Concepts and tools for integrating multiscale dynamics into reaction kinetics

Abstract

Concepts are introduced for quantitatively incorporating multiscale dynamic processes into reaction kinetics during heterogeneous catalysis. Across the active sites, catalyst surface, grain, pellet, and reactor bed, these concepts allow for the coupling of reaction, diffusion, and dynamics. Open catalytic cycles that lead eventually to closed catalytic cycles while incorporating active site ensemble evolution and transformation are proposed. Modified, periodic, aperiodic (chaotic) and complex catalyst surfaces are examined and quantitatively incorporated into conventional kinetic models that utilize the mass-action law. Quantifying dynamics requires examination of the changes of adsorption and desorption with coverage of species over modified, periodic, aperiodic and complex surfaces. Population balance models allow the integration of particle size, and shape dynamics into reaction kinetics. The oscillation theory predicts dynamics in catalyst pellets where bubbles are nucleated, transported, and compete with liquid heat and mass transport. Modulation of the feed using sinusoids, step responses, pulses, and ramps provide dynamics at the reactor bed scale. To bring these concepts together, a particle-resolved transient kinetic model quantifies and incorporates dynamics at various scales (grain, pellet, and reactor bed) into reaction kinetics. Integration with first principles-based kinetic Monte Carlo simulations (pore scale integration) and computational fluid dynamics (reactor scale integration) brings a holistic quantitative view of the influence of chemical and particle dynamics on reactor performance. System dynamics incorporated in stochastic-deterministic models allow for simulations of state-transitions during flow. Exampes are drawn from metal catalysis and zeolite catalysis and a case-study is provided for methanol-to-olefin conversion over zeolite catalysts.