DEACTIVATION OF A PALLADIUM-SUPPORTED ALUMINA CATALYST BY HYDROGEN-SULFIDE DURING THE OXIDATION OF METHANE

A commercial Pd/Al2O3 catalyst was used to study its deactivation by hydrogen sulfide as a poison during the total catalytic oxidation of methane to carbon dioxide and water by small amounts of hydrogen sulfide in the feed. Experimental studies were carried out in a differential-type flow reactor. The reaction rate approach for the catalytic oxidation of methane results in a modified Langmuir-Hinshelwood-(Hougen-Watson-)type rate equation. Independent adsorption measurements of the individual components could be fitted best by Langmuir isotherms. The continuously added hydrogen sulfide caused a complete and practically irreversible deactivation of the catalyst. The chemical analysis of the unpoisoned and the completely poisoned catalyst was performed by X-ray photoelectron spectroscopy (XPS) with Mg Ka radiation (hv = 1253.6 eV) by monitoring the core level lines of Al2p, O1s, S2p, Pd3d, and C1s. We found palladium in its metallic ground state and sulfur in an oxidized form well above that of SO2, which is most likely identified with a SO3 and/or SO4 environment.