Experimental Study on Soot Oxidation Characterization of Pt/CeO ₂ Catalyst with NO and O ₂ Using a Flow Reactor System

The oxidation of soot (carbon black) which is assisted by Pt/CeO₂ catalyst is studied using a flow reactor system simulating the condition of diesel exhaust. In this study, the temperature programmed oxidation (TPO) scheme is mainly used for different NO and O₂ concentrations and soot oxidation rate is evaluated by monitoring both CO and CO₂ concentrations.

Pt/CeO₂ catalyst lowers the temperature of the peak CO/CO₂ concentrations significantly when there is either NO or O₂. Oxidation starts at 200°C and the peak CO₂ concentration is observed at 360°C, which depends on the amount of catalyst and NO concentration.

The effect of catalyst on NO₂ recycling is also investigated. For this purpose, two different types of sample have been prepared. For the mixed case, 10mg of carbon black is mixed with 50mg of Pt/CeO₂ catalyst under conditions of loose contact. For the unmixed case, the catalyst layer is placed on top of soot layer without mixing. In the mixed case compared to the unmixed one, the temperature for the peak CO/CO₂ concentrations is decreased from 400°C to 370°C and a significant increase of specific reaction rate is observed around 360°C. This result indicates that mixing soot and catalyst enhances NO-NO₂ conversion which takes place a couple of times while the NO molecule passes through the sample mixture and supports the fact that the soot oxidation rate depends upon the amount of NO₂ produced by NO-NO₂ conversion.