Formation of n-hexane from methylcyclopentane via a metallacyclobutane intermediate at step sites of Pt surfaces: Mechanism from first-principles calculations

With periodic density functional theory calculations, we examined the ring opening of methylcyclopentane to n-hexane via an αγ-adsorbed metallacyclobutane intermediate over the stepped model surface Pt(3 2 2). The crucial barrier of C–C scission along this pathway was calculated as low as 79 kJ mol−1, that is, about 20 kJ mol−1 lower than the value for analogous steps via ααββ-adsorbed intermediates on the way to 2- or 3-methylpentane on Pt(2 1 1). Thus, at step sites of Pt surfaces, formation of (unbranched) n-hexane seems to be more favorable than formation of branched hexanes.

Graphical abstractRing opening of methylcyclopentane via an αγ-adsorbed metallacyclobutane intermediate was studied computationally, yielding a barrier at step-edge sites as low as 79 kJ mol−1 on the way to n-hexane (nHx). Faster formation of nHx at steps yields a higher selectivity for nHx when the particle size decreases due to the larger ratio of step-to-terrace sites.Figure optionsDownload full-size imageDownload high-quality image (70 K)Download as PowerPoint slideHighlights► Ring opening of methylcyclopentane over Pt surfaces: a DFT-based mechanistic study. ► Lowest barrier to forming n-hexane via a metallacyclobutane intermediate at steps. ► n-Hexane selectively produced at steps. ► Smaller particles with relatively more steps yield higher selectivity to n-hexane.