Investigations of Cobalt Acetate and Titanium Nitride for Catalytic and Sustainable Chemistry

Abstract

The development of cheap industrial scale H2 production from renewable sources is highly desirable to meet our future clean-energy demands. One promising route is water splitting using solar radiation. In this thesis, the individual components of a photocatalytic system were explored with the aim of applying earth-abundant and industrially relevant catalyst materials for sustainable chemistry. A family of cobalt acetate compounds was examined as potential water and biomass oxidation catalysts, and TiN nanoparticles were investigated as co-catalysts for photocatalytic hydrogen evolution. A significant challenge for realising industrial scale water splitting is the development of efficient, stable, and earth-abundant catalysts for the water oxidation half reaction. Co(III) species have long been known to facilitate water oxidation and cobalt acetate has been employed as a versatile industrial oxidation catalyst of alkyl aromatic molecules over the last 60 years. This has inspired a series of investigations to evaluate several oligomers from a family of cobalt acetate compounds as water oxidation catalysts (WOCs). Three model Co(III) acetate oligomers of different nuclearity, the Co-cubane, [Co4(μ3-O)4(μ-OAc)4(py)4], Co-trimer, [Co3(μ3-O)(μ-OAc)6(py)3][PF6], and Co-dimer, [Co2(μ-OH)2(μ-OAc)(OAc)2(py)4][PF6] were assessed. Complementary to developing more efficient WOCs, an alternative approach is to employ sacrificial agents, such as aromatic molecules, that are more easily oxidised than water. The ability of cobalt acetate to oxidise a variety of lignin model compounds was also explored. Lastly, commercialised semiconductors (i.e. TiO2) are restricted to absorbing ~ 5% of the energy of the terrestrial solar spectrum. TiN nanoparticles were explored as co-catalysts with TiO2 (P25) for photocatalytic H2 evolution via MeOH reformation due to their unique optical properties.