SSZ-13-supported manganese oxide catalysts for low temperature selective catalytic reduction of $$\hbox {NO}_{\mathrm{x}}$$ NO x by $$\hbox {NH}_{3}$$ NH 3

Abstract

A series of Mn/SSZ-13 catalysts of varying Mn content were synthesized by hydrothermal and co-precipitation methods. Their performances for the selective catalytic reduction (SCR) of $$\hbox {NO}_{\mathrm{x}}$$ with $$\hbox {NH}_{3}$$ were evaluated. The results indicate that over 95% $$\hbox {NO}_{\mathrm{x}}$$ conversion was achieved at a low temperature of $$150^{\circ }\hbox {C}$$ with an Mn loading of 4.74 wt%. Meanwhile, the $$\hbox {NO}_{\mathrm{x}}$$ conversion rate remained greater than 90% at $$450^{\circ }\hbox {C}$$ . The Mn/SSZ-13 catalysts were characterized by X-ray diffraction, ultraviolet–visible diffuse reflectance spectroscopy, Raman spectroscopy, transmission electron microscopy, $$\hbox {N}_{2}$$ -adsorption, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The analysis indicates that $$\hbox {Mn}_{2}\hbox {O}_{3}$$ , $$\hbox {Mn}_{3}\hbox {O}_{4}$$ , and amorphous $$\hbox {MnO}_{2}$$ coexist on the surface of the Mn/SSZ-13 catalysts, with $$\hbox {MnO}_{2}$$ comprising the largest proportion, which may contribute to the high SCR activity. Additionally, the specific surface area and pore volume both decrease with increasing Mn loading. The Mn/SSZ-13 catalyst with 4.74 wt% of Mn has a high concentration of lattice oxygen, a high amorphous $$\hbox {MnO}_{2}$$ content, and greatest number of strong Lewis acid sites, which are beneficial to the adsorption of $$\hbox {NH}_{3}$$ , and may account for its superior catalytic activity. SYNOPSIS Synthesis and characterization of Mn/SSZ-13 catalysts with varying Mn content by a hydrothermal and co-precipitation method are reported. Among the synthesized catalysts, Mn-SSZ-13-3 shows the best $$\hbox {NH}_{3}$$ -SCR, particularly at low temperature. Besides, the catalytic mechanism of Mn/SSZ-13 catalyst is reported.