等离子体协助InZSM-5选择性催化还原贫燃NO_x

Research on Lean NO_x Removal by Plasma Enhanced Selective Catalytic Reduction over InZSM-5

为了解等离子体协助选择性催化还原(SCR)贫燃NOx的效果及相关因素,以NO模拟尾气中NOx,C2H4为还原剂,InZSM-5为催化剂,空速为32000h-1,试验研究了NO/O2/N2/C2H4系统中,单独等离子体、单独SCR及等离子体协助SCR 3种技术路线下NOx的去除率,并考察了等离子体电压、电源频率及空速对NOx去除的影响。试验发现:单独等离子体作用时NOx无法被有效的还原成N2,但等离子体在一定电压下可显著提高CH-SCR活性;较低空速下,等离子体协助InZSM-5效果明显提高;在2.5-4 kHz内,电源频率对等离子体协助SCR影响不大。

Because traditional three-way catalysts （TWC） can＇t reduce NOx efficiently in excess oxygen, researchers have paid more attention to lean NOx removal at home and abroad, and plasma enhanced selective catalytic reduction （plasma-SCR） was considered as a promising way to achieve NOx control. In this paper, the two-stage plasma-enhanced SCR system, which meant that plasma reator was separated from catalytic reactor, was selected, and the relationships between plasma discharge voltage, frequency, GHSV and NOx removal rate, the selectity of NO to NO2 were studied carefully. The experimental apparatus included gas control system, ac power source with high frequency, dielectric barrier discharge （DBD） reactor, catalytic reactor and analysis instruments. NO, O2 and Nx were simulated the exhaust gas, and C2H4 was added into the manifold as reductant. InZSM-5 containing 3%In（wt） was prepared as catalyst. Plasma only, catalysis only and plasma enhanced SCR were conducted respectively to compare the removal rate of NO.. The results showed that plasma could oxidate NO into NO2 efficiently, and most of NO. was converted into other N-contalning compounds instead of N2 under higher plasma voltage when plasma alone. These N-containing products would be oxidated or reducted to NOx again over catalyst. After plasma proceeded, HCHO, CH3NO3, CO and other intermediates were produced, which would greatly influence the performance of NO. removal in catalysis stage. Plasma could effectively improve NO, removal rate when combined with SCR, which relied on plasma voltage significantly. At the same time, the effects of GHSV in catalytic stage and frequency of power supply were both investigated in the experiments. It was found that lower GHSV benefited for NO, removal, while the frequency didn＇t represent prominent influence in the range from 2. 5kHz to 4kHz.