OXIDATION OF METHANE TO FORMALDEHYDE BY NITROUS-OXIDE ON MECHANICALLY ACTIVATED MOLYBDENUM AND VANADIUM SILICATE CATALYSTS

A study was carried out on the effect of mechanochemical activation on the catalytic properties of Mo-, V-, and Fe-containing oxide systems supported on SiO2 (1) or their mechanical mixtures with SiO2 (2) in the oxidation of methane to formaldehyde. The mechanical activation of type-1 catalysts does not alter their activity and selectivity relative to the formation of formaldehyde. The conversion of methane to CO and CO2 on type-2 samples is reduced, while the selectivity relative to formaldehyde formation increases to 100%. X-ray diffraction analysis, electron microscopy, and Mossbauer and EPR spectroscopy were used to detect the formation of "capsules," namely, envelopment of particles of the active phase by silica gel accompanied by their chemical reaction, leading to change in the ratio of the active sites of the catalyst participating in the extensive and mild oxidation of methane.