Enhanced activity and water resistance of hierarchical flower-like Mn-Co binary oxides for ammonia-SCR reaction at low temperature

Abstract

Manganese-based catalysts applied for selective catalytic reduction of NOx with ammonia (NH3-SCR) still exist certain drawbacks, including narrow operating window, weak water resistance and low selectivity. A number of novel Mn-Co binary oxides with hierarchical flower morphology are synthesized through solvothermal to boost the catalytic performance and H2O tolerance. The formation of the hierarchical flower morphology with high specific surface area could provide short diffusion channels and accessible adsorption sites for NH3 and NO species. Moreover, strong interaction between Mn and Co oxides endows the catalyst with enhanced Lewis acid sites, which could preferentially adsorb NH3 species than H2O. Therefore, the catalyst Mn-Co-F (1:1) presents superior activity with NOx conversion and N2 selectivity > 80% within 60–320 °C, together with remarkable water resistance of 99% NOx conversion under the condition of 15 vol% H2O. The reaction process over Mn-Co-F catalyst follows Langmuir-Hinshelwood mechanism below 200 °C and Eley-Rideal mechanism above 200 °C, respectively. This study creates a unique route for designing high-efficiency Mn-based catalysts used for the NH3-SCR process.