A noble-metal-free SCR-LNT coupled catalytic system used for high-concentration NOx reduction under lean-burn condition

Abstract

A dual-bed fixed-bed reactor consisting of a selective catalytic reduction (SCR) catalyst and a lean NOx trap (LNT) catalyst is designed and employed for high-concentration NOx removal under lean-burn condition. The lean NOx could be partially reduced over the upstream SCR catalyst (Cu/Al2O3) by C3H6 in the stream, greatly increasing the efficiencies of both NOx storage and NOx reduction over the downstream LNT catalyst (La0.7Sr0.3CoO3). The activity tests for individual catalyst show that the Cu/Al2O3 containing 5 wt.% Cu is the optimal SCR catalyst, which exhibits similar temperature window of activity (300–350 °C) as the LNT catalyst La0.7Sr0.3CoO3. The relative ratio of CuO nanoparticles to surface CuAl2O4 spinel on Cu/Al2O3 is rather important for NO-SCR due to the requirements of appropriate oxidation ability of SCR catalysts. As compared with the single SCR or LNT catalyst, the dual-bed SCR-LNT coupled system shows much lower NOx leak in both lean- and rich-burn periods, especially under the condition of high NOx concentration and high space velocity. Additionally, the NOx to N2O selectivity over this coupled system is as low as ∼4%, showing obvious advantage over conventional noble metals-based SCR and LNT catalysts.