jp0724830_si_001.pdf (3.34 MB)
Infrared Spectroscopy Characterization of the Chemistry of C4 Hydrocarbons on Pt(111) Single-Crystal Surfaces
journal contribution
posted on 2007-07-12, 00:00 authored by Ilkeun Lee, Francisco ZaeraThe uptake and thermal chemistry of a number of C4 hydrocarbons on Pt(111) single-crystal surfaces were
characterized by reflection−absorption infrared spectroscopy (RAIRS). The compounds studied include butane,
1-butene, cis-2-butene, trans-2-butene, and 1,3-butadiene as well as 1-iodobutane, 2-iodobutane, 1-bromo-2-butene, and 1-bromo-3-butene, precursors for the formation of corresponding alkyl and alkenyl intermediates.
Much of the chemistry reported here agrees with previous work on similar systems, and conforms with the
general idea of hydrogenation, dehydrogenation, and H−D exchange reactions occurring by single hydrogen
incorporation and elimination steps according to the so-called Horiuti Polanyi mechanism. In addition, though,
a couple of surprising observations are presented of particular relevance to the mechanism of carbon−carbon
double bond isomerizations. In particular, it was seen that although the isomerization of trans- to cis-2-butene is more favorable and occurs at lower temperatures than the reverse cis-to-trans conversion, β-hydride
elimination from the common 2-alkyl intermediate produces trans-2-butene preferentially. This indicates that
it is the relative adsorption energy of the alkene what determines selectivity in these reactions.