Studies of the Ensemble Size Requirements for Ethylene Adsorption and Decomposition on pt(111): Ethylene and Bismuth Coadsorption

The coadsorption of bismuth and ethylene on Pt(111) has been studied by using AES, LEED, TPD, and HREELS. These studies were carried out to determine if bismuth acts as an inert, site-blocking agent that can be used to determine ensemble size requirements of ethylene adsorption and decomposition on Pt(111). These studies show that, indeed, bismuth has no effect on the heat of adsorption of molecular ethylene, the decomposition mechanism, or the activation energy required for C-H bond breaking or subsequent elementary decomposition reactions. The vibrational frequencies of adsorbed ethylene are also independent of bismuth coverage. Preliminary modeling of the decreased adsorption and reaction of ethylene due to coadsorbed bismuth determines that an ensemble of four Pt atoms is required for adsorption and a slightly larger ensemble (possibly five of six Pt atoms) is required for decomposition.