UC Santa Barbara

Humankind must soon contend with its dependence on nonrenewable carbon sources. Apart from their role in powering our cars and homes, fossil fuels such as petroleum and natural gas also function as the source material for over 99% of global chemical production by volume. These hydrocarbons eventually go on to comprise at least 95% of all manufactured goods, totaling over 800 million metric tons each year, with roughly half due to plastics alone. Complicating matters further, the methods for generating and disposing of such products continues to saturate the atmosphere with greenhouse gases. A more sustainable feedstock alternative for deriving the fuels and products society relies upon every day is inevitably needed. One such source material with particular promise to supplant fossil fuels is lignocellulosic biomass. Composed of cellulose, hemicellulose, and lignin, this material is available in many forms such as woody biomass or agricultural refuse, making it the planet’s most abundant form of renewable carbon. Described herein are efforts towards developing and optimizing catalytic systems for the valorization of biomass-derived oxygenates. A central goal throughout has been to better understand how these compounds’ unique properties dictate their interactions with molecular and/or solid catalysts to better guide future utilization. First, a tunable sol-gel synthesis was created to generate an array of sulfated zirconia (SZ) solid acid catalysts for the cyclodehydration of the C6 sugar alcohol, sorbitol. Characterization of acid sites and morphology were used in conjunction with kinetic studies to uncover specific parameters governing catalyst activity and product selectivity. Secondly, a bifunctional Ir-ReOx/C catalyst for sequential deoxydehydration (DODH) and catalytic transfer hydrogenation (CTH) of bio-derived mucic acid to a sustainable nylon precursor was studied. Using isopropanol as a solvent and reductant, the bimetallic catalyst exhibited remarkable activity despite its low noble metal content (0.05 wt% Ir), aiding in overall process cost reduction. Lastly, the two concluding sections involve deoxygenation of sustainable biomass polyols with molecular or ionic Re-oxo catalysts via the redox pair Re(VII)/Re(V). Through a tandem DODH/hydroboration-oxidation (DODH/HB-O) approach, renewably sourced triols and polyols were converted into their corresponding α,ω-diols with high selectivity. On the other hand, the latter instead details the regioselective installation of protecting groups on C4 and C6 sugar alcohols, as well as their subsequent DODH to unsaturated α,ω-diols. By employing alcohols as reaction solvents in these processes, the need for high pressure H2 is eliminated through their added utility as sacrificial reductants.