REACTION-MECHANISM OF METHANE OXIDATION TO SYNTHESIS GAS OVER AN ACTIVATED PDY ZEOLITE

The catalytic behaviour of PdY zeolite has been investigated in the partial oxidation of CH4 into CO and H-2 under oxygen-deficient conditions. The PdY zeolite catalyst after reduction-reoxidation treatment showed excellent activity and selectivity in the temperature range 800-1000 K. Two possible pathways for the reaction were recognized from isothermal and temperature-programmed experiments, i.e. CO and H-2 are produced (1) on the oxidized surface by direct reaction between the surface oxygen and CH4 in the gas phase, and (2) on the reduced surface by the reforming of residual CH4 with primary-formed CO2 and/or H2O. It was confirmed by EXAFS analyses, furthermore, that under the operating conditions two kinds of Pd species (small clusters of Pd and PdO) coexist in the zeolite crystals and that they can function as catalytic sites via a reversible redox mechanism.