The recent boom in unconventional oil recovery has led to an increase in hydrocarbon feed stocks, among which are included the lighter C2-C5 compounds that currently find only limited commercial use. Activating and upgrading such shorter alkanes to longer chain alkanes via tandem-catalyzed reactions such as alkane-metathesis and alkane-dimerization would allow for generation of hydrocarbon feedstocks for fuels. In this context, pincer-ligated iridium complexes in homogeneous batch experiments are known to be effective in synthesizing olefins from the parent alkanes, oftentimes with observed terminal olefin regioselectivity. Immobilizing such catalysts would allow for their easier handling, recyclability, and use in systems incorporating other catalysts such as zeolites or olefin metathesis catalysts. In this work, we introduce a continuous-flow reactor system for analyzing analogous gas-phase dehydrogenation reactions with precise control over residence time and other reaction variables such as temperature and reagent partial pressure. Supported catalysts of the form [SiO2]-O-(R4PXCXP)Ir(C2H4) (R = iPr, tBu; X = CH2, O) are synthesized via incipient wetness impregnation and the kinetics of catalyzed acceptorless dehydrogenation are explored in detail. The supported complexes are shown to have higher efficiency in dehydrogenation when activated under a reducing atmosphere, indicative of strong olefin binding which is also responsible for inhibition in the course of attempted alkane transfer dehydrogenation. Tandem reactions are effected with a mixture of supported Pincer-Ir catalyst and zeolite/olefin-metathesis catalyst and system selectivity is quantified as a function of various reaction variables such as temperature, catalyst ratio and residence time.

Investigating the kinetics of supported, Pincer-ligated iridium catalysts in a continuous-flow gas phase system for C4 upgrading

255th National Meeting (2018)

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