Rhodium, catalytic converter

Probably the most significant control technology breakthrough came m 1977, when Volvo released a computer-controlled, fuel-mjected vehicle equipped with a three-way catalyst. The new catalytic converters employed platinum, palladium, and rhodium to simultaneously reduce NO and oxidize CO and HC emissions under carefully controlled oxygen conditions. The new Bosch fuel injection system on the vehicle provided the precise air/fuel control necessary for the new catalyst to perform effectively. The combined fuel control and three-way catalyst system served as the foundation for emissions control on the next generation of vehicles. 

Perhaps the most familiar example of heterogeneous catalysis is the series of reactions that occur in the catalytic converter of an automobile (Figure 11.12). Typically this device contains 1 to 3 g of platinum metal mixed with rhodium. The platinum catalyzes the oxidation of carbon monoxide and unburned hydrocarbons such as benzene, C6H6 ... 

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. 

By far the most important use of the platinum metals is for catalysis. The largest single use is in automobile catalytic converters. Platinum is the principal catalyst, but catalytic converters also contain rhodium and palladium. These elements also catalyze a wide variety of reactions in the chemical and petroleum industry. For example, platinum metal is the catalyst for ammonia oxidation in the production of nitric acid, as described in Pt gauze, 1200 K... 

This review has highlighted the key contributions of modern surface science to the understanding of the kinetics and mechanism of nitrogen oxide reduction catalysis. As discussed above, the conversion of NO has been taken as the standard to represent other NOx, and CO has typically been used as the reducing agent in these studies. The bulk of the work has been carried out on rhodium and palladium surfaces, the most common transition metals used in three-way catalytic converters. 

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. 

Transition metals and their compounds are used as catalysts. Catalysts you may already know are Iron In the Haber process (Industrial production of ammonia) platinum in the Ostwald process (Industrial production of nitric acid) and platinum, rhodium and palladium In catalytic converters. 

When rhodium is combined with platinum and palladium, the elements together form the internal metals of automobile catalytic converters, which convert hot unburned hydrocarbon exhaust gases to less harmful CO and H O. Similar alloys are used to manufacture high-temperature products such as electric coils for metal refining furnaces and high-temperature spark plugs. 

Three-Way Catalytic Converter Acontainer in line within the gasoline engine exhaust system which contains platinum, palladium, and/or rhodium catalysts. These catalysts convert CO, NOx, and unbumed fuel to C02, H20, and N2. 

Japanese chemists succeeded in obtaining good yields of methane by reaction of H2 with a mixture of carbon monoxide and carbon dioxide, at temperatures as low as 270 °C, by use of a special mixed catalyst containing nickel as the most important metallic constituent. Why is nickel used In the same vein, why is platinum or platinum-rhodium alloy (but not nickel) used in catalytic converters for automobile exhausts (See also Section 17.4.)... 

A catalytic converter reduces the pollution caused by automobile exhaust by converting such harmful combustion products as NO, CO, and hydrocarbons to harmless N2, 02, and COz. The catalyst is typically platinum, Pt, palladium, Pd, or rhodium, Rd. 

The catalyst of an automotive catalytic converter is typically a form of platinum, Pt palladium, Pd or rhodium, Rd. The production of catalytic converters is by far the largest market for these precious and semiprecious metals. 

S. Zimmermann, A. von Bohlen, J. Messerschmidt, B. Sures, Accumulation of the precious metals platinum, palladium and rhodium from automobile catalytic converters in Paratenuisentis ambiguus as compared with its E>sh host, Anguilla Anguilla, J. Helminthol., 79(1) (2005), 85 D89. 

Complex oxides of the perovskite structure containing rare earths like lanthanum have proved effective for oxidation of CO and hydrocarbons and for the decomposition of nitrogen oxides. These catalysts are cheaper alternatives than noble metals like platinum and rhodium which are used in automotive catalytic converters. The most effective catalysts are systems of the type Lai vSrvM03, where M = cobalt, manganese, iron, chromium, copper. Further, perovskites used as active phases in catalytic converters have to be stabilized on the rare earth containing washcoat layers. This then leads to an increase in rare earth content of a catalytic converter unit by factors up to ten compared to the three way catalyst. 

Supported rhodium is used in many catalytic processes, and rhodium is an active component in the automobile catalytic converter (rhodium catalyzes the reduction of NO to N2, as well as the oxidization of CO to CO2) (1), which explains the large number of investigations of adsorption under UHV (e.g., references cited in Reference (403)). As rhodium surfaces are able to dissociate CO (373-375), CO adsorption may be accompanied by CO dissociation. CO dissociation on rhodium is... 

