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Synthesis and characterization of titanium-containing molecular sieves

Citation

Dartt, Christopher Bruce (1996) Synthesis and characterization of titanium-containing molecular sieves. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-12122007-111327

Abstract

The use of zeolites and molecular sieves as catalysts for important organic reactions is reviewed. One emerging area of particular interest is the use of titanium-containing molecular sieves as partial oxidation catalysts and is chosen for further study.

In order to elucidate the relationships between the physicochemical properties of titanium-containing molecular sieves and their ability to act as partial oxidation catalysts, titanium-containing pure-silica ZSM-5 (TS-1) materials are synthesized using different methods. The activities of the titanium-containing catalysts for the oxidation of alkanes, alkenes, and phenol at temperatures below 100 [degrees]C using aqueous hydrogen peroxide H2O2 as the oxidant are reported. The relationships between the physicochemical and catalytic properties of these titanium silicates are discussed. The effects of added aluminum and sodium on the catalytic activity of TS-1 are described. The addition of sodium during the synthesis of TS-1 is detrimental to the catalytic activity while sodium incorporation into pre-formed TS-1 is not. The framework substitution of aluminum for silicon appears to decrease the amount of framework titanium.

The relationships between catalytic performance and physicochemical properties that are controlled through synthetic methods are further investigated using a series of titanium-containing molecular sieves. Titanium-containing pure-silica ZSM-5 (TS- 1), pure-silica ZSM-48 (Ti-ZSM-48) and zeolite beta (Ti-Al-beta) are synthesized and characterized by X-ray powder diffraction (XRD), elemental analysis, physical adsorption of N2, Fourier transform infrared (FT-IR), FT-Raman, and diffuse reflectance ultraviolet (DR-UV) spectroscopies. TS-1 is synthesized by five different methods. All materials are evaluated for their ability to oxidize 1-hexene and n-octane using aqueous H2O2 as the oxidant. The relationships between the physicochemical and catalytic properties of these titanium-containing zeolites are discussed. TS-1 samples synthesized at high pH are catalytically active and framework titanium is shown to be necessary for olefin epoxidation and alkane hydroxylation to occur. The existence of anatase in active TS-1 samples results in decreased hydrogen peroxide efficiencies in the epoxidation reaction. TS-1 produced at pH=7.4 and Ti-ZSM-48 each contain anatase and are not active. Ti-beta is found to contain framework titanium and be free of anatase. However, at the conditions used in this study these samples are not able to activate 1-hexene or n-octane.

In attempts to prepare large pore titanium-containing molecular sieves, postsynthetic incorporation of titanium in the borosilicate SSZ-33 and the direct synthesis of an aluminum-free titanium-containing zeolite Beta (Ti-Beta) are reported. These materials are characterized by XRD, FT-IR, FT-Raman, and DR-UV spectroscopies. The molecular sieves are shown to catalyze the epoxidation of various olefins using aqueous hydrogen peroxide as the oxidant. The physicochemical properties as found by the characterization methods are correlated to the catalytic data and the results compared to a high quality sample of TS-1. The modified SSZ-33 samples contain titanium primarily in the form of isolated tetrahedrally coordinated Ti atoms, although some extra-framework Ti is observed by Raman and DR-UV spectroscopies. Ti-Beta samples show no evidence of extra-framework titanium. For the epoxidation of cis-cyclooctene, the Ti-Beta catalysts give quantitative conversion to epoxide, and both the Ti-Beta and Ti-SSZ-33 catalysts are able to epoxidize substrates too large to be oxidized by TS-1.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Davis, Mark E.
Thesis Committee:
  • Davis, Mark E. (chair)
  • Gavalas, George R.
  • Flagan, Richard C.
  • Zones, Stacey I.
Defense Date:17 May 1996
Record Number:CaltechETD:etd-12122007-111327
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-12122007-111327
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4972
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:13 Dec 2007
Last Modified:26 Dec 2012 03:13

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