Collaborative Research: Resolving the Contributions of Lattice Oxygen, Dioxygen, Acid Sites, Base Sites, and Redox Sites during the Oxidative Scission of Ketones on Metal Oxides

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

The project addresses sustainable chemical manufacturing based on catalytic upgrading of platform (i.e., intermediate) chemicals derived from renewable biomass. Specifically the research focuses on biomass-derived chemicals that contain ketone groups. Oxidation of the ketone groups produce a wide range of commodity chemicals that include aldehydes, ketones, carboxylic acids, diacids, and acid anhydrides – most of which are presently manufactured from fossil-derived resources, with large carbon footprint. However, over-oxidation – the tendency of the oxidation process to continue beyond production of high-value chemicals, and extend into the combustion realm – represents a significant challenge to widespread deployment of biomass based chemical manufacturing. The project addresses this challenge by identifying the key steps and intermediate species in ketone oxidation that contribute to over-oxidation, thereby providing chemical insights regarding catalyst designs that minimize over-oxidation and produce higher yields of high-value chemical products. Beyond the technical aspect, the project is marked by educational and outreach initiatives highlighted by activities that focus on building computer programming skills and enabling the ethical use of artificial intelligence in scientific research. The oxidative scission of ketones is usually performed over vanadium oxides dispersed onto high surface area carriers such as gamma-Al2O3. Those catalysts display outstanding activity, but they achieve only modest selectivity. Even under optimal conditions, the oxidative scission of ketones over vanadium oxides will produce roughly 30% yield to CO and CO2 through undesired combustion reactions. Combustion pathways appear to target intermediate carboxylate species, which bind strongly to catalyst surfaces, and instead of desorbing as a stable carboxylic acid product, react with oxygen sources to form carbon oxides, reducing the yield of desired products. The project is based on preliminary data suggesting that the key to enhancing selectivity during oxidative scission is to accelerate carboxylate desorption relative to carboxylate combustion. Doing so hinges on understanding of the mechanisms of combustion and oxidative scission on complex reducible solid oxide surfaces that are populated by numerous Brønsted sites, Lewis sites, and Redox sites. The project seeks to provide a quantitative, elementary description of the mechanism(s) of oxidative scission over metal oxides. This is accomplished through coupled experimental and computational research, namely steady-state and transient kinetic analysis, in situ spectroscopy, electronic structure calculations, microkinetic modeling, and uncertainty quantification. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.