SIMULTANEOUS CATALYTIC REMOVAL OF NOX AND DIESEL SOOT PARTICULATES OVER TERNARY AB(2)O(4) SPINEL-TYPE OXIDES

Simultaneous removal of NOx and diesel soot particulate in the presenc e of excess oxygen was investigated over ternary AB(2)O(4) spinel oxid es by using temperature programmed reaction (TPR) in which the soot/ca talyst mixture was heated in the reaction gas containing nitric oxide and oxygen, The catalytic performance was evaluated by the ignition te mperature of soot (T-ig) as a measure of activity, selectivity to nitr ogen formation (S-N2/C) defined as a fraction of the charged soot used for nitrogen formation and selectivity to nitrous oxide (S-N2O = N2O/ N-2 + N2O). The catalytic performance depended significantly on consti tuent metal cations and CuFe2O4 was the most excellent catalyst with t he highest S-N2/C, lowest S-N2O and intermediate T-ig. The comparison of catalytic performance of simple metal oxides, their mechanical mixt ures and spinels in Cu-Fe and Cu-Cr systems revealed the appearance of synergetic effect in the S-N2/C enhancement by forming spinel structu re, As for the activity and the selectivity to nitrous oxide, on the o ther hand, only the additive effect was observed, When a substantial a mount of the charged soot remained in the soot/catalyst mixture and th e effective area of the soot/catalyst contact was regarded as constant , Arrhenius plots of rates of carbon dioxide, nitrogen and nitrous oxi de formation gave straight lines, suggesting that kinetic analysis of non-steady TPR results was possible, The compensation effect and good relation between S-N2/C and the apparent activation energy for nitroge n formation were found in the simultaneous NOx-soot removal over spine l catalysts.