Development, characterization and application of silica-supported pincer-iridium catalysts for heterogeneous, continuous-flow alkane valorization
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Sheludko, Boris.
Development, characterization and application of silica-supported pincer-iridium catalysts for heterogeneous, continuous-flow alkane valorization. Retrieved from
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TitleDevelopment, characterization and application of silica-supported pincer-iridium catalysts for heterogeneous, continuous-flow alkane valorization
Date Created2020
Other Date2020-10 (degree)
Extent1 online resource (xxviii, 202 pages) : illustrations
DescriptionThe production of olefins from alkanes is one of the most valuable industrial transformations currently in use, as hundreds of millions of tons of olefins are used globally per year to generate plastics, fuels and specialty chemicals. While most light olefins are obtained via high-temperature cracking processes, there has been recent interest in “on-purpose” alkane dehydrogenation. Pincer-iridium complexes of the form [(R4PCP)Ir] (R4PCP = κ3-C6H3-2,6-(XPR2)2; X = CH2, O; R = tBu, iPr), having been studied for several decades, are highly efficient and often regioselective alkane molecular dehydrogenation catalysts. The development of a system incorporating the active site of these materials into a heterogeneous catalyst could potentially be valuable and industrially applicable.
In this work, such pincer-iridium species are immobilized on an amorphous silica support and the resultant materials are studied in a continuous gas-flow reactor to characterize their structure, thermal stability and kinetic properties. In chapter 3, the stability of these immobilized complexes is explored, and it is shown that immobilization increases the maximum temperature of stability from 240 °C to 300-340 °C, likely by eliminating bimolecular decomposition pathways. In chapter 4, in situ diffuse reflectance Fourier-transform IR spectroscopy is used to monitor the iridium speciation under reaction conditions. Carbon monoxide is shown to stabilize the catalyst against decomposition at elevated temperatures, likely by mitigating interaction of the iridium center with the silica support. Chapter 5 explores the behavior of such immobilized pincer iridium species under alkane transfer dehydrogenation conditions, and an effect on regioselectivity is observed that is dependent both on the nature and partial pressure of the olefinic sacrificial hydrogen acceptor. The resulting regioselectivity is explained via a model previously calculated via DFT for molecular species, supporting the fact that the active site remains unchanged upon immobilization. In chapter 6, the decomposition product of the immobilized pincer-iridium complex (tBu2PO-tBu4POCOP)Ir(L) (L = C2H4, CO) is shown to be a novel iridium phosphide nanophase via XAS, NMR and IR, that is stable against agglomeration on the silica surface and is an efficient alkane dehydrogenation catalyst as well.
NotePh.D.
NoteIncludes bibliographical references
Genretheses, ETD doctoral
LanguageEnglish
CollectionSchool of Graduate Studies Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.
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