Environmental Catalysts 1 Stationary Sources

Janssen, Environmental Catalysts - Stationary Sources, in Handbook of Heterogeneous Catalysis Vol. 4, Ed. by G. Ertl, H. Knozinger and J. Weitkamp, VCH Weinheim, 1997, p. 1633. 

It is fair to state that by and large the most important application of structured reactors is in environmental catalysis. The major applications are in automotive emission reduction. For diesel exhaust gases a complication is that it is overall oxidizing and contains soot. The three-way catalyst does not work under the conditions of the diesel exhaust gas. The cleaning of exhaust gas from stationary sources is also done in structured catalytic reactors. Important areas are reduction of NOv from power plants and the oxidation of volatile organic compounds (VOCs). Structured reactors also suggest themselves in synthesis gas production, for instance, in catalytic partial oxidation (CPO) of methane. 

The heterogeneous catalysts have a profound impact on the chemical industry in general for example 60% of all chemical processes, 75% of oil refining processes, nearly 100% of polymers and about one hundred petrochemicals depend on the action of catalysts, as well as a significant part of environmental technologies (VOCs, automotive emissions control, stationary sources, etc.) and fine chemical production. Actually, the worldwide catalysts market is worth about 10 billion USD, (i.e. 10 x 109 USD) a year and, according to some... 

This section on environmental catalysis highlights the development of catalysts for stationary sources. These are coal-, oil-, and gas-fired power plants, including gas turbines, waste incinerators, and gasifiers. 

In the preceding sections an overwiev is given of the application of catalysts in environmental technology, focusing on stationary sources. This last section overviews new developments in environmental catalysis and the challenges for fundamental... 

The emission of nitrogen oxides (NOx) from automotive and stationary sources causes serious environmental concern. Automotive exhaust gas aftertreatment systems are commonly based on precious metal catalysts (three way or diesel oxidation catalysts). One undesired effect during NOx reduction with these catalysts is the formation of N2O, which is now considered to be an environmental pollutant also [1,2], In this report the generation of N2 and N2O during NOx decomposition or reduction on Pt/alumina is investigated. 

Reactions involving the catalytic reduction of nitrogen oxides are of major environmental importance for the removal of toxic emissions from both stationary and automotive sources. As shown in this section electrochemical promotion can affect dramatically the performance of Rh, Pd and Pt catalysts (commonly used as exhaust catalysts) interfaced with YSZ, an O2 ion conductor. The main feature is strong electrophilic behaviour, i.e. enhanced rate and N2 selectivity behaviour with decreasing Uwr and , due to enhanced NO dissociation. 

Generally, catalysts are called into action to eliminate emissions from mobile (cars) and stationary (industry) sources, to take part in liquid and solid waste treatment, and contribute to the effort to reduce volatile organic compounds and gases that pose major environmental problems such as photochemical smog and (at a global level) the greenhouse effect. 

Tlie removal of NO from exliaust gases is an urgent issue, and environmental regulations are becoming more stringent tlian ever. The selective catalytic reduction (SCR) of NOx vvdth ammonia is the technique, which was extensively applied in stationary NOx sources from tlie 1970s, while the successful development of a three-way catalyst made it possible to reduce NOx in gasoline automobile exhaust. 

Particular attention is given to separation SO2 and NOx from power station exhausts. Environmental regulations pertaining to emissions from stationary fossil fueled power sources have focused on SO2 because it was implicated as an important component in acid deposition. Nitrogen oxides, including NO and NO2, have also been implicated as precursors to acid precipitation, whereas N2O is considered a potentially important greenhouse gas. Activated carbon is used as an adsorbent for the removal of SO2, and also as a catalyst for the reduction (and hence removal) of NOx from combustion flue gases. 

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