Abstract:
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The hydrogenation of triple and double
carbon−carbon bonds in C4 molecules containing a single
unsaturation has been investigated for the lowest index
surfaces of the triad Ni, Pd, and Pt through first-principles
simulations. Both low and high hydrogen coverage have been
explored to identify the nature of the selectivity found in the
experiments. The adsorption behavior of the alkynes and
alkenes at high hydrogen concentrations differs from the
structures in the infinite dilution-limit coverage which makes a
significant contribution to selectivity. Structure sensitivity is
also a consequence of the hydrogen coverage, at high contents
(111) surfaces cannot trap the C4 molecules efficiently, and
thus, the reactivity mainly occurs on the more open (100) surfaces. The combination of fast/slow elementary steps, crucial to
eliminate trans-alkenes that are health threatening, is not possible for any of the metals studied, although some metals present
slightly better behavior. Our study paves the way towards an integrative analysis of the hydrogenation process that accounts for
high surface coverage, preferential adsorption, and kinetic contributions. |