Fabricating M/Al₂O₃/cordierite (M = Cr, Mn, Fe, Co, Ni and Cu) monolithic catalysts for ethyl acetate efficient oxidation: Unveiling the role of water vapor and reaction mechanism

The reduction and control of VOCs from anthropogenic sources becomes a research hotspot due to their tremendous environment hazards. Fabricating efficient and applicable noble-metal-free monolithic catalysts is still a great challenge for industrial VOC economical removal. In this work, cordierite-based honeycomb monolithic catalysts (M/Al₂O₃/COR; M = Cr, Mn, Fe, Co, Ni and Cu) were synthesized by a versatile and scalable wash-coating method and adopted for ethyl acetate (EA) catalytic oxidation. Mn/Al₂O₃/COR possesses remarkable activity with 90% of ethyl acetate (EA) oxidized at 236 °C owing to abundant surface active oxygen species. Moreover, excellent stability and water resistance of Mn/Al₂O₃/COR were observed during long-term successive reaction. In situ DRIFTS results reveal that the decomposition of EA to ethanol is the main pathway under humid conditions, and the presence of low content water vapor (≤1 vol%) promotes EA conversion ascribed to the presence of abundant OH derived from H₂O dissociation; however, further increasing of water concentration inhibits EA conversion. The adsorption of OH over oxygen vacancies inhibits the generation of surface oxygen species and blocks further oxidation of intermediates to form acetate, leading to the reduction of CO₂ yield and formation of coke aggregates. This work will provide instructive and feasible references for designing of VOC oxidation catalysts under practical reaction conditions.