Soot Oxidation in Particulate Filter Regeneration

Junko UCHISAWA, Akira OBUCHI and Tetsuya NANBA  

This chapter deals with the mechanism of soot oxidation for the regeneration of particulate filters. Nature of catalysts and effect of process parameters (temperature, NO2 partial pressure, intimacy of contact between soot and catalyst,. ..) are reviewed. The role of oxygen mobility and of nature of oxygen species are also discussed. 

Most of the PM mass from diesel engines ranges from 0.1 to 0.5 xm in diameter, which is much less than the suspended particulate matter (SPM) standard prescribed in the Air Quality Standards of Japan (10 xm or less), and the PM2.5 (2.5 p,m or less) standard prescrihed hy the United States Environmental Agency. To make matters worse, the majority of PM is made up of ultrafine particles with diameters of 0.005-0.1 xm. Ultrafine particles of 0.05 xm or smaller are called nanoparticles, and these cause concern with regard to invasion of respiratory organs such as bronchial tubes, alveolar eells, and further Wood vessels, and are thus detrimental to human health.  

Junko Uchisawa, Akira Obuchi and Tetsuya Nanba 

From the 1980s to early 2000s, control of PM was mainly accomplished using technologies that improved engine combustion, most successfully with the common-rail system, i.e., an electronically controlled high-pressure fuel injection system. However, as more severe emission regulations have been enforced worldwide, the adoption of after-treatment systems that directly remove exhausted PM has become inevitable. 

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Some other filter regeneration strategies are under investigation, such as modifications of the CRT systems that incorporate active phases in the filter instead of, or in addition to, that in the previous oxidation catalyst or the Toyota Motors DPNR (diesel particulate NO reduction) system for the simultaneous removal of NO and soot. 

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