(247a) From Non-Steady State Vehicle Emissions Control to Distributed Chemicals Production Using Forced Dynamic Operation of Small-Scale Reactors

Catalytic cycles on heterogeneous catalysts involve the adsorption of reactants, followed by one or more activated surface reaction steps before products desorb. In general, catalysts with high binding affinity can greatly accelerate adsorption and activation of reactants, but surface intermediates or products may become overly abundant and poison the surface. This trade-off is commonly conceptualized as the Sabatier volcano, which imposes an upper limit to the steady-state activity of a catalyst. Inspired by Harold’s seminal contributions to vehicle emission control catalysis under non-steady state conditions, we have identified small-scale reactors, operated using forced dynamic oscillation, as promising strategy to dynamically enhance catalytic activity.

In experimental studies by Harold and others, it has been reported that the yield of (selective) oxidation reactions on multicomponent catalysts with dynamic oxygen storage capacity can often be improved through lean/rich cycling by changing the feed composition. Examples include methane partial oxidation over Pt-group metals (PGMs) on oxide supports, propylene ammoxidation over promoted bismuth molybdate, and even CO oxidation. In this talk, I will discuss fundamental aspects of dynamic rate improvements as derived from detailed kinetic and reactor models. In all examples, surface coverage effects play a dominant role, including the build-up of inhibiting intermediates and the relative abundance of different oxygen species. Our studies suggest that through modulation of feed conditions the surface environment can be transiently controlled to provide optimal conditions for the desired reaction events. Overall, forced dynamic operation of modular reactors are an exciting opportunity to advance the processes needed to realize a sustainable energy transition.