Hydrophobic Mn/ZSM-5 modification for highly efficient O₃ decomposition under humidity conditions

The competitive adsorption of water molecules in practical environments typically leads to severe deactivation of ozone (O₃) decomposition catalysts. In this study, a series of x-Mn/ZSM-5 catalysts were successfully prepared through the organic functionalization method to enhance moisture resistance. The O₃ conversion over the x-Mn/ZSM-5 catalysts exhibited a distinct volcanic trend as a function of the carbon chain length of the various alkylsilanes. Specifically, the C4-Mn/ZSM-5 catalyst modified with butyltriethoxysilane (C4) demonstrated outstanding activity, maintaining over 85% O₃ conversion for 6 h even at 80% relative humidity (RH). The comprehensive characterization revealed that the organosilanes reacted with the hydroxyl groups (Brønsted acid sites (SiOHAl, SiOH, and MnOH) of Mn/ZSM-5 to form siloxane bonds, thereby significantly enhancing surface hydrophobicity. This modification not only modulates the coordination environment around MnO_x species, but also facilitates the formation of low-valence Mn species accompanied by abundant oxygen vacancies (V_o). Density functional theory (DFT) calculations confirmed that both MnOH sites and V_o serve as active centers for O₃ removal. Moreover, the MnOH species possess a remarkably lower energy barrier for the rate-determining step (0.704 eV) compared to V_o (0.842 eV). The coexistence of MnOH sites and V_o accelerates O₃ decomposition. The synergistic effect between optimal hydrophobicity through organic functional groups and the rapid Mn²⁺/Mn³⁺ ↔ Mn⁴⁺ redox cycling over the C4-Mn/ZSM-5 catalyst is crucial for the efficient O₃ catalytic elimination in high RH environments.