Constructed electron-dense Mn sites in nitrogen-doped Mn3O4 for efficient catalytic ozonation of pyrazines: Degradation and odor elimination

In this study, N-doped Mn₃O₄ catalysts (Mn-nN) with electron-dense Mn sites were synthesized and employed in heterogeneous catalytic ozonation (HCO). These catalysts demonstrated excellent performance in pyrazines degradation and odor elimination. The synthesis of Mn-nN was achieved through a facile urea-assisted heat treatment method. Experimental characterization and theoretical analyses revealed that the MnN structures in Mn-nN, played a crucial role in facilitating the formation of electron-dense Mn sites that served as the primary active sites for ozone activation. In particular, Mn-1N exhibited excellent performance in the HCO system, demonstrating the highest 2,5-dimethylpyrazine (2,5-DMP) degradation efficiency. ^•OH was confirmed as the primary reactive oxygen species involved in the HCO process. The second-order rate constants for 2,5-DMP degradation with O₃ and ^•OH, were determined to be (3.75 ± 0.018) × 10⁻¹ and (6.29 ± 0.844) × 10⁹ M⁻¹ s⁻¹, respectively. Seventeen intermediates were identified through GC-MS analysis during the degradation of 2,5-DMP via HCO process with Mn-1N. The degradation pathways were subsequently proposed by considering these identified intermediates. This study introduces a novel approach to synthesize N-doped Mn₃O₄ catalysts and demonstrates their efficacy in HCO for the degradation of pyrazines and the elimination of associated odors. The results show that the catalysts are promising for addressing odor-related environmental issues and provide valuable insights about the broader significance of catalytic ozonation processes.