The relationship between the structural and surface characteristics of catalysts based on molybdenum oxide and the selectivity of these catalysts in the partial oxidation of methane is investigated. Among the issues addressed are the nature of active sites, the effects of promoters, catalyst- support interactions, the role of lattice oxygen, and the participation of the gas-phase oxidant. Supported, unsupported, and promoted catalysts are prepared and characterized using laser Raman spectroscopy, X-ray diffraction, scanning electron microscopy with three- dimensional imaging, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, steady-state kinetics, and transient response experiments. The role of lattice oxygen in the oxidation reaction is examined using in situ laser Raman spectroscopy in conjunction with isotopic labelling. Methane is readily available from natural gas or refinery effluents. Its direct partial oxidation to methanol or formaldehyde would offer major savings in both capital and operating costs over traditional methods of making these products. Molybdenum-oxide catalysts show promise for this conversion, but further study is needed to obtain a practical process.
