The Study Of Selective Catalytic Reduction Of NO By CH₄ In Combination Of Non-thermal Plasma And Catalysts

The removal of nitrogen oxides (NOx) has attracted world-wide attention due to the serious threat for human health and environment. For a long time, Selective catalytic reduction (SCR) of NO by hydrocarbons has been studied as a potential method to remove NOx from exhaust gases. But one challenge for HC-SCR is that the effective temperature window is relatively narrow and the reaction temperature is too high. Non-thermal plasma technology can active molecular at low temperature and catalytic reaction has the virtue of high selectivity. Thus using plasma as an aid to HC-SCR can remove NOx more effectively. The main results have been summarized as follows:1. In pure plasma reaction, input power is a main factor to NOx conversion. However, reaction temperature has little influnce. When using plasma-assisted catalyst system, the conversion of NO and CH4 improve a lot, indicating that synergistic effect occurs between the plasma and the catalyst. The NOx conversion is much higher than the sum of plasma alone and catalyst alone.2. The CH4-SCR of NO was studied in combination of plasma and catalyst. Among the series of metal oxides as catalysts,γ-Al2O3 exerts the best activity. At 300℃and the discharge power of 4.5 W, the NOx conversion reaches 56.5% in the combination of plasma withγ-Al2O3, much higher than that in pure plasma mode (28.9%). At this temperature, no conversion of NO or CH4 was observed in pure catalytic reaction withγ-Al2O3 as the catalyst, further indicating a synergistic function between the plasma and the catalyst. In the plasma-assisted catalyst reaction, the porous structure and surface acidity of the catalyst obviously promote the CH4-SCR of NO.3. The effect of the combination way of plasma and catalyst was investigated. One-stage mode is more favorable for NO reduction than two-stage mode. Because in one-stage mode, the catalyst embedded in a phase rich in radicals and other activated species produced by plasma and can take advantage of these species. Thus, synergetic effects occurs.4. Silver catalysts were investigated in plasma-assisted NO reduction. Alumina-supported silver catalyst shows much lower activity than alumina. However, titanium dioxide-supported silver catalyst is more effective than Titanium dioxide. Titanium dioxide is a well-known photocatalyst, and Ag/TiO2 may can be activated by high-energetic electrons and photons produced by plasma. So it performs better than TiO2 in NOx reduction.