Monomolecular alkane activation on Al-- and Fe--containing zeolites
Date
2014
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Zeolites are crystalline aluminosilicate materials with an open micro-porous three-dimensional framework structure and are used as a solid acid catalyst in oil refining and petrochemical industries, in processes such as fluidized catalytic cracking (FCC). FCC catalysts constitute more than 95% of zeolite catalyst consumption. Other zeolite-catalyzed processes include hydroxylation, alkylation, and epoxidation. Even though synthetic zeolites have been used in the industry for decades, prospects are still bright for recent new challenges and applications.
Synthetic and post-synthetic modifications of zeolites can be used in the improvement of catalysts; the modification of zeolites can lead to new catalytic chemistry.
In this thesis, we first investigated the effect of thermal treatments of SSZ-13 (CHA) with Si/Al ratios of 6 and 12 for the monomolecular propane conversion. SSZ-13 with Si/Al of 12 exhibited a gradual change in selectivity and activation energy with treatment temperature, indicating generation of different active sites.
Second, Fe3+ was isomorphously incorporated in the zeolite structure instead of Al3+ initially to compare the difference in acidity on alkane activation. A novel redox catalytic cycle was proposed and a mechanistic study with H-[Fe]ZSM-5 was explored to test the proposed mechanism.
In the next section, the monomolecular propane reaction is used again to investigate zeolites having only hydrogen-bonded acid sites. The constrained space leads to the formation of propyl cation intermediates predominantly, resulting in that the dehydrogenation pathway is favored than the cracking pathway.
In the last section of the thesis, the catalytic hydrodeoxygenation of furfural was examined using Ag-Cu bimetallic catalysts supported on SiO 2 . The selectivity indicates that hydrogenation rates are enhanced by the addition of Ag.
This thesis main contribution has been a redox catalytic cycle that can explain the catalytic properties of thermally treated and iron-silicate zeolites for alkane conversions. The results of catalytic reaction and the mechanistic investigation are consistent with the existence of redox chemistry in those zeolites. This new zeolite chemistry and its further application can contribute to the resolution of emerging challenges in a petrochemical industry with the recent rise of shale gas by, for example, helping in the on-purpose propene production.