IR spectra and the structures of the chemisorbed species resulting from the adsorption of the linear butenes on a Pt/SiO2 catalyst. Part 1.—Temperature dependence of the spectra

Abstract

The room-temperature adsorption of but-1-ene on a Pt/SiO₂ catalyst gives IR spectra which can be interpreted in terms of the presence of butylidyne and 1,2, di-σ surface species, together with π-bonded complexes. Heating to 100 °C leads to spectral changes interpreted as from the formation of —CH₂Pt groups at the expense of CH₃. Further heating leads to strong diminution of alkyl spectral features until only a broad alkene absorption at ca. 3060 cm^–1 remains at 300 °C.

Unlike the case of adsorption on Pt(111), where the spectra from the but-1-ene and but-2-enes differ markedly, on Pt/SiO₂ the spectra from all three butenes have a set of prominent common features which show the presence of butylidyne derived from but-1-ene. It is concluded that ready surface isomerisation in the form of double-bond migration occurs presumably on the rougher, non-(111), parts of the catalyst metal particles.