Principles of Dynamic Heterogeneous Catalysis: Surface Resonance and Turnover Frequency Response
2019-03-01T16:32:14Z (GMT) by
Acceleration of catalytic transformation of molecules via heterogeneous materials occurs through design of active binding sites to optimally balance the requirements of all steps in a catalytic cycle. In accordance with the Sabatier principle, the characteristics of a single binding site are balanced between at least two transient phenomena, leading to maximum possible catalytic activity at a single, static condition (i.e., a ‘volcano curve’ peak). In this work, a dynamic heterogeneous catalyst oscillating between two electronic states was evaluated to demonstrate catalytic activity as much as three-to-four orders of magnitude (1,000-10,000x) above the Sabatier maximum. Surface substrate binding energies were varied by a given amplitude (0.1 < ΔU < 3.0 eV) over a broad range of frequencies (10<sup>-4</sup> < <i>f</i> < 10<sup>11</sup> s<sup>-1</sup>) in square, sinusoidal, sawtooth, and triangular waveforms to characterize surface dynamics impact on average catalytic turnover frequency. Catalytic systems were shown to exhibit order-of-magnitude dynamic rate enhancement at ‘surface resonance’ defined as the band of frequencies (e.g., 10<sup>3</sup>-10<sup>7</sup> s<sup>-1</sup>) where the applied surface waveform kinetics were comparable to kinetics of individual microkinetic chemical reaction steps. Key dynamic performance parameters are discussed regarding industrial catalytic chemistries and implementation in physical dynamic systems operating above kilohertz frequencies.