On the structure of C 4 hydrocarbon species resulting from the adsorption of linear butenes on a Pt(111) surface as studied by thermal desorption and electron energy loss spectroscopies

Abstract

A combination of thermal desorption spectroscopy (TDS) and vibrational electron energy loss spectroscopy (EELS) has been used to study the compositions and structures of the species formed at different temperatures following the adsorption of 1-butene and the cis- and trans-2-butenes at 170 K on Pt(111). At this temperature each of the chemisorbed butenes gives a different EEL spectrum, corresponding to η 2 di-σ adsorbed species. At 300 K, the TDS evidence shows that the species from 1-butene has the empirical composition C 4H 7 and the EEL spectrum is consistent with the presence of an n-butylidyne structure. Cis- and trans-2-butenes give identical TDS spectra which define a composition of C 4H 6 at 300 K. Comparison with the spectrum from the adsorption of 2-butyne and the model cluster compound Os 3(CO) 10(CH 3CCCH 3) leads to the assignment of a μ 3−η 2 CH 3C:CCH 3 structure to the adsorbed species involving the central C:C bond in two σ-bonds and one π-bond to the metal surface. By 450 K virtually identical EEL spectra are obtained from all these linear butenes, and TDS implies a surface composition of C 4H 2.