 200-1,000 ppm NO, and 130-260 ppm HC. Furthermore, the response to NH3 should have a time constant in the order of 1 second. 

C. G. Vayenas and R. D. Farr, Science 208, 593 (1980), describe a solid electrolyte fuel cell in which ammonia is the fuel and is catalyt-ically converted at 1000 K with oxygen (or air) to nitric oxide. The idea is that the energy released in this step in industrial nitric acid production (Section 9.4) could be recovered directly as electricity. 

The processes going on inside this ceramic catalytic converter include the reactions shown in the insert. Fragments of unburned hydrocarbons and carbon monoxide and nitric oxide molecules are converted to less noxious substances, such as nitrogen and carbon dioxide, by reactions at the surface of the catalyst. 

Catalysts are of enormous importance, both in the chemical industry and in living organisms. Nearly all industrial processes for the manufacture of essential chemicals use catalysts to favor formation of specific products and to lower reaction temperatures, thus reducing energy costs. In environmental chemistry, catalysts such as nitric oxide play a role in the formation of air pollutants, while other catalysts, such as platinum in automobile catalytic converters, are potent weapons in the battle to control air pollution. 

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... 

Rain with a pH less than 5.6 is known as acid rain. Acid rain is caused by burning fossil fuels (especially coal) and by fertilizers used in intensive agriculture. These activities emit sulfur and nitrogen in gas compounds that are converted to sulfur oxides and nitrogen oxides. These in turn create sulfuric acid and nitric acid in rain. Acid rain may also be created from gases emitted by volcanoes and other natural sources. Acid rain harms fish and trees and triggers the release of metal ions from minerals into water that can harm people. The problem of acid rain in the United States has been addressed in recent decades by the use of scrubbers in coal burning power plants and catalytic converters in vehicles. 

Reduction of nitric oxide by carbon monoxide was first reported to occur at low temperature (252-369 K) over gold powder (0.86 m2 g-1) 30 the rate was maximal at 314 K, and nitric oxide inhibited the reaction. This paper also provides an early indication of the activity of gold for the oxidation of carbon monoxide near ambient temperature. Nitric oxide reduction occurs in this way in catalytic converters for the treatment of engine exhaust gases 9... 

Okay. These are the reactions we want to happen, and they do happen somewhat as the byproducts of the engine leave the exhaust. The problem is that they don t happen all that quickly, leaving bad stuff heading out into the atmosphere. That s why we use catalysts that lower the activation energies for these reactions and help them proceed at a rapid rate. A catalytic converter is inserted in the exhaust system of a car so that it receives the bad stuff after it s left the engine. The catalytic converter contains a ceramic core coated with very expensive metals—platinum, rhodium, and palladium—and has two sections. The first section deals with nitrogen oxide and nitric oxide. 

Not all catalysts need the extended smface provided by a porous structure, however. Some are sufficiently active so that the effort required to create a porous catalyst would be wasted. For such situations one type of catalyst is the monolithic catalyst. Monolithic catalysts are normally encountered in processes where pressure drop and heat removal are major considerations. Typical examples include the platinum gauze reactor used in the ammonia oxidation portion of nitric acid manufacture and catalytic converters used to oxidize pollutants in automobile exhaust. They can be porous (honeycomb) or non-porous (wire gauze). A photograph of a automotive catalytic converter is shown in Figure CD 11-2. Platinum is a primary catalytic material in the monolith. 

Deamination. On exposure to nitric oxide and a catalytic amount of oxygen the amino group of arylamines and heterarylamines is removed. Similarly, arylhydrazines are converted to the hydrocarbons although aryl azides are also formed as minor products. ... 

Other known chemical poisons for the HTS catalyst are halides, although under normal operating conditions they are not present in the feed at an appreciable concentration. Decay in the catalytic activity was also observed with the feed gas which contained minor amounts of unsaturated hydrocarbons, oxygen, and nitric oxides. Under the HTS conditions these compounds were converted into a heavy carbonaceous residue deposited on to the surface of the catalyst, blocking access of the reactants to the catalytic surface. 

Reduction of nitric oxide by carbon monoxide is one of the reactions occurring in catalytic converters for the purification of the engine exhaust gases [489] ... 

Diels-Alder reaction releasing, besides nitroxyl which can be converted to nitric oxide, a strongly blue fluorescent anthracene product 64 (Scheme 22) [99]. This reaction can therefore be followed sensitively in cell culture supernatants. Using early screening we have isolated seven different catalytic antibodies for the reaction out of approximately 12,000 individual cell culture wells resulting from fusions with ten different immunized mice. Due to early screening, the experiment was completed in a matter of weeks and comprised cloning of only a handful of antibodies [100]. 

If special conditions are required for a reaction to take place, such as the presence of a catalyst, the conditions or the catalyst can be written above or below the arrow. Platinum metal catalyzes (speeds up) the decomposition of nitric oxide to its constituent elements in catalytic converters. 

The interaction of SOD with peroxynitrite has been investigated. Perox5Tiitrite is produced by the reaction between nitric oxide and superoxide, whose concentration increases in pathological conditions such as ischemia. It has been found that peroxynitrite is also a substrate for SOD and that the catalytic action of the enzyme permanently modifies Tjrr-110 and converts it into 3-nitrotyrosine (78). The X-ray structure of the peroxynitrite-modified SOD has also been solved (see Section II,G). 

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