CATALYTIC COMBUSTION OF METHANE OVER PALLADIUM SUPPORTED ON ALUMINA AND SILICA IN PRESENCE OF HYDROGEN-SULFIDE

The catalytic combustion of methane is Performed over palladium suppor ted on alumina and silica in Presence or not of hydrogen sulfide. In t he case of alumina, a treatment at 873 K under the sulfur-free mixture leads to an increase in the catalytic activity. The activation is ins tantaneous in the case of silica. The presence of sulfur strongly deac tivates both solids and the extent of deactivation is independent on t he support. However, the alumina support lowers the rate of deactivati on because of the trapping of sulfate species. In the case of the sili ca support infrared spectroscopy shows that the poisoning species woul d be a sulfate group bonded to the palladium surface atoms; in additio n, this technique allows to determine the variations of the amount of sulfur deposited after poisoning and after thermal treatment. The exte nt of regeneration under nitrogen and hydrogen is correlated with the stability of the poisoning species.