Spectroscopic Characterization of Vinyl Formed from Acetylene on Pt(111)

Abstract

The surface intermediates formed following the adsorption of acetylene (C 2 H 2 ) on Pt(111) were identified and characterized with reflection absorption infrared spectroscopy (RAIRS). It is found that isomerization of acetylene to vinylidene (CCH 2 ), followed by hydrogenation to vinyl (CHCH 2 ), precedes the formation of ethylidyne (CCH 3 ). When hydrogen and acetylene are coadsorbed on the surface, di-σ-bonded ethylene (C 2 H 4 ) and vinyl (CHCH 2 ) intermediates form at about 250 K. Vinyl is identified by its CH 2 symmetric stretch at 2988 cm -1 and CC stretch at 1280 cm -1 . The isomerization of acetylene is indicated by the formation of only one vinyl isotopomer, CDCH 2 , from the reaction of surface deuterium with C 2 H 2 . Vinyl converts to ethylidene, ethylidyne, and a high-temperature form of vinylidene at temperatures above 300 K. Ethylidyne isotopomers formed from H/D exchange when C 2 D 2 is adsorbed on the H preadsorbed surface and when C 2 H 2 is adsorbed on the D preadsorbed surface are identified by their RAIR spectra.

Ethylene adsorption and oxidation on Pt(h k l) in acidic media

“…This fact suggests that there exists a strong interaction of the C@C double bond of the vinylidene species with the metal surface, what results in a decrease of the C@C bond order, as pointed before. This would support the configuration of l 3 -g 2 -C@CH 2 , as it was observed by Deng et al [45]. This adsorbed form of vinylidene has its C@C double bond tilted to the surface by about 40°allowing the interaction between the adsorbate p-electrons with the surface.…”

“…This is the situation for vinyl and vinylidene species [3,5]. The identification of vinyl and vinylidene as intermediate adsorbates during ethyne hydrogenation has been reported in several studies in UHV [4,[41][42][43][44][45][46] for different transition metal surfaces. These species have been identified by means of infrared [4,45] and electron energy loss (EELS) [41,43,46] spectroscopies.…”

“…The identification of vinyl and vinylidene as intermediate adsorbates during ethyne hydrogenation has been reported in several studies in UHV [4,[41][42][43][44][45][46] for different transition metal surfaces. These species have been identified by means of infrared [4,45] and electron energy loss (EELS) [41,43,46] spectroscopies. The assignment of the bands was done by comparison with the corresponding spectra of coordination compounds of vinyl and vinylidene species with ruthenium and osmium [47][48][49].…”

“…If we assume that the tilted angle varies respect to the direction perpendicular to the metal surface from 40° [ 45] at the lowest potential with a frequency of 1554 cm À1 to an angle of 0°with a frequency of 1640 cm À1 , corresponding to l-vinylidene, and if we accept that (C@C) stretching vibrations in both vinylidene species would have a similar extinction coefficient, we obtain the graph plotted in Fig. 10.…”

Adsorption and decomposition of γ-butyrolactone on Pd(111) and Pt(111)

“…For the g 1 g 2 species, the expected vibrational modes would involve only C-C, C-H, and C-H 2 groups. Deng et al reported only two vibrational modes for RAIR spectra of a vinyl intermediate on Pt (1 1 1), at 1280 cm À1 (m(CC)) and at 2988 cm À1 (m-s(CH 2 )), [30] while a vinyl HREEL spectrum on Pt(1 1 1) by Hsiao et al yielded several modes, at 2980 (ma(CH)), 1450 (m(C@C)), 1400 (v(CH 2 )), 1255 (q(CH 2 )), 930 (x(CH 2 )), 870 and 770 cm À1 (d(CH)) [31]. Many of the modes for the GBL-derived intermediate in the present work (see Table 2) agree reasonably well, at 2972, 1440, 1388, 1202, 934, 896, and 777 cm À1 .…”