LanguageTerm (authority = ISO 639-3:2007); (type = text)
English
Abstract (type = abstract)
The 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.
Subject (authority = local)
Topic
Pincer
Subject (authority = RUETD)
Topic
Chemistry and Chemical Biology
RelatedItem (type = host)
TitleInfo
Title
Rutgers University Electronic Theses and Dissertations
I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.