Oxygen Splitting and Methane Oxidation over Fe-Mordenite: Insight by the Operando 2D COS UV–Vis–NIR–IR Approach

Abstract

Activation of molecular oxygen and subsequent oxidation of methane over Fe sites in mordenite zeolites with different content of framework Al atoms were studied in the continuous regime at low temperatures. For this purpose, reactivity tests of methane oxidation by molecular oxygen over iron mordenite zeolites were combined with an operando 2D COS UV−vis−NIR−IR study to analyze the reaction pathway. The transmission spectra in the visible−NIR−IR range of investigated iron mordenites revealed the structural changes of Fe(II) after O 2 treatment and the formation of the spectral features typical for α-O stabilized on iron. Mass spectrometry analysis of gaseous products of the simultaneous interaction of methane and oxygen with iron mordenite revealed the formation of methanol, water, carbon monoxide, and carbon dioxide. Moreover, operando 2D COS UV−vis−NIR−IR also evidenced the presence of formaldehyde, formate, carbon dioxide, and carbon monoxide as products of subsequent methanol oxidation. The differences in the reaction pathway of methane oxidation over Fe-mordenite compared to Fe-ferrierite and Fe-*BEA catalysts reflect unique properties of mordenite topology providing isolated α-oxygens in individual mordenite pockets, although formed by splitting of molecular oxygen by two cooperating iron ions and the nature of adsorption sites in the mordenite matrix.