Shadowing Effect in Catalyst Activity: Experimental Observation

Abstract

The influence of the spatial distribution of catalyst particles in a fixed bed reactor on the observed reaction rates has historically been of central interest in catalysis and chemical physics. Results from both fields suggest that the apparent catalyst activity is determined by the distance between active particles and transport phenomena, although a universal understanding of their combined influence remains incomplete. In this study, pulse experiments under contrasting transport regimes show that a given amount of catalyst particles exhibits higher activity with increasing degrees of separation. This is attributed to a shadowing effect induced by the competition between closely neighboring active particles, which limits their combined apparent activity. Experimental results also suggest the dependence of this effect on mass transport phenomena within the reactor space.

Interparticle Distance Matters for Selectivity Control in Industrially Relevant CO Electrolysis

“…Here we employed numerical calculations to estimate the local CO concentration and local pH near Cu nanoparticles at different average interparticle distances. ,, The local CO concentration ( c [CO] ) profile near one Cu nanoparticle during CO electrolysis was simulated by COMSOL simulations using a two-dimensional (2D) model (Figure S14) and the CO consumption rate based on the electrolysis performance at an applied geometric current density of 400 mA cm –2 (Figure S15). The decrease in the local CO concentration (namely, relative Δ c [CO] ) near one Cu nanoparticle caused by CO electrolysis over all available neighboring Cu nanoparticles was calculated by further considering the volumetric density of Cu nanoparticles in catalysts layers. As shown in Figure c,d, the decrease in the local CO concentration is more obvious at smaller interparticle distances.…”

“…In other words, the local CO concentration increases with increasing interparticle distance. The negative effect of the competitive consumption of reactant (i.e., CO) over adjacent nanoparticles gradually becomes weaker at larger interparticle distances. ,,,, On the other hand, local pH on the surface of one Cu nanoparticle during CO electrolysis was also estimated using the consumption rate of H + (thus, the formation rate of OH – ). As the formation of OH – was proportional to the applied current density regardless of the products, the OH – formation rate was calculated by the applied total current and the total Cu surface area for each electrode at an applied geometric current density of 400 mA cm –2 .…”