Converters Reduce Automobile Emissions

Often, Canadians do not appreciate or approve of government efforts to reduce automobile emissions. Some people were angry wben, decades ago, the government asked them to switch to unleaded gasoline. Even now, many people remove factory-installed, pollution-reducing resonators and catalytic converters from their new cars. They do this in an effort to increase the power of their vehicles. 

Summarizing there are both economic and technical reasons to explain the growing interest in Pd-containing catalytic converters to reduce automobile emissions. Main results of a long term development program are shown in this study. 

Emission Control Technologies. The California low emission vehicle (LEV) standards has spawned iavestigations iato new technologies and methods for further reducing automobile exhaust emissions. The target is to reduce emissions, especially HC emissions, which occur during the two minutes after a vehicle has been started (53). It is estimated that 70 to 80% of nonmethane HCs that escape conversion by the catalytic converter do so during this time before the catalyst is fully functional. 

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... 

Catalytic converters in automobile exhaust systems reduce emissions of oxides of nitrogen. 

Platinum group elements (PGE) are used as catalysts in a variety of industrial, chemical and pharmaceutical applications, such as in the production of pesticides and dye stuffs and in the processing of polymers. These rare noble metals, notably platinum (Pt), rhodium (Rh) and palladium (Pd), are also used as catalysts in automobile catalytic converters to reduce the emission of carbon monoxide (CO), nitrogen oxides (NOJ and hydrocarbons (HC) in exhaust fumes. This application, in fact, accounts for the largest consumption of the global supply of these metals on a per weight basis. In 2008, for instance, catalytic converter producers consumed a total of 52, 47 and 86% of the world s Pt, Pd and Rh, respectively (Matthey 2008). Pd use by the catalyst industry increased by a factor of six from 1993 to 2008 (Matthey 1996, 2008). 

The chemical and thermal characteristics of PGE make them highly useful as catalysts in a wide variety of industrial, chemical, electrical and pharmaceutical processes (Johnson Matthey 2007). Their use as catalysts in automotive catalytic converters to reduce noxious emissions from the burning of fossil fuels has undoubtedly been one of the most far-reaching and important applications. Automobiles have been equipped with catalytic converters since 1975 and 1986 in the US and Europe, respectively. Initially, Pt and Pd were used to reduce hydrocarbon and carbon monoxide emissions. Since the early 1990s, Rh has also been used in various combinations and ratios with Pt and Pd in three-way catalytic converters to reduce emissions. PGE appear to be emitted together with alumina particles from the washcoat as a result of various chemical, physical and... 

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.)... 

Legislation has greatly reduced the amount of automobile emissions, the main moving source of air pollution. The reduction in emissions has been accomplished through catalytic converters to treat exhaust gases and improvements in the efficiency of automobile engines. 

The largest and fastest growing application of palladium is in the production of automobile catalytic converters, which reduce harmful emissions from the engine. In a modern converter three reactions occur ... 

Reduction in the amount of pollutant gases from automobile emissions is a worldwide concern. To decrease the amount of pollutant gases, a catalytic converter is installed into the exhaust gas stream of automobiles. The catalyst is called a three-w catalyst. The gases which cause air pollution in the exhaust are hydrocarbons, carbon monoxide and nitric oxides. The catalyst oxidizes both hydrocarbons and carbon monoxide into CO2 and H2O, and also reduces nitric oxides into nitrogen. Decrease of these three main pollutant gases is presented in fig. 1 (Oohata 1990, Adachi 1991). 

Three-way catalytic converters (TWC) are designed to reduce three types of harmful automobile emissions carbon monoxide (CO), unburned hydrocarbons in the fuel (HC), and nitrogen oxides (NOx). The term nitrogen oxides refers to both NO2 and NO. The TWC accomplishes these tasks using precious metal catalysts (platinum, palladium, and rhodium) for chemical reactions that take place at high temperatures (e.g., 1000-1600°F) and short residence times (-0.05 s). 

One important use of catalysts is in catalytic converters on automobiles, which reduce the emission of exhaust gas pollutants such as carbon monoxide (CO), nitrogen oxides (NO., where x is variable), and unburned hydrocarbons. (See the chapter-opening diagrams and photograph for this chapter.) Air is introduced into the exhaust emissions from the automobile engine this mixture of gases then passes over the catalyst, which on its surface adsorbs molecules of CO, NO , and O2. The NO dissociates into N and O atoms, whereas the O2 dissociates into its atomic species. Pairs of nitrogen atoms combine to form N2 molecules, and carbon monoxide is oxidized to form... 

Automotive Catalytic Converter Catalysts. California environmental legislation in the early 1960s stimulated the development of automobile engines with reduced emissions by the mid-1960s, led to enactment of the Federal Clean Air Act of 1970, and resulted in a new industry, the design and manufacture of the automotive catalytic converter (50). Between 1974 and 1989, exhaust hydrocarbons were reduced by 87% and nitrogen oxides by 24%. 

Recent automobile exhaust emissions standards are summarized in Table III, and a review of the catalytic systems designed to meet these standards has recently appeared (26). Catalytic converters have been used as a part of emission control systems since 1975. One approach has been to use a dual bed catalytic converter where the reduction of NO to N2 occurs over the first bed, and excess O2 is provided to the second bed to oxidize the CO and hydrocarbons more completely. Typically, the exhaust contains compounds listed in Table IV plus some poisons containing Pb, P, S etc, (27). The catalytic system must reduce concentrations of CO, hydrocarbon and NOx to legally acceptable levels. 

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