(616a) Operando XAS Characterization of Mn0.1CuxCo2.9-XO4 Direct NOx Decomposition Catalysts

Increasing automotive emissions regulations are driving the need for improved catalysts to mitigate production of oxides of nitrogen (NOx). While NO_x can be decomposed by adding excess reactants, the ability to mitigate NO_x catalytically without the addition of reactants can lead to higher efficiency combustion engines. Direct decomposition of NO to N₂ and O₂ is an ideal reductant-free solution; previous studies have investigated Cu-substituted, Co-based spinel catalysts (Cu_xCo_3-xO₄) for this application. Ex-situ studies have found a bulk structure-activity relationship in the Cu_xCo_3-xO₄ catalysts, showing that NO decomposition activity increases with Cu²⁺ incorporation into the spinel tetrahedral sites. Operando Cu K-edge XAS analysis has observed the generation of a linearly bound Cu¹⁺ species during pretreatment that was not identified in the ex-situ measurements. To further improve the Cu_xCo_3-xO₄ system, machine learning has been used to identify that adding Mn to the system would enhance NO conversion. To investigate the impact of the Mn dopant on the resultant structure and the change in the reaction product distribution of nitrogen containing compounds, operando K-edge XAS of Mn and Cu in Mn_0.1Cu_xCo_2.9-xO₄ catalysts were performed under NO decomposition reaction conditions with simultaneous product detection via mass spectrometry (MS). It was found that while the Mn K-edge shows subtle changes in coordination geometry during the pretreatment and NO reaction, the Cu K-edge shows evolution of Cu¹⁺ species in linear geometry, as seen in the Mn-free system. However, the inclusion of Mn seems to enhance the stability of linear Cu¹⁺ species under steady-state conditions. This structural feature can be correlated with NOx decomposition product distribution. The identification of structures involved in the formation of products over bulk oxide catalysts such as Mn_0.1Cu_xCo­O₄ through operando XAS characterization is expected to provide deeper insights into catalyst design and enhance direct NO decomposition activity.