Density Functional Study of Ethylene Hydrogenation on Pt(111) Surface

Abstract

The mechanism of ethylene hydrogenation on Pt surfaces has been investigated using the density functional method and the Ptn cluster models (n = 7, 10) modeling the Pt(111) surface. The energetics were investigated along the overall hydrogenation reactions: adsorption of ethylene onto the hydrogen preadsorbed Pt cluster, successive H atom migrations to adsorbed ethylene, and formation of ethane. Among the configurations considered here, the di-σ and π configurations gave the local minima. The di-σ configuration was found to be more stable than the π configuration for both the hydrogen free and preadsorbed surfaces. The calculated activation energy was larger for the second hydrogenation. Both the di-σ and π configurations lead to a common product, surface ethyl, from which the second hydrogenation occurs. The surface ethyl produced ethane in the eclipsed conformation, which was desorbed from the surface. Although the hydrogenation from the di-σ configuration is energetically favorable for clean surfaces, the energetics considerably depends on the coadsorbed surface species such as hydrogen atom and carbon deposit, and on the real catalysts, both reactions will proceed comparably.