The effect of NOx and CO on the rate of transition metal oxide catalyzed carbon black oxidation:: An exploratory study

The catalytic activity of Cr2O3, Co3O4, and CuD for the oxidation of carbon black in various gas compositions is reported. In 10% O-2 in Ar, the carbon black oxidation activity is improved considerably by intensifying the contact between the transition metal oxide (TMO) and carbon black by ball-milling (creation of 'tight contact') or impregnation, and also by increasing the surface area of the non-supported metal oxides. The effect of CO addition is strongly dependent on the catalyst: CO promotes the CuO catalyzed carbon black oxidation, it hardly affects the Cr2O3 activity, and inhibits the Co3O4 activity. Addition of NOx always enhances the catalytic carbon black oxidation rate. This is attributed to bifunctional catalysis: NO2 reacts with carbon black, yielding NO, CO acid CO2 and NO is reoxidized to NO2 over the TMO. NO improves the efficiency of the TMO by transportation of activated oxygen. In tight contact conditions the NO2/carbon black reaction might also be catalyzed. Catalytic filter configurations for the practical use of the NO2/carbon reaction over the investigated catalysts in diesel soot abatement are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.