(205f) Dynamic Modulation of Catalyst Electronic Structure to Enhance Reaction Rates

Ardagh, M. A. - Presenter, University of Minnesota
Wang, Y., University of Minnesota
Abdelrahman, O., University of Massachusetts Amherst
Zhang, Q., University of Minnesota
Frisbie, C. D., University of Minnesota
Dauenhauer, P., University of Minnesota
Heterogeneous catalysts are prevalent in chemical industry processes for the manufacture of consumer goods, petroleum conversion to gasoline, and pharmaceutical synthesis. Even for well defined, mature processes there is ongoing research to minimize production costs and improve catalyst performance. The electronic structure of the catalyst has a significant effect on reaction activity and selectivity, because electronic structure affects catalyst binding properties and reaction activation energies. Since many reaction and catalyst classes have been shown to follow a volcano plot relationship between reaction rate and various catalyst binding energy descriptors, there is a trade-off between speeding up the surface reaction kinetics and product desorption. Therefore, catalyst selection and electronic structure optimization can at most improve catalyst performance up to this speed limit.

In this talk, we present an alternative approach where catalyst electronic structure, and therefore binding properties, are varied as a function of time [1]. The effectiveness of this approach was demonstrated using a CSTR with a model A → B system that has three elementary steps: (i) adsorption of A, (ii) surface reaction of A* → B*, and (iii) desorption of B. Binding properties were varied with a square, sinusoidal, triangle, or saw-tooth waveform with a specified oscillation frequency (fosc , [=]Hz) and amplitude (ΔU, [=] eV). Experimentally, this electronic structure oscillation can be implemented with back-gate voltage, applied strain, and varying feed pressure/composition. Computationally, we found that steady state rates depend strongly on the frequency and amplitude. For moderate oscillation amplitudes (0.5-1.5 eV), the steady state rate has a resonance frequency range between 103 -107 Hz where the rate plateaus at up to 10,000x greater than the Sabatier maximum. With practical implementation in mind, various oscillation waveform were compared to assess their effectiveness. Square waveform had the highest performance but the sinusoidal waveform also led to high rate enhancement.

[1] M. A. Ardagh, O. A. Abdelrahman, P. J. Dauenhauer, “Principles of Dynamic Heterogeneous Catalysis: Surface Resonance and Turnover Frequency Response” ChemRxiv Preprint, 2019. doi.org/10.26434/chemrxiv.7790009.v1