Date of Award

5-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Craig Barnes

Committee Members

Sheng Dai, Mark Dadmun, Joseph Bozell

Abstract

The primary focus of this work was to synthesize and characterize boron-containing cobalt catalysts for selective catalytic transfer hydrogenation (CTH) of several reducible substrates in the interest of lignin valorization applications. Lignin is of interest because it is the most abundant natural source of aromatic nuclei, and a potential competitor with non-renewable petroleum as a source of fuels and value-added chemicals. CTH reactions are a potential route towards effectively reducing lignin’s oxygen content. Most CTH catalysts involve expensive noble metals, thus there is interest in discovering earth-abundant catalysts based on Fe, Co, and Ni. Two types of heterogeneous B-containing Co catalysts (“CoB”) that exhibit high activity and selectivity for catalytic transfer hydrogenation of carbonyl groups.CoB catalysts were synthesized using a facile aqueous reduction protocol under air-free conditions and are highly responsive to a strong magnet. The as-synthesized batch was exposed to air (“oxidized” CoB (CoBoxi), and the rest was stored in an inert atmosphere glovebox (“reduced” CoB (CoBred)). They were characterized using inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (PXRD) and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX). Product distributions and catalyst parameters were quantified by gas chromatography-mass spectrometry (GC-MS). PXRD indicated that both catalysts are amorphous and ICP-OES showed the atomic ratios of CoBoxi are Co1.7BO1.7 and CoBred are Co1.7B. TEM revealed that both consist of amorphous particles of various sizes encased in a 2-3 nm layer of an amorphous coating. EDX showed that cobalt and boron are uniformly distributed throughout the particles. Post-reaction characterization with STEM revealed the formation of crystalline Co and Co3O4 phases on the catalyst surfaces.CoBred was shown to be the most active catalyst under all conditions tested. The activity of CoBoxi was significantly lower, suggesting that the active site may be a reduced species. A pretreatment protocol was used to enhance the activity of both catalysts. All CoB catalysts were shown to be active at 100 °C, and their selectivities can be tuned in certain cases by modifying the reaction parameters. The results described in this work reveal that B-containing Co materials are selective catalysts for CTH.

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