Simultaneous catalytic removal of NO χ and diesel soot particulates over ternary AB 2O 4 spinel-type oxides

Abstract

Simultaneous removal of NO χ and diesel soot particulate in the presence of excess oxygen was investigated over ternary AB 2O 4 spinel oxides by using temperature programmed reaction (TPR) in which the soot/catalyst mixture was heated in the reaction gas containing nitric oxide and oxygen. The catalytic performance was evaluated by the ignition temperature of soot ( T ig) as a measure of activity, selectivity to nitrogen formation ( S N 2 C ) defined as a fraction of the charged soot used for nitrogen formation and selectivity to nitrous oxide ( S N 2 O = N 2 O N 2 + N 2 O . The catalytic performance depended significantly on constituent metal cations and CuFe 2O 4 was the most excellent catalyst with the highest ( S N 2 C lowest ( S N 2O and intermediate T ig. The comparison of catalytic performance of simple metal oxides, their mechanical mixtures and spinels in CuFe and CuCr systems revealed the appearance of synergetic effect in the S N 2 C enhancement by forming spinel structure. As for the activity and the selectivity to nitrous oxide, on the other hand, only the additive effect was observed. When a substantial amount of the charged soot remained in the soot/catalyst mixture and the effective area of the soot/catalyst contact was regarded as constant, Arrhenius plots of rates of carbon dioxide, nitrogen and nitrous oxide formation gave straight lines, suggesting that kinetic analysis of non-steady TPR results was possible. The compensation effect and good relation between S N 2 C and the apparent activation energy for nitrogen formation were found in the simultaneous NO χ-soot removal over spinel catalysts.