Effect of morphology on the performance of MnOx catalysts for selective catalytic reduction of NO with NH3

Abstract

Modulating the physicochemical properties of catalysts through the construction of special crystal structures or microscopic morphology provides new insights for developing high-performance low-temperature denitrification catalysts. This paper explores the effect of morphology structure on catalyst performance and identifies the dominant driving factors. The catalyst activity sequence was found to be MnOx spiny nanospheres (Mn-SNS) > MnOx nanowires (Mn-N) > MnOx nanospheres (Mn-NS) > MnOx nanoparticles (Mn-P). Among these, the Mn-SNS catalyst prepared by the hydrothermal method exhibited the best catalytic activity and the good resistance to water and sulfur. It achieved over 70% NOx conversion at 150 °C, and maintained 100% at 200–350 °C. In the presence of SO2 and H2O, the NOx conversion was maintained at 87%. The spherical structure consisting of nanospikes provides the Mn-SNS catalysts with a large specific surface area, more (Mn4++Mn3+), abundant acid sites, and stronger reducibility, thus exhibiting excellent performance through the "fast-SCR" pathway. It also inhibits oxide crystallization and provides more sites for the adsorption activation of NOx and NH3. The nanowire structures can provide a large specific surface area and a high concentration of Mn3+ and Mn4+ for MnOx catalyst. Characterization analyses revealed that the specific surface area, the ratio of (Mn4++Mn3+)/Mn, and the number of Lewis acid sites (L-NH3) are the most important factors affecting the catalytic activity. This present empirical analysis provides new ideas for designing high-performance catalysts with a large specific surface area.