CO oxidation bistability diagrams for Pt/CeOx and Pt/SiO2 model catalysts prepared by electron-beam lithography

• The CO oxidation bistability diagrams (i.e., the interval of gas mixing ratio beta drop 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/CeOx 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, beta, between the three samples (at constant temperature). Simulations show that the experimental results can be understood by introducing an oxygen reactant supply via the CeOx, 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 CeOx, and the attachment across the Pt/CeOx interface have been estimated. The formation of a less reactive Pt state under oxidizing conditions is discussed. (C) 2001 Academic Press.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Nanoteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Nano-technology (hsv//eng)

Nyckelord

electron-beam lithography

Pt

CO oxidation

bistable reactions

kinetic phase transitions

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