(560jf) Dynamic Catalysis and Surface Resonance for Turnover Frequency Enhancement

Ardagh, M. A. - Presenter, University of Minnesota
Abdelrahman, O., University of Massachusetts Amherst
Zhang, Q., University of Minnesota
Dauenhauer, P., University of Minnesota
Heterogeneous catalysts and their associated chemical reactors are key components of many chemical processes for petroleum production, fine chemical synthesis, and consumer products manufacturing. For each process, intensive reaction engineering has been employed to scale up, maximize product yields, and minimize production costs. Typical process and product development include varying temperature, pressure, catalyst selection, reactor type, and time/spacetime. For a given set of these variables, a wide range of reaction and catalyst classes have been found to obey a “volcano plot” relationship between reaction rate and several catalyst binding energy descriptors. This means that reaction engineering has a (currently) insurmountable catalytic speed limit, due to the trade-off between surface reaction rates and product desorption for a catalyst with static binding properties. In this work, we present several alternative handles for enhancing catalyst performance and chemical production rates. In this approach, catalyst binding properties are varied with time [1].

Using a CSTR model in Matlab, a model system with A → B and three elementary steps: (i) adsorption of A, (ii) surface reaction of A* → B*, and (iii) desorption of B was studied. The catalyst binding properties were varied using a square, sinusoidal, triangle, or saw-tooth waveform with a specified oscillation frequency (fosc , [=] Hz) and amplitude (ΔU, [=] eV). The dynamic steady state rate was found to be a strong function of frequency and amplitude. For moderate amplitudes between 0.5-1.5 eV, there is a resonance frequency range between 103 -107 Hz where steady state rates level off at 100-10,000x the Sabatier maximum. With practicality in mind, the oscillation waveform was tested at the same frequency and amplitude to assess their effectiveness in rate enhancement. Square waveform were the highest performing but sinusoidal waveform still led to high rate enhancement. These new process handles of frequency, amplitude, and waveform allow for reaction engineering to greatly improve process performance.

[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