Dual-bed catalytic system for NOx-N2O removal: a practical application forlean-burn deNO(x) HC-SCR

A dual-bed catalytic system has been developed by which NOx and N2O are suc cessively removed from flue gases, simulating lean-burn engine conditions. NOx is removed in the first stage by selective catalytic reduction with pro pene over a Pt supported on activated carbon catalyst. The second bed decom poses the N2O formed in the first bed into N-2 and O-2 Catalysts tested in this second stage comprise ex-Go-Rh,Al-HTlc and ex-Co,Pd-La,Al-HTlc mixed o xides derived from hydrotalcite-like compounds and ion-exchanged Fe-ZSM-5 a nd Pd -ZSM-5 zeolites. Variables studied for the most promising deN(2)O cat alysts are the effect of the pretreatment, the sodium content of the ex-HTl c-catalysts, the presence of inhibitors in the feed stream, the addition of hydrocarbons to enhance the N2O reduction in the second bed, and both time -on-stream and thermal stability of the catalytic system. Ex-Co-Rh,Al-HTlc proved to be the most active and stable catalyst, followed by Fe-ZSM-5, eve n when propene was added as reducing agent, which enhanced the conversion o ver the latter catalyst only. In an optimal configuration, at a temperature of 475 and 700 K in the first and second stage, respectively, molar conver sions of 90 and 100% for NOx and N2O were achieved in a stable operation du ring 50 h. (C) 2000 Elsevier Science B.V. All rights reserved.