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Nanoscale confined biomimetic catalysts : synthesis, characterization and catalysis

Authors Zhan, Bi-Zeng
Issue Date 1998
Summary This thesis focuses on the development of novel "ship-in-a-bottle" systems with the main aim at the preparation, characterization and catalysis of the efficient and industrially viable biomimetic catalysts. Two types of zeolites are synthesized around transition metallocomplexes by either "build-bottle-around-ship" or "assemble-ship-inside- bottle" approach. Nanoscale confined metalloporphyrins exhibit very exciting catalytic activity in the hydroxylation of alkanes and arenes, epoxidation of unfunctionalized alkenes, hydrogenation of alkenes, and hydrolysis of nitriles. Chapter 1 outlines the main objectives of biomimetic chemistry of metalloporphyrins in mimicking cytochrome P-450 enzymes. Previous works on zeolite encapsulated transition metal complexes, including phthalocyanines, 2,2'-bipyridine, and other diamine complexes, mainly synthesized by "assemble-ship-inside-bottle" method, are summarized. Chapter 2 presents our development of "build-bottle-around-ship" method to synthesize faujasite-Y (NaY) confined chromium(III) tetrakis(N-methyl-4-pyridyl) porphyrin (CrTMPyP). This chapter demonstrates that the key force for the successful encapsulation of CrP inside the supercages of NaY is the electrostatic interaction between the positively-charged substituents attached on the porphyrin's macrocycle and the inherently negatively-charged building blocks of zeolite. The zeolitic framework was demonstrated by XRD and SEM. The encapsulation of CrTMPyP in NaY was demonstrated by various techniques including DGA, DRS, BET, RR. The synthesized host-guest composite (CrTMPyP@NaY) displays excellent activity in the oxidation of hydrocarbon and the hydrolysis of acetonitrile. The catalytic intermediates were investigated by using in situ DRS and RR spectroscopies. Chapter 3 shows that iron(III) tetrakis(N-methyl-4-pyridyl) porphyrin (FeTMPyP) can be entrapped into the cages of either NaY or sodalite zeolite (SOD) by controlling the initial concentration of FeP in the alurninosilicate gel, indicating the template effect of the guest molecules in crystallization process. The catalytic activity of nanoconfined FeTMPyP depends sensitively on the host structures. The FeTMPyP@SOD catalyst displays a conversion of 7.3% with over 90% selectivity for alcohol and ketone in the oxidation of cyclohexane, making our catalyst a very competitive option for the application in industrial and benchtop synthesis. Chapter 4 discusses the synthesis of vanadyl porphyrin (VOTMPyP) inside the cages of NaY and SOD zeolites by using our developed "build-bottle-around-ship" approach. The catalytic properties of VOP@NaY composite was examined by using the oxidation reaction of hydrocarbon as the probe. For the purpose of comparison, faujasite-Y confined vanadyl bis(2,2'-bipyridyl) complexes was synthesized by using the "assemble-ship-inside-bottle" method, and its catalytic activity was also studied. Chapter 5 presents the syntheses of faujasite-Y confined iron(III) and Mn(III) tetrakis- (N,N,N-trimethyl-alinilium) porphyrins (MTMAnP@NaY). The synthesized MnTMAnP@NaY composite exhibits very high activity and epoxidation selectivity in the oxidation of various alkenes. Chapter 6 summarizes the syntheses of copper and nickel porphyrin inside the supercages of faujasite-Y (MTMPyP@NaY). The hydrogenation of cyclooctadiene catalyzed by our synthesized NiTMPyP@NaY composite was fully examined. This host-guest composite can selectively catalyze the hydrogenation of cyclooctadiene to cyclooctene. The shape-selectivity was also observed in the competitive hydrogenation of cyclooctene and cyclododecene. Chapter 7 mainly displays the application of Raman spectroscopy in identifying the manganese phenanthroline complexes synthesized at different conditions by using the "assemble-ship-inside-bottle" approach. The catalytic properties of synthesized complexes were examined with the oxidation of cyclohexene as the probe.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 1998
Language English
Format Thesis
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