The influence of CO 2 on NO reduction into N 2 over reduced ceria-based catalyst

Oxygen defects in reduced ceria are the catalytic sites for the NO reduction into N 2 in the Toyota Di-Air DeNO x abatement technology. Traces of NO (several hundred ppm) have to compete with the excess amount of other oxidants, e.g., 5% CO 2 and 5% O 2 , in an exhaust gas of a lean burn (diesel) engine. The reactivities of CO 2 and NO over a reduced ceria and noble metal loaded reduced ceria have been investigated under ultra-high vacuum system in TAP and under atmosphere pressure in in-situ Raman and flow reactor set-up. The results showed that CO 2 was a mild oxidant which was able to oxidise the oxygen defects, but hardly oxidised deposited carbon over both ceria and noble metal loaded ceria. NO was a stronger oxidant and more efficient in refilling the oxygen defects and able to convert the deposited carbon, which acted as buffer reductant to extend the NO reduction time interval. NO was selectively and completely converted into N 2 . The presence of excess CO 2 hardly affected the NO reduction process into N 2 .