Studies of Catalyst Degradation in Automotive Emission Control Systems

Reactions of sulfur, present in small amounts in gasoline, with catalyst and catalyst support materials are discussed.

GMR studies have shown that sulfur accumulates in catalysts and support materials at temperatures of 600-1300 F under both oxidizing and reducing conditions. Partial sulfur release has been observed at 1200-1600 F.

Concurrent with sulfur accumulation, there is a marked reduction in the carbon monoxide (CO) reactivity of noble metal, promoted and base metal catalysts. Lesser highly variable effects on hydrocarbon (HC) reactivity were noted. Studies of nitrogen oxide (NO_x) reducing, noble metal catalysts also showed an adverse effect of sulfur accumulation on the NO_x reactivity.

These results indicate that steps must be taken to reduce or eliminate sulfur poisoning of automotive emission control systems. Approaches for achieving this objective are discussed.