Preparation method and structure of active sites of FeOx/SiO2 catalysts in methane to formaldehyde selective oxidation

The effects of preparation method on surface structures and catalytic properties in the selective oxidation of CH4 to HCHO with O2 (MPO) of low-loaded (0.09–0.43 wt.% Fe) FeOx/SiO2 catalysts have been addressed. The DR-UV-Vis patterns prove that the preparation route, based on “adsorption–precipitation” of FeII precursors on silica under anaerobic conditions (ADS/PRC), enhances the dispersion of the active phase in comparison to the conventional “incipient-wetness” route. FTIR of adsorbed NO data signal the presence on silica of several “isolated” Fe moieties with a different surface coordination. A higher FeOx dispersion confers a superior performance to ADS/PRC FeOx/SiO2 catalysts in terms of specific rate of CH4 conversion (σCH4) and HCHO formation (εHCHO) of Fe atoms which result in quite larger HCHO productivity values (STYHCHO).