Trisubstituted cyclopropanes are also catalytically converted to alkenes (equation 8). Rhodium(II) ethanoate or [RhCl(CO)2]2 catalyze the reaction, but both catalysts form twice as much ( )- as (Z)-isomer. 

Okay. These are the reactions we want to happen, and they do happen somewhat as the byproducts of the engine leave the exhaust. The problem is that they don t happen all that quickly, leaving bad stuff heading out into the atmosphere. That s why we use catalysts that lower the activation energies for these reactions and help them proceed at a rapid rate. A catalytic converter is inserted in the exhaust system of a car so that it receives the bad stuff after it s left the engine. The catalytic converter contains a ceramic core coated with very expensive metals—platinum, rhodium, and palladium—and has two sections. The first section deals with nitrogen oxide and nitric oxide. 

Because of the complex nature of the reactions that take place in the converter, a mixture of catalysts is used. The most effective catalytic materials are transition metal oxides and noble metals such as palladium and platinum. A catalytic converter typically consists of platinum and rhodium particles deposited on a ceramic honeycomb, a configuration that maximizes the contact between the metal particles and the exhaust gases. In studies performed during the last ten years researchers at General Motors have shown that rhodium promotes the dissociation of NO molecules adsorbed on its surface, thereby enhancing the conversion of NO, a serious air pollutant, to N2, a natural component of pure air. 

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. 

Inside the catalytic converter is a porous ceramic structure with a surface coating of platinum and rhodium particles. 

FIGURE 18.16 (a) The arrangement of a catalytic converter used to reduce automobile pollution, (b) Cutaway views of several catalytic converters showing different structures for organizing metal catalysts, platinum, palladium, and rhodium on different substrates and supports. A steel-alloy heating element raises the temperature to 400 C in seconds, activating the catalysts and reducing the pollution emitted in the first minutes after the car is started. 

Clearly, the best catalyst for the reduction reactions may not be the best for the oxidation reactions, so two catalysts are combined. The noble metals, although expensive, are particularly useful. Typically, platinum and rhodium are deposited on a fine honeycomb mesh of alumina (AI2O3) to give a large surface area that increases the contact time of the exhaust gas with the catalysts. The platinum serves primarily as an oxidation catalyst and the rhodium as a reduction catalyst. Catalytic converters can be poisoned with certain metals that block their active sites and reduce their effectiveness. Because lead is one of the most serious such poisons, automobiles with catalytic converters must use unleaded fuel. 

Although TWC technology is now standard in the developed countries, effective implementation on a global scale is another story. World-wide annual production is more than 50 million cars, which, ideally should all be equipped with catalytic converters (which is not yet the case). This places great demands on the availability of noble metals, where rhodium is the critical and hence most expensive one. Regeneration of used catalysts is certainly possible but again needs to be implemented on a world-wide scale. 

Catalytic Converters Catalysts are used in the exhaust systems of cars and trucks to aid fuel combustion. The exhaust passes through the catalyst, often in the form of beads coated with metals such as platinum or rhodium. Catalysts speed the reactions that change incompletely burned substances that are harmful, such as carbon monoxide, into less harmful substances, such as carbon dioxide. 

One of the most widely known examples of catalyst poisoning is taken from the automobile industry. Though tetra-ethyl lead has been removed from essentially all gasoline in North America, the ban on leaded gasoline is not worldwide, and leaded and unleaded gasoline is available in many countries. Catalytic converters, which contain precious metals like platinum, palladium, and rhodium, are used to both reduce NO c and oxidize CO and unburned hydrocarbons. Lead irreversibly destroys the catalytic ability of the converter. Concentrations of lead in leaded gasoline are nominally 150mg/L. 

Catalytic Converters Catalytic converters on cars use the metals rhodium and platinum as catalysts to convert potentially dangerous exhaust gases to carbon dioxide, nitrogen, and water. Why don t cars need to have the rhodium and platinum replaced after they are used ... 

How a catalytic converter works A typical catalytic converter consists of particles of platinum and rhodium deposited on a ceramic structure that is like a honeycomb. The platimun and rhodium catalyze reactions that remove pollutants such as nitrogen monoxide (NO), carhon monoxide (CO), and unhurned hydrocarbons. When nitrogen monoxide binds to the rhodimn surface, it breaks down to oxygen and nitrogen. The bound oxygen reacts with carbon monoxide, which has also become bound to the rhodimn surface. The reaction produces carbon dioxide. The oxidation of unburned hydrocarbons produces carbon dioxide and water. 

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