On the catalytic nature of Mn/sulfated zirconia for selective reduction of NO with methane

In this work, the catalytic nature of Mn loaded sulfated zirconia (SZ) catalysts for the selective catalytic reduction (SCR) of NO with methane was investigated by a combination of reactions and characterizations such as FT-IR spectroscopy, H2-TPR, UV–vis diffuse reflectance spectroscopy (DRS) and NO-TPD. It was found from the results of reactions and FT-IR spectra that the strong Brønsted and Lewis acid sites in the Mn/SZ catalysts were essential for the SCR of NO with methane. The loading of Mn increased the number of strong Lewis acid sites on the surface of SZ catalyst, which is one reason for its promoting effect. On the other hand, FT-IR spectra, H2-TPR and UV–vis DRS of the catalysts demonstrated that the presence of the SO42− species occupied the terminal OH sites on the surface of ZrO2 support and thereby restrained the formation of more oxidative and nonstoichiometrically dispersed MnOx (1.5 < x < 2) phase. Such an effect of SO42− suppressed the combustion reaction of CH4 by O2 and increased the selectivity towards NO reduction. The NO-TPD showed that the loading of Mn increased the adsorption of NO over SZ catalyst, which is another reason for the promoting effect of Mn.