Methane selective oxidation to formaldehyde with Fe-catalysts supported on silica or incorporated into the support

The selective oxidation of methane to formaldehyde was performed on iron (0.1–0.5 wt%) catalysts supported on silica prepared by the sol–gel method with (“Fe-dissolved”) or without (“Fe-precipitated”) pH control. SEM and TEM permits to differentiate the preparation methods which lead to a homogeneous composition sample or to the formation of iron isolated species, respectively. The Mössbauer analyses confirm the higher metal dispersion with pH control method. The catalytic activity was carried out between 400 and 750 °C. The “Fe-precipitated” catalysts display higher methane conversion but selectivity towards methanol, whereas the “Fe-dissolved” catalyst leads to the maximum formaldehyde yield.