(172f) Design of Ni-Based Intermetallic Compounds to Promote C–H Bond Cleavage and Control C–C/C=C Bond Activation in the Dehydrogenation of Light Hydrocarbons

Authors: 
He, Y., University of Tennessee
Song, Y., University of Tennessee
Laursen, S., University of Tennessee
Non-noble metal intermetallic compounds (IMCs) composed of atomically ordered mixtures of transition metals (TM) and post-transition metal or semimetal elements provide a large compositional space that can be utilized to tune the surface chemistry towards C–H, C–C, and C–O bonds of various saturations that is of significant interest to the greater heterogeneous catalysis community. Production of unsaturated hydrocarbons (olefins and aromatics) and their use as chemical building blocks form a significant portion of the foundation of the chemicals industry. However, the unusual balance of reactivity between the product and reactant leads to considerable challenges in controlling catalyst selectivity while still achieving appreciable conversion. Utilizing a dehydrogenation reaction (i.e. propane to propylene), we have investigated the innate surface chemistry of a suit of IMCs in promoting C–H activation while simultaneously limiting C=C or C–C activation, hydrogenation, and coke formation. The most selective catalyst that also showed appreciable activity consisted of a Ni+Ga composition with tailored IMC surface composition. The catalyst presented appreciable stability towards olefin production with only moderate deactivation detected after extended operation (total olefin selectivity began at ~95% and fell to only 93% after a 82+ hr run) at 600℃. The catalyst also exhibited the ability to be regenerated easily with oxidative and reductive treatments using only O2 and H2. Synthesis methods were designed such that a single IMC phase was promoted regardless of the nominal loading of Ni and Ga. This feature allowed control of the IMC surface composition and insights into the tunability of the surface and catalytic chemistry of the materials. The investigations of mechanistics and electronic structure over Ni+Ga catalysts using quantum chemical modeling calculations indicated that the surface reactivity can be systematically tuned by manipulating the electronic structure within the solids, which correlated well with our experimental observations.
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