CO Oxidation Bistability Diagrams for Pt/CeO_x and Pt/SiO₂ Model Catalysts Prepared by Electron-Beam Lithography

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• 作者：Johansson ; Stefan ; Ö ; sterlund ; Lars ; Kasemo ; Bengt
• 关键词：electron-beam lithography ; Pt ; CO oxidation ; bistable reactions ; kinetic phase transitions
• 刊名：Journal of Catalysis
• 出版年：2001
• 期刊代码：97_00219517
• 类别：ce
• 出版时间：July 25, 2001
• 卷：201
• 期：2
• 页码：275-285
• 文件大小：246 K

摘要

The CO oxidation bistability diagrams (i.e., the interval of gas mixing ratio β≡P_CO/(P_CO+P_O2) vs temperature for which a bistability exists) have been determined for different electron beam lithography (EBL) fabricated supported model catalysts. Three different samples were studied, one Pt/SiO₂ sample and two Pt/CeO_x samples, where the support type, particle size, and interface length were varied independently. The kinetic bistability is an inherent property of the CO oxidation on Pt at certain gas mixtures and temperatures, and we find that the actual position of the bistable region is a very sensitive tool to measure differences in reaction kinetics on different samples. The bistable region is shifted considerably along the gas mixing ratio axis, β, between the three samples (at constant temperature). Simulations show that the experimental results can be understood by introducing an oxygen reactant supply via the CeO_x support (spillover), which does not exist for SiO₂. This extra supply of oxygen will maintain a high CO conversion rate up to higher relative CO partial pressures on ceria samples (by suppressing the CO poisoning effect). Energy barriers for O diffusion on CeO_x and the attachment across the Pt/CeO_x interface have been estimated. The formation of a less reactive Pt state under oxidizing conditions is discussed.