Year of Award

2011

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry (Inorganic Option)

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Edward Rosenberg

Commitee Members

Nigel Priestley, Bruce Bowler, Earle Adams, Nancy Hinman

Keywords

Inorganic, Material, NMR, Polymer, Silica, Surface

Abstract

The goals of this dissertation were to explore the surface characteristics of silica polyamine composites (SPC) by elucidating coordination environments, measuring surface stability, and comparisons with analogous materials. Application of SPC materials as supports for heterogeneous catalysts was also investigated. Analytical techniques including NMR (both solution state and solid state), mercury porosimetry, and scanning electron microscopy (SEM) were used to characterize the materials.

Cobalt was found to irreversibly bind to the chelating polymer polyethyleneimine (PEI). This was due to oxidation of Co2+ to Co3+, which was enabled by the chelate's ligand field stabilization. Detailed analysis of SPC surface coordination environments elucidated the types of coordination environments present. The use of model complexes further clarified the complexes forming on the composite surfaces.

Silica surfaces, including those of composite materials, are sensitive to alkaline conditions. Composite surface modifications such as the silanization step of SPC synthesis are shown to affect alkaline stability. Increasing surface group bulkiness and hydrophobicity circumstantially increased material stability. Anisotropy calculations utilizing solid-state CPMAS NMR spinning side bands were used to characterize some of the bulky, aromatic surface modifications.

A sol-gel method initially based upon the work of Dong and Brennan was developed to synthesize a composite material analogous to SPC materials. Initial materials were formed using methyltrimethoxysilane (MTMOS) and 3-chloropropyltrimethoxysilane (CPTMOS). Some control over surface morphology was achieved by adjusting synthetic conditions. Due to relatively low metal capacities, tetramethoxysilane (TMOS) was introduced as a structural support. Materials incorporating TMOS had metal capacities comparable with SPC materials, as well as narrower average pore size distributions.

Second row transition metal catalysts immobilized on SPC materials were investigated for olefin hydrogenation activity. Hydrogenation of monoenes and dienes was investigated and found comparable to currently used catalysts in some cases. The most potentially useful result of this catalysis work was the selective hydrogenation of a conjugated diene to a monoene. Selective heterogeneous hydrogenation of dienes to monoenes has potential industrial applications.

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© Copyright 2011 Jesse James Allen