Nitrogen monoxide catalytic converter

Sulfur dioxide and any oxide of nitrogen. 8 Catalytic converters break down harmful oxides of nitrogen present in exhaust fumes to nitrogen and convert carbon monoxide to carbon dioxide, and so purify the gases let (2)... 

The burning of fuel in a car engine produces a variety of pollutants, such as carbon monoxide, unbumed hydrocarbons and nitrogen oxides. Catalytic converters change these compounds into more environmentally friendly compounds. Although tetraethyllead (Pb(C2H5)4) has been used as an additive which can be used to Improve the antiknock properties of fuel (leaded petrol), it stops the platinum catalyst In a catalytic converter from functioning. Leaded petrol should therefore not be used In a car that contains a catalytic converter. 

However, such a level can still be considered too high for vehicles having 3-way catalytic converters. In fact, results observed in the United States (Benson et al., 1991) and given in Figure 5.20 show that exhaust pollutant emissions, carbon monoxide, hydrocarbons and nitrogen oxides, increase from 10 to 15% when the sulfur level passes from 50 ppm to about 450 ppm. This is explained by an inhibiting action of sulfur on the catalyst though... 

In principle, the catalytic converter is a fixed-bed reactor operating at 500—620°C to which is fed 200—3500 Hters per minute of auto engine exhaust containing relatively low concentrations of hydrocarbons, carbon monoxide, and nitrogen oxides that must be reduced significantly. Because the auto emission catalyst must operate in an environment with profound diffusion or mass-transfer limitations (51), it is apparent that only a small fraction of the catalyst s surface area can be used and that a system with the highest possible surface area is required. 

High levels of sulfur not only form dangerous oxides, but they also tend to poison the catalyst in the catalytic converter. As it flows over the catalyst in the exliaust system, the sulfur decreases conversion efficiency and limits the catalyst s oxygen storage capacity. With the converter working at less than maximum efficiency, the exhaust entering the atmosphere contains increased concentrations, not only of the sulfur oxides but also, of hydrocarbons, nitrogen oxides, carbon monoxides, toxic metals, and particulate matter. 

Another example is the use of catalytic metals (platinum and rhodium) in the catalytic converter of a motor car. These solid metals catalyse the reaction between the pollutant gases carbon monoxide and nitrogen monoxide. 

Houdry s solution to the problem was the first catalytic converter ever designed for an automotive vehicle. The catalytic converters found on almost all cars and trucks in use today are still strikingly similar to his invention. Exhaust gases passed into the converter and over a bed of platinum catalyst, then exited with a greatly reduced concentration of carbon monoxide, nitrogen oxides, and unburned hydrocarbons. Houdry obtained a patent for his device in 1956 and founded a company, Oxy-Catalyst, to manufacture and sell the new product. 

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. 

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... 

European regulations state that all new cars have to be fitted with catalytic converters as part of their exhaust system (Figure 7.15). Car exhaust fumes contain pollutant gases such as carbon monoxide (CO) formed from the incomplete combustion of hydrocarbons in the fuel, and nitrogen(n) oxide (NO) formed by the reaction of nitrogen gas and oxygen gas from the air. The following reactions proceed of their own accord but very slowly under the conditions inside an exhaust. 

Catalysts help customers comply cost-effectively with clean-air regulations. Hydrocarbons, carbon monoxide, and nitrogen oxides can be removed using supported precious metal catalysts. Organic sulfur compounds are converted to H2S using nickel/molybdenum or cobalt/molyb-denum on alumina catalysts. Sulfur can be recovered in a Claus process unit. The Claus catalytic converter is the heart of a sulfur recovery plant. 

Haber s breakthrough was to find the catalyst, a facilitator for the reaction, which in this specific case was an iron and iron oxide solid— rust. Solid catalysts can facilitate reactions because molecules are three-dimensional beasts, and when it comes to reactions, orientation matters. This restriction can be understood by considering interactions between other three-dimensional objects a kiss is just a kiss, but three-dimensional humans have to be oriented correctly for the kiss to be on target and effective. One advantage of a solid catalyst may be that it can hold the reactants in a favorable orientation. Automobiles use catalytic converters to convert NOx back into nitrogen and oxygen and convert poisonous carbon monoxide to carbon dioxide. 

In recent years the sulfur dioxide content of the air has risen, and so also have the nitrogen dioxide levels. This is due to increased use of fossil fuels and the fact that oxides of nitrogen are produced when some fuels and other materials burn in petrol engines. Catalytic converters on car exhausts help to reduce the amount of the oxides of nitrogen and carbon monoxide in the air, and so help to lower car emission pollution . 

Catalytic converters are used to decrease nitrogen oxides, carbon monoxide, and hydrocarbons in exhaust. Leaded gasoline and extreme temperatures decrease their effectiveness. 

When a combustion engine converts fuel into energy, the reactions of the combustion process are incomplete. Incomplete combustion results in the production of poisonous carbon monoxide and undesirable nitrogen oxides. Since 1975, catalytic converters have reduced the exhaust emissions that contribute to air pollution by approximately 90%. 

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... 

---