Selective Catalytic Reduction of NOx with Methane over Ag-alumina Catalysts in High-content SO2 Gas Streams

In this work, we investigated the performance of Ag-alumina catalysts for the SCR of NO with methane in gas streams with a high concentration of SO2, typical of coal-fired power plant flue gas. Agalumina catalysts were prepared by co-gelation and nitric-acid leaching was used to remove weakly bound silver species from the catalyst surface [1, 2]. We found that SO2 has a dramatic inhibitory effect on these catalysts, essentially quenching the SCR reaction at T <600C. At temperatures higher than 600C, the CH4-SCR of NO occurs without catalyst deactivation even in 1000 ppm SO2, the SO2 effect was reversible, and quick activity recovery was observed after removal of SO2 (Fig.1). Further, coaddition of water vapor (6.2%) does not change the above findings. Fig. 1 SCR of NO with CH4 over sulfated AlAg(7.2,L). Sulfation: 0.25%NO-2%CH4-5%O2-2000ppm SO2-He, 625C, 24h. Catalyst: 0.1027g. Feed gas: 0.25%NO-2%CH4-5%O2-0/1000ppm SO2He, 200ml/min. T=625C. SV = 72,000h. At low temperatures, SO2 adsorbs strongly on the catalyst surface forming sulfates on both alumina and silver. We determined that sulfates are not active for CH4-SCR of NOx. The reaction light0 20 40 60 80 100 0 10 20 30 40 50 Time (h) C on ve rs io n of N O to N 2 ,C H 4 t o