Adsorption and dehydrogenation of ethane on a silica-supported platinum catalyst monitored in the temperature range 90–294 K by FTIR spectroscopy

Abstract

FTIR spectroscopy has been applied to study the adsorption and dehydrogenation of ethane on a silica-supported platinum (Pt/SiO₂) catalyst with metal particles diameters mostly in the range 5–15 nm and with predominantly [111] micro-facets. At ca. 90 K, there is clear spectroscopic evidence for the formation of a first monolayer of di-σ C₂H₄ species on the platinum particles, overlaid with a multilayer of ethane. On warming towards room temperature the multilayer gradually evaporates into the gas phase, and from ca. 130 K the di-σ C₂H₄ species transforms to ethylidyne, reaching saturation by 294 K. As the di-σ C₂H₄ to ethylidyne transformation is well known to occur on [111] surfaces, and as dissociation of ethane is not observed to occur on a single crystal Pt[111] surface at low temperature, it seems that the initial dissociation on the finely divided Pt/SiO₂ catalyst occurs on non-[111] sites, followed by migration to the [111] facets.