The remote oxidation of soot separated by ash deposits via silver-ceria composite catalysts

One of the main issues of catalyzed diesel particulate filter is ash deposition onto catalyst coated on the filter. The effects of ash deposition on the catalysis of soot oxidation with gaseous oxygen were determined using multi-layered samples composed of a catalyst, an ash material and soot particles deposited on a thin cordierite plate in sequence. Catalysts composed of silver and ceria were used to enhance the oxidation of soot particles separated from the catalyst by ash deposits of either alumina or calcium sulfate. The effectiveness of remote soot oxidation was found to extend across an ash thickness of more than 50 mu m for both ash materials, although a catalyst composed only of ceria did not show any catalytic performance for remote soot oxidation. Using an O-18/O-16 isotopic exchange reaction and electron spin resonance techniques, a possible mechanism for this phenomenon was proposed, whereby a superoxide ion (O-2(-)) species generated on the catalyst surface first migrates to the ash surface and then to the soot particles, which it subsequently oxidizes. (C) 2014 Elsevier B.V. All rights reserved.