Automobile exhaust, carbon monoxide from

Standing on a street comer in any major city exposes a person to above-normal concentrations of carbon monoxide from automobile exhaust. Carbon monoxide also reacts with hemoglobin. The following reaction takes place in the capillaries of the lung. 

For example, take six samples of carbon monoxide from the exhaust of an idling automobile and obtain the CO percentages as shown in Table 32-1. The sample mean is... 

Carbon monoxide from automobile exhausts Photochemical oxidants, particularly ozone (Los Angeles)... 

This reaction serves for removal of carbon monoxide from gas mixtures and is usually carried out over supported metal catalysts. In reforming techniques, carbon monoxide, poisonous for the catalyst in fuel cells, is removed in such a way. It is also applied in automobiles for reducing the exhaust gas carbon monoxide to an environmentally acceptable level. 

In fact, most of us benefit from the use of catalysis. Automotive catalytic converters have represented the most massive application of environmental catalysis and one of the most challenging and successful cases in catalysis, generally. Automobile catalysts deseive a few more comments. The engine exhaust emission is a complex mixture, whose composition and flow rate change continuously depending on a variety of factors such as driving conditions, acceleration, and speed. Despite the variability of the conditions, three-way catalysts have achieved the reduction of exhaust carbon monoxide, hydrocarbons, and... 

Catalysts are materials that speed up chemical reactions or even enable them to proceed without themselves being consumed. An example of a catalyst is the one located in the catalytic converter of an automobile exhaust system that consists of small quantities of precious metals coated onto the solid honeycomb-like surface that acts as a catalyst support. Such a catalyst speeds the reaction with oxygen of toxic carbon monoxide from the engine exhaust to produce nontoxic carbon dioxide ... 

Oxidation. Carbon monoxide can be oxidized without a catalyst or at a controlled rate with a catalyst (eq. 4) (26). Carbon monoxide oxidation proceeds explosively if the gases are mixed stoichiometticaHy and then ignited. Surface burning will continue at temperatures above 1173 K, but the reaction is slow below 923 K without a catalyst. HopcaUte, a mixture of manganese and copper oxides, catalyzes carbon monoxide oxidation at room temperature it was used in gas masks during World War I to destroy low levels of carbon monoxide. Catalysts prepared from platinum and palladium are particularly effective for carbon monoxide oxidation at 323 K and at space velocities of 50 to 10, 000 h . Such catalysts are used in catalytic converters on automobiles (27) (see Exhaust CONTHOL, automotive). 

Carbon monoxide is found in varying concentrations in unventilated and confined spaces resulting from partial oxidation of carbonaceous matter. Burning wood, paper, kerosene, or other organic materials in inadequate air can produce this gas. It also is found in automobile exhaust and tobacco smoke emissions. 

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... 

However, the effects from automobile exhausts in these cities are similar to those in industrial cities of advanced countries, because many vehicles have a high weight-to-horsepower ratio and are often old and poorly maintained. The horsepower of 85% of the cars in India is between 10 and 14, and 60% of all vehicles are more than 10 years old. Vehicle maintenance is poor because spare parts are expensive or unavailable, and technical competence is low. Consequently, pollution is out of all proportion to the number of cars in circulation. Carbon monoxide peaks of 100 ppm have been recorded at street level at major intersections. As the number of vehicles continues to increase, it is expected that oxidant pollution may become a problem in other cities if control measures are not introduced. 

Figure 8 Typical design of a three-way catalyst for automobile exhaust control. Highlighted here are the honeycomb support and the mounting can used. So-called three-way catalysts, consisting of a combination of Pt, Rh, and Pd particles dispersed on high surface area alumina, are spread on the honeycomb structure to oxidize the carbon monoxide and unbumed hydrocarbons and to reduce the nitrogen oxides released by the engine of the car. (Reprinted from Ref 52, 1998, with permission from Elsevier)...

To remove oxides of nitrogen (assumed to be NO) from automobile exhaust, a scheme has been proposed that uses unbumed carbon monoxide (CO) in the exhaust to reduce the NO over a solid catalyst, according to the reaction... 

Photochemical smog also contains unbumed hydrocarbons and carbon monoxide, both of which come from the exhaust of automobile engines. These pollutants can be reduced or eliminated from the atmosphere in a variety of ways. Cleaner running engines and catalytic converters greatly reduce NO and hydrocarbon levels. Strict federal tailpipe emission standards are encouraging automobile manufacturers to develop new cars that are powered by electricity or alternative fuels such as natural gas. 

Propane is a colorless, highly flammable/explosive gas that is heavier than air. It occurs in natural gas at concentrations from 3% to 18%. It is emitted into the atmosphere from furnaces, automobile exhausts and sources of natural gas. With sufficient oxygen, it is combusted to carbon dioxide and water but carbon monoxide, a deadly gas, will be generated under leaner conditions. Some references state that propane is odorless while others provide an odor threshold of 22 000-36 000 mg m (odor index = 425 at 20°C). In air, 1 ppm propane = 1.83 mg m. ... 

Ethanol from cellulose represents an enormous opportunity to make a transportation fuel that is an alternative to gasoline. Development of such a fuel is motivated by 1) an increased cleanliness of automobile exhaust, with decreased levels of carbon monoxide and nitrous oxides, 2) a need for a fuel that does not contribute to an increase in the Greenhouse effect, 3) the desire to decrease the dependence of the United States on imported petroleum, and 4) the possibility of creating wealth in regions where cellulose is a prevalent natural resource. 

Catalytic converters in automobile exhaust systems were developed to remove some of the carbon monoxide and unburned hydrocarbons from automobile exhaust. A catalyst is any substance that speeds a chemical reaction without being permanendy altered itself Some of the transition metals, such as platinum, palladium, iridium, and rhodium,... 

Solutions have not been limited to water, however. Atmospheric pollution from automobiles has decreased dramatically in the last 25 years since the development and deployment of the catalytic converter (Box 2-1). Modern three-way catalysts can simultaneously reduce the concentrations of carbon monoxide, hydrocarbons, and nitrogen oxides in the automobile s exhaust stream. Also, new methods for remediation of contaminated soils have been provided by the selection of unique plants and microbes for this purpose. 

Several catalyst samples of tungsten carbide and W,Mo mixed carbides with different Mo/W atom ratios, have been prepared to test their ability to remove carbon monoxide, nitric oxide and propane from a synthetic exhaust gas simulating automobile emissions. Surface characterization of the catalysts has been performed by X-ray photoelectron spectroscopy (XPS) and selective chemisorption of hydrogen and carbon monoxide. Tungsten carbide exhibits good activity for CO and NO conversion, compared to a standard three-way catalyst based on Pt and Rh. However, this W carbide is ineffective in the oxidation of propane. The Mo,W mixed carbides are markedly different having only a very low activity. 

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