Abstract
Spent commercial Pd(Pt)/Al 2O 3 catalysts used in the elimination of hydrogen from carbon dioxide feed gas in the synthesis industry and deactivated by sulfur poisoning were characterized by chemical analysis, XPS, IR, XRD and TPR. The effect of the reaction conditions and the feed composition on the poisoning was examined. It was found that the sulfur in the poisoned catalysts exists in different chemical states, such as S 2-S 2- 2 and S 6+, owing to different reaction conditions (feed gas composition, reaction temperature, operated time, etc.). The negative charged sulfur ions exist essentially as noble metal sulfides on/in the surface of the catalysts. Under industrial reaction conditions, S 6+ is the main state of sulfur in the poisoned catalysts, and it combines with the carrier Al 2O 3 to form aluminium sulfate hydrate Al 2O 3-SO 3-H 2O with variable compositions. Furthermore, there are two kinds of SO 2- 4 with different toxicities to the catalysts. The mechanism of sulfur poisoning of Pd(Pt)/Al 2O 3 catalysts in H 2-O 2 reaction with different conditions was discussed.
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