Catalytic converter unbumed hydrocarbons

With the advent of automobile catalytic converters, monolithic catalyst beds have been developed to convert unbumed hydrocarbons and carbon monoxide to combustion products. These oxidation reactions are highly exothermic. Thus, the catalyst is deposited only on the surface layers of the support. Other design considerations are a mechanically strong bed to withstand mechanical and thermal shock, and low pressure drop. These requirements led to monolithic catalyst beds of various configurations. 

Automobile catalytic converter. Catalytic converters contain a "three-way" catalyst designed to convart CO to CO2, unbumed hydrocarbons to CO2 and H2O. and NO to N2. The activa components of the catalysts are the precious metals platinum and rhodium palladium is sometimes used as well. 

The use of catalytic converters to reduce the amount of unbumed hydrocarbons in exhaust gases is an additional example of the use of metals. Reactions of these unbumed hydrocarbons in the atmosphere are described later, in the section on photochemical smog. The catalyst currently used is a cordierite or alumina support treated with an AI2O3 wash coat containing rare earth oxides and 0.10% to 0.15% Pt, Pd, and/or Rh, which catalyzes the combustion of hydrocarbons in the exhaust gases to carbon dioxide and water. Platinum,... 

All cars that are currently manufactured in the United States are built with catalytic converters, like the one shown in Figure 8, to treat the exhaust gases before they are released into the air. Platinum, palladium, or rhodium in these converters act as catalysts and increase the rate of the decomposition of NO and of NO2 into N2 and O2, harmless gases already found in the atmosphere. Catalytic converters also speed the change of CO into CO2 and the change of unbumed hydrocarbons into CO2 and H2O. These hydrocarbons are involved in the formation of ozone and smog, so it is important that unbumed fuel does not come out in the exhaust. 

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. 

The catalytic converters (Figure 16-17) built into automobile exhaust systems contain two types of heterogeneous catalysts, powdered noble metals and powdered transition metal oxides. They catalyze the oxidation of unbumed hydrocarbon fuel (reaction 1) and of partial combustion products such as carbon monoxide (reaction 2, shown in Figure 16-18). 

The three-way catalytic converter used in automobiles catalyzes the oxidation of unbumed hydrocarbons and CO while reducing simultaneously NO to N2 [198, 206]. Describe the process. 

The basic goal of the tliree-way catalytic converter system, is the simultaneous conversion of carbon monoxide, unbumed hydrocarbons and nitrogen oxides, that are the origin of many health and environmental problems. 

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. 

Auto emissions have been closely monitored, and strict controls have been put Into place to minimize the amount of unbumed hydrocarbons released into the atmosphere. The Clean Air Act of 1990 was passed to help reduce hydrocarbon emissions from automobiles. The catalytic converter was developed to help react the unburned hydrocarbon and produce a less dangerous emission of carbon dioxide and water. (As a side benefit, lead had to be eliminated from gasoline because it poisoned the catalyst and made the catal3dic converter useless. The big campaign to get the lead out removed a major source of the deadly heavy metal from the environment.)... 

All new cars are equipped with catalytic converters (Figure 14.25). An efficient catalytic converter serves two purposes It oxidizes CO and unbumed hydrocarbons to CO2 and H2O, and it reduces NO and NO2 to N2 and O2. Hot exhaust gases into which air has been injected are passed through the first chamber of one converter to... 

Heterogeneous catalysis is also utilized in the catalytic converters in automobile exhaust systems. The exhaust gases, containing compounds such as nitric oxide, carbon monoxide, and unbumed hydrocarbons, are passed through a converter containing beads of solid catalyst (Fig. 12.16). The catalyst promotes the conversion of carbon monoxide to carbon dioxide, hydrocarbons to carbon dioxide and water, and nitric oxide to nitrogen gas to lessen the environmental impact of the exhaust gases. However, this beneficial catalysis can, unfortunately, be accompanied by the unwanted catalysis of the oxidation of SO2 to SO3, which reacts with the moisture present to form sulfuric acid. 

The idea of using cataiysts to oxidize gases is not a new one. Cataiytic converters in cars oxidize caitwn monoxide and unbumed hydrocarbons to minimize pollution. Many substances are oxidized into new materials for manufacturing purposes. But both of these types of catalytic reactions oaur at very high temperatures. NASA s catalyst is special, because it s able to eliminate carbon monoxide at room temperature. 

The last example using heterogeneous catalysts is the one used in automobile catalytic converters. Catalytic converters are used to reduce the toxicity of emissions from an internal combustion engine. Chemical species found in engine exhaust are carbon monoxide (CO), unbumed hydrocarbons nitrogen oxides (NO ). 

As mentioned in Chapter 3, these products contribute to air pollution. The three-way catalytic converter simultaneously converts CO and unbumed hydrocarbons to CO and oxidizes NO to N, thereby reducing or eliminating most of the harmful emissions from the combustion engine for example, the oxidation of carbon monoxide to carbon dioxide,... 

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