Carbon monoxide+ammonia coupling denitration at low temperatures over manganese–cerium/activated carbon catalysts

To identify the mechanism of the low-temperature CO + NH3 coupling selective catalytic reduction (SCR) denitration process, a series of Mn–Ce/activated carbon catalysts differing in the Ce content were prepared and characterized via SEM, EDS, XRD, XPS, FTIR and evaluated in the CO + NH3 coupling SCR denitration. The results show that the denitrification rates of Mn-Ce/AC catalysts are in the order of 7Mn-3Ce/AC > 7Mn-5Ce/AC > 7Mn-1Ce/AC at a temperature range of 150 °C–300 °C and an oxygen content of 9%. A moderate Ce content provides a smooth catalyst surface with a homogeneous distribution of metal particles and pores, resulting in the optimization of the physical and chemical performance of the Mn-based catalyst. As a result, more active oxygen species and lattice defects are formed, which promoted the dispersion of active components on the catalyst surface, increased the adsorption sites of CO and NH3, and provided more active sites for denitration reaction. Mn4+ and Ce3+ both increased to varying degrees, and oxygen-containing functional groups carboxyl and lactone groups increased, which promoted the synergistic reaction between MnCe, enhancing the NO adsorption and conversion rate. At 150 °C–250 °C, the CO + NH3 coupling denitration is mainly governed by physical adsorption, whereas chemical adsorption is the predominant mechanism at 250 °C–300 °C. The denitration process includes four stages: reaction gas adsorption, adsorption molecular dissociation, catalytic denitration of metal active components and product desorption.