The recent boom in unconventional oil recovery has led to an increase in hydrocarbon feed stocks, among which are included the lighter C<sub>6</sub>- compounds which currently find only limited commercial use.  Being able to convert these to longer chain compounds would allow them to be included in transportation fuels.  One way to effect this transformation is via tandem alkane transfer dehydrogenation (AXD) - olefin metathesis, with the dehydrogenation step being performed by a pincer-ligated iridium catalyst and the metathesis by a metathesis catalyst such as rhenium(VII) oxide. Prior work has demonstrated that AXD can be performed with several such iridium catalysts in batch homogeneous and heterogeneous reactions; However, in order for this process to find expanded use in industrial-scale applications, a continuous-flow system is preferred.<br/>            In this work, we use such a system to investigate the activity of immobilized pincer-ligated iridium catalysts for AXD.  The catalysts are immobilized on a solid support (γ-alumina, mesoporous silica), and reactions are carried out with an air-free plug-flow reactor. Catalyst activities toward AXD and rate dependencies on reagent partial pressures are measured, and activation energies are determined in order to provide support for a proposed heterogeneous AXD mechanism. <br/>We study the effect catalyst binding mode has on activity, demonstrating that catalysts that have a free iridium(I) center in the supported state retain activity toward AXD, in contrast to those that oxidatively add surface hydroxyl groups to generate iridium(III).  The latter catalysts are shown to be efficient hydrogenation catalysts; Other supported iridium(III) catalysts of the form (POCOP)Ir(H)(X) are also investigated and shown to be effective for olefin hydrogenation with high turnover frequencies.

Continuous-flow heterogeneous alkane transfer dehydrogenation catalyzed by immobilized pincer-ligated iridium complexes

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.