Catalytic converters, in automobiles

One of the most important apphcations of palladium is to catalyze hydrogenation, dehydrogenation, and petroleum cracking. Such reactions are widely employed in organic syntheses and petroleum refining. Palladium and platinum are installed in catalytic converters in automobiles to cut down the emission of unsaturated hydrocarbon gasses. 

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. 

The oxidation of CO to CO2 by metal-oxide clusters has received quite some attention, in part due to its relevance for the catalytic converters in automobiles, in part also because carbon monoxide is often used as a probe molecule in surface science and the reasonable simplicity of the system may still permit adequate theoretical treatments. In addition to the various systems involving PtmO cations as well as PtmO anions (see above), considerable efforts have been devoted to cluster anions of silver and gold, as reviewed recently [87]. A particular highlight is a conceptual catalytic cycle for the Au2 -mediated oxidation of CO with molecular oxygen, for which... 

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

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

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,... 

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 unburned hydrocarbons, are passed through a converter containing beads of solid catalyst (see 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. 

Typical ceramic materials produced on a co-rotating twin screw extruder are for example catalyst carriers. They are commonly shaped into granules for use as bulk material in reactors in the chemical industry or into honeycombs for catalytic converters in automobiles exhaust systems (Fig. 12). After extrusion, the catalyst carriers are cut oversized in the lineal direction, dried and then cut to the proper length. Afterwards the binder is removed and the carriers are calcinated or sintered. Finally, to provide them with catalytic properties, they are impregnated with an active film in a bath [Fri76]. 

The metal-mediated two-electron reduction of NO to the less toxic species N2O (Equation 8), N2 and ammonia in the global nitrogen cycle by bacteria and fungi, or in catalytic converters in automobiles has received a great deal of attention. 

The use, since 1975, of catalytic converters in automobiles has resulted in increased exhaust gas temperatures, up to 870°C (1600°F), with metal temperatures up to 760 °C (1400 F), as well as increased concentrations of corrosive chemicals, such as sulfuric acid, in the exhaust gas stream. As a result, materials resistant to high-temperature oxidizing conditions, such as hot dip aluminum-coated type 409 stainless steel, are being used in automotive exhaust systems [35-37]. 

Heterogeneous catalysis has a role in the atmospheric chemistry of ozone in the troposphere as well. Catalytic converters in automobiles are filled with a porous ceramic material, which provides a surface that catalyzes the removal of CO and NO (nitrogen oxides) ftom the exhaust. (Nitrogen oxides initiate the formation of ozone and other lung irritants in photochemical smog. We will examine this process in detail in Section 11.8.) The process by which catalytic converters operate is shown in Figure 11.14. The types of steps shown there are found in most examples of heterogeneous catalysis. 

Carbon monoxide in auto exhaust is the result of incomplete combusting of gasoline in the engine. The removal of this major pollutant from auto emissions by conversion to CO2 via this reaction is one of the primary functions of catalytic converters in automobiles.)... 

In heterogeneous catalysis, the reactants and the catalyst are in different phases. The catalyst is usually a solid, and the reactants are either gases or liquids. Heterogeneous catalysis is by far the most important type of catalysis in industrial chemistry, especially in the synthesis of many important chemicals. Heterogeneous catalysis is also used in the catalytic converters in automobiles. 

These reactions are important in catalytic converters in automobiles. Calculate AG° for each at 298 K. Predict the effect of increasing temperature on the magnitude of AG°. 

Catalysis is an essential aspect of about 90% of all chemical manufacturing processes, and the transition metals are often the key elements in the catalysts used. For example, Ni is used in the hydrogenation of oils (page 1079) Pt, Pd, and Rh are used in catalytic converters in automobiles (page 958) Fe304 is the main component of the catalyst used in the synthesis of ammonia (Focus On 15-1, www.masteringchemistry.com) and is used in the conversion of 802(g) to 803(g) in the manufacture of sulfuric acid (page 1061). 

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