The selective catalytic reduction (SCR) rate of NO with N-containing reducing agents can be enhanced considerably by converting
part of NO into NO
2. The enhanced reaction rate is more pronounced even at lower temperatures by using an equimolar mixture of NO and NO
2 (fast SCR reaction). The oxidation characteristics of NO over catalyst Pt/TiO
2 have been determined in a fixed bed reactor (8 mm-ID) with different concentrations of oxygen, nitric oxide and nitrogen
dioxide in the presence of 8% water. The conversion of NO to NO
2 increases with increasing oxygen (O
2) concentration from 3 to 12%, but it levels off at higher O
2 concentrations. The NO conversion to NO
2 decreases with increasing NO concentration and it also decreases by an addition of NO
2 in the feed stream. Therefore, the oxidation of NO over Pt/TiO
2 catalyst could be auto-inhibited by the reaction product of NO
2. The effects of CO and SO
2 on NO oxidation characteristics have also been determined. In fact, the presence of SO
2 significantly suppresses oxidation of NO but due to the less stability of sulfate on anatase structure in TiO
2, it becomes less significant. On the other hand, the presence of CO increases NO oxidation significantly due to the auto-inhibition
effect by CO. Moreover, the effect of SO
2/CO on NO oxidation has also been determined and it was observed that NO oxidation decreases with the increase in SO
2/CO ratio.
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