The Thermal Chemistry of 1-Chloro-3-Iodopropane (ClC₃H₆I) Adsorbed on Pt(111)

Abstract

HREELS and XPS indicate negligible dissociation of ClC3H6I during adsorption at 100 K. During TPD, no ClC3H6I desorbs for coverages below 0.4 ML. For higher, but not multilayer coverages, parent ClC3H6I desorption occurs in two peaks, 200 and 230 K. After even larger doses, unsaturable multilayer desorption occurs at 170 K. HREELS indicates that most C−I bonds dissociate by 205 K. The following reaction paths are proposed on the basis of TPD and HREELS results. When the C−I bond breaks, 3-chloropropyl fragments, C(a)H2CH2CH2Cl, are formed and these either lose HCl to form η3- or η-allyl or lose a β-hydrogen to form 3-chloro-di-σ-propylene. Some η3-allyl groups hydrogenate to either propylene, some of which desorbs at 240 K, or n-propyl, some of which hydrogenates to release propane at 250 K. Other η3-allyl groups isomerize to η1-allyl. At 250 K, 3-chloro-di-σ-propylene eliminates chlorine as HCl and also releases H atoms that hydrogenate neighboring C3 fragments. The η1-allyl fragment either hydrogenates and desorbs as propylene at 325 K or isomerizes to propylidyne. Propyl and di-σ-propylene moieties rearrange to form propylidyne or release propylene at 325 K. Interestingly, there is some benzene desorbing at 375 K. To account for it, a diene metallacycle is suggested. Atomic iodine desorbs at 825 K. Comparisons of the thermal chemistry of ClC3H6I on Ag(111) and Ni(100) are made as are comparisons of ClC3H6I with other C3 adsorbates on Pt(111).

The surface chemistry of hydrocarbon fragments on transition metals: towards understanding catalytic processes

“…It has also been determined that the alkyl chains initially orient themselves flat on the surface in order to maximize their interaction with the metal, but reorient to a perpendicular configuration with higher tion instead [52]. Finally, the activation of chemisorbed halohydrocarbon precursors has been extended successfully to the production of surface carbenes [53-561, vinyls [57, 581, allyls [59][60][61][62], metallacycles [63][64][65][66][67], and oxametallacycles [68, 691.…”

Chlorine-Modified Properties of Ag(111) Probed by C2H4, C3H6, C3H5Cl, and CO

“…Turning to adsorbate selection, describing the surface chemistry of C 3 hydrocarbon species on transition metals continues to be a significant thrust of our work, − particularly unsaturated C 3 hydrocarbons. C 3 species are small enough to be tractable experimentally while at the same time requiring consideration of the richness associated with multiple energetically accessible isomers, features not at issue for C 1 and, to some degree, C 2 hydrocarbons.…”

Surface Chemistry of 1- and 3-Hexyne on Pt(111): Desorption, Decomposition, and Dehydrocyclization

“…For the alkynes, an additional mechanistic route without the formation of an alkene species could lead to the formation of an allylic intermediate, namely, half-hydrogenation to a vinyl-intermediate followed by a 1,2-hydrogen shift. These isomerizations caused by hydrogen shifts have been observed for several hydrocarbons on Pt(111), including the interconversion between adsorbed acetylene and vinylidene and η 3 -allyl to propylidyne . The formation of a hexadiene species is followed by additional dehydrogenation steps leading to hexatriene, which finally forms benzene.…”

“…These isomerizations caused by hydrogen shifts have been observed for several hydrocarbons on Pt(111), including the interconversion between adsorbed acetylene and vinylidene 51 and η 3 -allyl to propylidyne. 52 The formation of a hexadiene species is followed by additional dehydrogenation steps leading to hexatriene, which finally forms benzene. The proposed reaction mechanism is summarized in Figure 7.…”