MCM-41-supported iron phosphate catalyst for partial oxidation of methane to oxygenates with oxygen and nitrous oxide

Iron phosphate supported on MCM-41 has been studied for partial oxidation of methane with both oxygen and nitrous oxide. Characterizations with XRD, Raman spectroscopy, XPS, and H₂-TPR suggest that the supported iron phosphate species with loading amounts lower than 40 wt% are located and dispersed in the mesopores of MCM-41. Such iron phosphate species can be reduced more readily than the unsupported iron phosphate at lower temperatures. Methane is selectively converted to methanol, formaldehyde, and dimethyl ether over the supported and the unsupported iron phosphate with nitrous oxide at milder temperatures (300-500°C), while formaldehyde is mainly produced along with carbon oxides with oxygen at relatively higher temperatures (400-600°C). The supporting of iron phosphate onto MCM-41 with loading amounts of ca. 20-40 wt% increases both methane conversion and overall selectivity to useful oxygenates with either oxygen or nitrous oxide. Kinetic studies indicate that the activation of oxygen occurs rapidly, while the activation of nitrous oxide proceeds at a comparable rate with the conversion of methane by the active oxygen species over both the supported and the unsupported catalysts. The supported catalyst, however, enhances the activation of nitrous oxide and thus remarkably inhibits the carbon deposition occurring over the unsupported iron phosphate.