Cook, Daniel Sean (2017) Solvothermal synthesis of oxides for catalysis. PhD thesis, University of Warwick.

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Abstract

Hydro(solvo)thermal synthesis was used to synthesise a range of oxide, oxyhydroxide and hydroxide materials. Their structures were characterised by a wide variety of diffraction, spectroscopic, and other analytical techniques. Many of the oxides were screened for potential applications in catalysis.

High energy X-ray diffraction was used to follow in situ the crystallisation of a cobalt gallium oxide prepared from metallic gallium in ethanolamine. Two transient metastable layered double hydroxide phases were observed prior to the formation of the spinel product when a solvent of 1:1 water:ethanolamine mixture was used. Photocatalytic studies showed that the spinel had activity as a water oxidation catalyst.

A different cobalt gallium oxide spinel was prepared by solvothermal reaction using pre-formed γ-Ga2O3 and a solution of Co2+. Its metastable structure was characterised by a variety of techniques including analysis of Bragg and diffuse neutron scattering data. The material was investigated for three-way catalysis.

The polymorphism of Ga2-xAlxO3 was investigated and the structures of materials characterised. The solvothermal synthesis of the defect spinel γ-Ga2-xAlxO3 in 2-propanol was optimised for 240 °C with up to 90% of the Ga replaced by Al. A novel oxyhydroxide Ga5-xAlxO7(OH) was prepared by solvothermal reaction in 1,4-butanediol. Solid-state MAS NMR was used to determine the coordination of the metals in these materials. All the materials are found to be metastable, transforming into thermodynamically stable polymorphs above 1400 °C. Ga2O3 and Ga2-xAlxO3 polymorphs were tested as palladium supports in the diesel oxidation reaction and the semi-hydrogenation of acetylene.

A novel oxyhydroxide, Ga2.52V2.48O7.31(OH)0.69, was prepared by reaction of Ga metal and Na3VO4 in a 1:1 ethanolamine:water mixture. The structure of this material was investigated by neutron diffraction and found to isostructural with the minerals tohdite and nolanite. The material is metastable, dehydrating around 300 °C to form Ga2.52V2.48O8, and then decomposing above 500 °C. The material was found to show good activity as a catalyst for oxidative propane dehydrogenation.
A new chromium substituted γ-Ga2O3 has been prepared and characterised. This material was prepared by solvothermal reaction in 1,4-butanediol and found to be very poorly crystalline. The spinel is stable to 900 °C before phase separating into its respective binary oxides.

The hydrothermal reaction of RhCl3·3H2O with AO2 or A(OH)2 (A = Ca, Sr, Ba) in either NaOH or KOH at 200 °C yielded a range of hydroxides. Ca3Rh2(OH)12 and Sr3Rh2(OH)12 are hydrogarnets which can be dehydrated to oxides on heating. A new hydroxide in the system Ca-Na-Rh-OH was synthesised. Reaction with barium salts in NaOH yielded BaNaRh(OH)6 a new hydroxide. The structure of this material was solved by single crystal diffraction and found to contain isolated Rh-OH octahedra, two crystallographically different 8 coordinate Na sites and a 10 coordinate Ba site.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Heterogeneous catalysis., Oxides., Metallic oxides., High temperature chemistry.
Official Date:	September 2017
Dates:	Date Event September 2017 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Walton, Richard I.
Extent:	xi, 297 leaves : illustrations, charts.
Language:	eng

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