Insight into Enhancement of NO Reduction with Methane by Multifunctional Catalysis over a Mixture of Ce/HZSM-5 and CoO_<i>x</i> in Excess of Oxygen

Abstract

Selective catalytic reduction of NO by CH4 (CH4-SCR) is a promising choice to eliminate toxic NO from emissions of mobile and stationary sources. However, because of insufficient activity, so far a catalyst for CH4-SCR has not been used commercially. Getting a clear understanding of the mechanism of CH4-SCR is thus very important for developing an optimum catalyst for the NO elimination. From the angle of multifunctional catalysis, we designed a catalyst which consisted of CoOx and Ce/HZSM-5. With the synergistic function of the catalysis, the activity of CH4-SCR was considerably enhanced. In situ diffuse reflectance infrared Fourier transform spectroscopy was applied to investigate the catalytic mechanism of CH4-SCR. It suggests that CoOx offers the sites to boost the oxidation of NO to NOx. Meanwhile, Ce/HZSM-5 provides redox and acidic sites which are necessary for activating methane and reducing the formed intermediates into desired products, N2 and CO2.