Environmental catalysts catalytic converters/exhaust

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%. 

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... 

Automobiles have a device called a catalytic converter. Its purpose is to promote a reaction by which noxious exhaust gases are changed to less environmentally harmful ones. What does this catalyst do to the activation energy ... 

In 2001 it was estimated that the world merchant market for catalysts was worth ca. US 25 billion, divided roughly equally between refining, petrochemicals, polymers, environmental (20-25% each) and with about 11% being used in fine chemicals. Refining is about the production of fuels (Chapter 3, Box 2), petrochemicals cover many of the basic commodity chemicals and the monomers required for the polymer industries fine chemicals include pharmaceuticals and agrochemicals, as well as flavours and fragrances and environmental is about exhaust gas and waste product clean-up. Vehicle catalytic converters use catalysts, as does the production of the main tonnage polymers polyethylene, polypropylene, polystyrene, polyvinyl chloride and polyethylene terephthalate. 

The platinum-group metals Rh, Pd and Pt play a vital role in keeping the environment devoid of pollutants originating from vehicle exhausts. They are present in catalytic converters (which we discuss in detail in Section 26.7) where they catalyse the conversion of hydrocarbon wastes, CO and NO c (see Box 14.8) to CO2, H2O and N2- The growth rate of environmental catalyst manufacture by companies... 

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. 

The platinum-group metals Rh, Pd and Pt play a vital role in keeping the environment devoid of pollutants originating from vehicle exhausts. They are present in catalytic converters (which we discuss in detail in Section 25.8) where they catalyse the conversion of hydrocarbon wastes, CO and NO. (see Box 15.7) to CO2, H2O and N2. In 2008, the manufacture of catalytic converters used 81% of the rhodium, 47% of palladium and 44% of platinum consumed worldwide. The growth rate of environmental catalyst manufacture by companies such as Johnson Matthey in the UK is driven by legislative measures for the control of exhaust emissions. Regulations in force in the US and Europe have had a major impact on the levels of emissions and have improved the quality of urban air. Tighter control of vehicle emissions has now been introduced in most parts of Asia. 

Selective catalytic reduction (SCR) is cmrently the most developed and widely applied FGT technology. In the SCR process, ammonia is used as a reducing agent to convert NO, to nitrogen in the presence of a catalyst in a converter upstream of the air heater. The catalyst is usually a mixture of titanium dioxide, vanadium pentoxide, and hmgsten trioxide. SCR can remove 60-90% of NO, from flue gases. Unfortunately, the process is very expensive (US 40- 80/kilowatt), and the associated ammonia injection results in an ammonia slip stream in the exhaust. In addition, there are safety and environmental concerns associated with anhydrous ammonia storage. 

The US Clean Air Act (CAA) of 1970 required that automobile exhaust emissions be regulated to meet new environmental standards. From 1975 all new models were to be fitted with catalytic combustion converters to reduce levels of carbon monoxide and unbumt hydrocarbons in the exhaust. This led to the phase-out of lead additives in gasoline between 1973 and 1996. To compensate for the loss of octane rating of the gasoline more reformate and alkylate needed to be added. Octane catalysts were also developed for FCC units and the aromat-... 

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