Exploration of the Mn-O coordination regulated reaction stability of manganese oxides in NH3-SCR: Effect of deposited ammonium nitrates

Abstract

Manganese oxide-based catalysts exhibit excellent low-temperature denitration efficiency, making them potential candidates for application. Herein, the relationship between reaction stability and phase structure for MnO2, Mn2O3 and Mn3O4 was disclosed. The NO conversion for Mn2O3 drastically reduced after 120 h reaction, while minor decline was detected for MnO2 and Mn3O4. Based on dedicate qualitative and quantitative analyses on the deposits over catalyst surface, deactivation trigged by ammonium nitrate (AN) deposition was confirmed. Different from penta-coordinated Mn4+ on MnO2 (110) and tri-coordinated Mn2+, penta-coordinated Mn4+ on Mn3O4 (101), the unique tetra-coordinated Mn3+ on Mn2O3 (200) could stabilize the nitrates and make it difficult to be removed via decomposition or reaction and accumulate continuously, which resulted in the significant deactivation. This research could not only unveil the poisoning mechanism of MnOx based catalysts, but also provide new insights into the relationship between the catalytic stability and surface Mn-O microstructure.