Abstract
The process of carbon deposition on Pt/Al 2O 3 and Pt–Sn/Al 2O 3 catalysts under different conditions was investigated in a multifunctional apparatus which can be used for hydrogen chemisorption, TPO and TPSR determinations. The results showed that on both Pt and Pt–Sn catalysts, carbon deposition is a dynamic process. The carbonaceous materials which originate from the metal surface may be converted to carbon through successive dehydrogenation on metal sites, or they may continuously migrate to the support with irreversible coke formation through condensation or hydrogen transfer reactions. The results of chemisorption and thermal desorption of ethylene on platinum and platinum-tin catalysts showed that the incorporation of tin reduced the strength of chemisorption of the hydrocarbons on the metal surface, so that the carbon precursors can migrate towards the support more easily. The proportion of carbon deposited on the support of the platinum-tin catalysts was greater than that of the platinum catalysts. With the same level of carbon deposition, 30% of the metal surface on platinum-tin catalyst remained uncovered, whereas only 10% of the metal surface of the platinum catalysts was bare. The high stability of Pt-Sn/Al 2O 3 catalysts is closely related to the larger bare metal surface under high-temperature conditions.
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