Catalytic Technology for Soot and Gaseous Pollution Control

AbstractIn this chapter, stationary and automotive technologies for gaseous and particulate pollution abatement are discussed. Stationary pollution abatement technologies involve the reduction of NOxemissions from the exhaust gases of power plants, industrial boilers, and gas turbines, and are based on selective catalytic reduction (SCR) using ammonia. In automotive pollution control, internal combustion engines represent the major source for the emission of NOx, CO, and unburned hydrocarbons (HCs), whereas diesel engines contribute to the emission of soot and NOx. These gaseous pollutants can be minimized with primary measures, for example, modification of the combustion process, and with additional secondary measures (exhaust purification by catalysts). The most frequent type of catalytic converter in automobiles is the three‐way catalyst (TWC) in stoichiometric operated gasoline engines, which simultaneously converts NOx, CO, and HCs. NOxemissions from lean‐operated enginescanbe removed by urea‐SCR and NOxstorage reduction catalysts (NSC). Catalytic CO oxidation is an essential reaction of the TWC and NSC, and is also applied in diesel engines using the diesel oxidation catalyst (DOC) that can oxidize gaseous HCs as well as HCs adsorbed onto soot particles. Diesel particulate filters (DPFs) are used to remove soot from diesel exhaust by filtration of the particles through the porous walls of the filter. The DPF application requires regeneration; that is, oxidation of the stored soot particles, which is accomplished by indirect (NO2‐assisted) and direct (redox metal oxide‐based) catalytic oxidation of the accumulated soot particles in the DPF.