Sulfur poisoning and regeneration of palladium-based catalysts. Part 2.—Influence of adsorbed sulfur on deactivation of carbonaceous deposits

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Abstract
The physicochemical and catalytic properties of palladium deposited on alumina and silica–alumina have been studied after poisoning by hydrogen sulfide as well as at various stages of regeneration under hydrogen. The amount of free palladium surface atoms was mainly deduced from infrared measurements of adsorbed carbon monoxide. The catalytic activity was measured in the cyclohexane dehydrogenation. As far as the steady-state activities are concerned, a regeneration under hydrogen between 673 and 773 K leads to samples having either the same activity (alumina support) or a higher activity (silica–alumina support) compared to that of the unpoisoned catalysts. Nevertheless, in both cases, the initial metallic surface was not recovered. Pulse experiments have been used for the determination of the initial activity. They showed that the deactivation by carbonaceous deposits is hindered when sulfur is present at the surface of palladium particles. Such deactivation is favoured when palladium is supported on an acidic carrier.