2024 AIChE Annual Meeting

(669a) Leveraging the Commonalities between Thermo- and Electro-Catalysis for Understanding Aerobic Glucose Oxidation in Aqueous Media

Authors

Chung, M. - Presenter, Massachusetts Institute of Technology
Flaherty, D., University of Illinois At Urbana-Champaign
Thermocatalysts at solid-liquid interfaces resemble short-circuited electrochemical cells, where a series of concurrent oxidation and reduction half-reactions occur on conductive catalyst surfaces. Mass and charge balances require that the total current integrated across the catalyst surface equals zero, and the open circuit electrochemical potential of the catalyst describes the point where rates of coupled Faradaic reactions satisfy this requirement. Previous studies validated this electrochemical model of thermocatalysts with oxidations of hydrogen, primary alcohols, and carboxylic acids. We translate this principle to describe complex liquid-phase aerobic oxidation reactions relevant for chemical manufacturing at industrial scales.

Glucose oxidation over carbon-supported Pt nanoparticles produces precursors to platform molecules that include dicarboxylic acids (i.e., glucaric acid). High yields of glucaric acid remain challenging to achieve but the reasons evade description as does the mechanism of glucaric acid formation. To elucidate the mechanistic details, we measured steady-state rates, selectivities, and open-circuit potentials within a trickle-bed reactor as functions of oxygen pressure and inlet concentrations of glucose, gluconic, and glucaric acids. Rate measurements indicate that α-H abstraction by surface hydroxide (OH*) limits rates, and the reactions proceed on surfaces that bind high fractional coverages of glucose-derived species. Here, the operando open circuit potentiometry provided additional insight to discriminate between plausible thermocatalytic reaction mechanisms by revealing the ratio between the coverages of unreacted glucose and its oxygenated derivatives. Gluconic acid, in particular, inhibits the formation of glucaric acid by obstructing O2 activation. Isothermal titration calorimetry corroborates these interpretations and shows gluconic acid binds much more exothermically than all other reactants, intermediates, and products in glucose oxidation. This study integrates the principles of thermo- and electro-catalysis to unlock new mechanistic insights that guide strategies for maximizing profits in glucose valorization through aerobic oxidation.