Roles of Acidic\nProton for Fe-Containing Zeolite in\nDirect Oxidation of Methane

Fe-containing zeolite catalysts are active in N<sub>2</sub>O decomposition\nand direct oxidation of unreactive methane. Except for the well-known\nability that acid sites realize the subsequent reaction of methanol\nto hydrocarbon, the roles of acidic protons in the direct oxidation\nof methane have not been studied regarding the formation of active\nFe components and the reactivity in the reaction. Herein, on the premise\nof the comparable total Fe and Al contents, the acidity of one-pot\nsynthesized Fe-AEI and ion-exchanged Fe/AEI zeolites was adjusted\nby various Na contents, and the catalytic activity in methane oxidation\nreactions was compared under different conditions. Ultraviolet–visible\n(UV–vis) spectra at 25–500 °C of the as-synthesized\nFe-AEI and the reaction performance at the corresponding conditions\nwere combined to clarify the formation of potential active Fe species.\nAcidic proton was favorable for the formation of potential active\nFe species for the one-pot synthesized Fe-AEI zeolite. However, for\nthe H-type Fe/AEI zeolite, thermal treatment at high temperatures\nwas prone to dealuminate, reduced the number of anchors for Fe<sup>3+</sup> attachment, and resulted in inactive Fe<sub><i>x</i></sub>O<sub><i>y</i></sub>. Furthermore, in contrast to\nthe robust N<sub>2</sub>O adsorption capacity of Na<sup>+</sup>, the\nacidic proton exhibited weak competition with Fe<sup>3+</sup> for\nN<sub>2</sub>O adsorption and thus contributed to the higher activity\nin the methane oxidation reaction. Our findings highlighted the importance\nof the acidic proton for the formation of potential active Fe species,\nthe frail competition of adsorption N<sub>2</sub>O with Fe species,\nand the feasibility of the tandem reaction of methane to methanol\nand methanol to hydrocarbon.