Application of HREELS to Model Catalysts: CO and C2H4 Adsorption on Pt/Al2O3

摘要

A model catalyst made by platinum vapor deposition onto a thin alumina film isinvestigated with Transmission Electron Microscopy and High Resolution Electron Energy Loss Spectroscopy. The preparation techniques are fully described, then the results of TEM analysis for platinum deposits from 0.3 monolayers to 1.7 monolayers are reported, for which clusters varying from 1.0 to 1.6 nanometers in diameter are observed. High Resolution Electron Energy Loss Spectroscopy spectra are reported for the cases of carbon monoxide and ethylene adsorption onto the model. For the case of CO adsorption, it is shown that the catalyst is stable when heated to 500 K. For the case of ethylene adsorption, pi and di-sigma species are identified for adsorption at 165 K, but on warming to 325 K, ethylidyne is only observed for the larger platinum deposits. This is first High Resolution Electron Energy Loss Spectroscopy observation of the ethylidyne species on alumina supported catalysts. Keywords: Platinum, Clusters, Catalysis, Aluminum oxide, Ethylene, Vibrational spectroscopy, High resolution electron energy, Loss spectroscopy, Adsorption, Carbon monoxide, Physical chemistry. (JG)