Catalytic Resonance Theory: Kinetics and Frequency Response of Light-Promoted Catalysis

Abstract: The illumination of catalytic surfaces with a continuous or pulsed stream of photons dynamically modulates surface chemistry for faster rates, higher conversion, or product selectivity control. To establish fundamental principles of dynamic photon-modulated catalysis, the photocatalytic conversion of a generic surface reaction was simulated to understand the kinetic implications of an independent stream of photons promoting surface product desorption. Simulations were conducted via the microkinetic model and kinetic Monte Carlo methods for the scenarios of a Poisson distribution, constant spacing between photons, and coordinated on/off pulsing of photon sources. The time-averaged photocatalytic rate at differential conditions for varying photon flux and temperatures indicated three kinetic regimes described by product thermal desorption control, surface reaction control, and an intermediate kinetic regime with a zero slope Arrhenius plot, consistent with a degree of rate control dominated by the photon arrival frequency (i.e., per-site photon flux). The maximum photocatalytic rate occurred orders of magnitude above the Sabatier limit at the resonance frequency, identified as the photon arrival frequency that matched the surface reaction rate constant. Non-equilibrium photocatalytic conversion occurred when the rate of photon-promoted product desorption was comparable to the rate of thermal product desorption. Results indicated the general utility of photon-promoted catalysis, with negligible benefit for rate enhancement and quantum yield with photon source pulsing or chopping due to the inherent dynamic nature of photons from light sources.