Infrared spectroscopic comparison of the chemisorbed species from ethene, propene, but-1-ene and cis- and trans-but-2-ene on Pt(111) and on a platinum/silica catalyst

Abstract

The chemisorption of ethene, propene, but-1-ene, cisand trans-but-2-ene and but-2-yne has been studied on a Pt(ll1) surface using reflection absorption infrared spectroscopy (RAIRS). The results have been compared with transmission infrared spectra of the alkenes adsorbed on a finely divided impregnated Pt/Si02 catalyst.On the Pt(ll1) surface ethene, propene and but-1-ene are adsorbed in the corresponding n-alkylidyne form CH,(CH,),CPt, (n = 0, 1, 2) at room temperature. The cisand trans-but-2-enes are adsorbed in the form of but-2-yne bonded to the surface in a di-o/x fashion, as was confirmed by adsorption of but-2-yne itself.The room-temperature spectra of ethene, propene and but-1-ene on Pt/SiO, all exhibited prominent absorptions from the n-alkylidyne, but other adsorbed species also contributed to the spectra, considered to be predominantly the appropriate di-o species PtCH,CH(R)Pt (R = H, CH, , C, H, ) together with smaller amounts of the relevant n-complexes. In the case of the cis-and trans-but-2-enes, virtually identical spectra were obtained on Pt/Si02 but with many of the same prominent features as from but-1-ene. Clearly the finely divided catalyst had sites which led to double-bond isomerization. A smaller proportion of di-o/n bonded but-2-yne was also present.The infrared spectra proved to be very effective at delineating the similarities and differences between the species chemisorbed on Pt(ll1) and on the Pt/SiO, catalyst.

An infrared spectroscopic study of 2-methylpropene (isobutene) adsorbed on a Pt/SiO2 catalyst before and after hydrogenation

“…ene, adsorbed on Pt/Si02 (2). The latter results were comExperimental pared with those obtained by reflection-absorption infrared…”

The chemistry of simple alkyl species on Pt(111) generated by hyperthermal collisions

“…The gaseous CH 4 was then formed by recombinative desorption of CH 3 and H, while ethene was believed formed primarily by CH 2 addition coupled with ␤-hydride elimination ͑CH 2 ϩCH 3 →C 2 H 5 →C 2 H 4 ϩH͒. By comparison with rather limited literature relating to adsorbed ethyl fragments 3,6,10,12,13,16 and with the literature RAIRS data on the propylidyne moiety ͑wCCH 2 CH 3 ͒ which is in effect an ethyl group removed from the surface by insertion of a carbon atom, 35 we can confidently assign these features to the C-C and CH 2 ͑i.e., the CH 2 wag͒ modes, respectively, of the ethyl moiety. On the Pt͑111͒ surface, Zaera et al 15 report that adsorbed CH 3 generated by thermal decomposition of methyl iodide underwent either hydrogenation to form gas phase CH 4 or dehydrogenation to form surface carbon.…”

Self-assembling of InAs nanocrystals on GaAs: The effect of electronic coupling and embedded gold nanoparticles on the photoluminescence

“…We attribute this absorption band to a CH 2 twist and rock vibrational mode associated with the organic linker. 15 This mode is not active in the IR, in the case of adsorbed organic monolayer. However, the attachment of the InAs NPs breaks the symmetry of the system and induces its IR activity.…”