NO reduction by CH4 in the presence of excess O2 over Mn/sulfated zirconia catalysts

Selective catalytic reduction (SCR) of NO with methane in the presence of excess oxygen has been investigated over a series of Mn-loaded sulfated zirconia (SZ) catalysts. It was found that the Mn/SZ with a metal loading of 2–3 wt.% exhibited high activity for the NO reduction, and the maximum NO conversion over the Mn/SZ catalyst was higher than that over Mn/HZSM-5. NH3–TPD results of the catalysts showed that the sulfation process of the supports resulted in the generation of strong acid sites, which is essential for the SCR of NO with methane. On the other hand, the N2 adsorption and the H2–TPR of the catalysts demonstrated that the presence of the SO42− species promoted the dispersion of the metal species and made the Mn species less reducible. Such an increased dispersion of metal species suppressed the combustion reaction of CH4 by O2 and increased the selectivity towards NO. The Mn/SZ catalysts prepared by different methods exhibited similar activities in the SCR of NO with methane, indicating the importance of SO42−. The most attractive feature of the Mn/SZ catalysts was that they were more tolerant to water and SO2 poisoning than Mn/HZSM-5 catalysts and exhibited higher reversibility after removal of SO2.