Effects of NO, NO2, CO and SO2 on NO oxidation over Pt/TiO2 for hybrid fast SCR process

Abstract

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 autoinhibition 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.

Effects of Cr on the NO oxidation over the ceria–zirconia solid solution

“…As part of NO is adsorbed as NO + , the ion pair NO + NO 3 2 can decompose to two NO 2 molecules, eqn (5). 32 At last, the Cr 3+ was oxidized to Cr 6+ again by Ce 4+ at high temperature, eqn (6). In order to verify the L-H model over 10Cr/Ce 0.5 Zr 0.5 O 2 catalyst, the kinetic test contained data of NO conversion versus different inlet concentrations of the NO and NO conversion versus different inlet concentrations of the O 2 were investigated.…”

“…1 Selective catalytic oxidation (SCO) method plays a decisive role in those main technologies of NO x decrease, such as NO x storage and reduction (NSR), 2,3 continuously regenerating trap (CRT) 4 and fast SCR. 5,6 What is more, some scientists bring up an amazing idea to reduce the emission of nitrogen oxides and sulfur dioxides at the same time in power plants. 7,8 This technology is a possible way to take place of SCR, which can avoid the high cost and possible corrosion of ammonia in SCR.…”