DIRECT CONVERSION OF METHANE TO C-1 OXYGENATES OVER MOO3-USY ZEOLITES

Molybdena-containing ultrastable (USHY) zeolite has been prepared using different molybdenum precursors and activation procedures. The combined results of midinfrared, chemisorption of NO, and X-ray photoelectron spectroscopic measurements show that the zeolite structure is largely retained when the precursors are activated at temperatures as high as 773 K. It has been observed that for catalysts activated by a nonconventional procedure, which uses thermal decomposition under vacuum over long periods of time, a migration of the molybdena from the external zeolite surface into the lattice cavities occurs. These zeolites have been tested for the selective oxidation of methane using dioxygen as oxidant. The rate of methane conversion with this oxidant was found to depend on the MoO3 dispersion on the zeolite surface, whereas the selectivity toward formaldehyde as the major selective oxidation product seems to depend on the structure of the molybdena phase.