When atomic-scale resolution is not enough: Spatial effects in in situ model catalyst studies

TL;DR

This study uses multi-scale modeling to reveal how spatial flow effects influence catalyst activity measurements, showing that flow setup significantly impacts the interpretation of surface reactions.

Contribution

It introduces a multi-scale modeling approach combining kinetic Monte Carlo and fluid dynamics to analyze spatial effects in in situ catalyst studies.

Findings

Flow setup affects pressure and surface composition variations.

Lateral changes hinder direct structure-activity correlations in channel flow.

Stagnation flow allows clearer structure-activity analysis.

Abstract

We investigate transport effects in in situ studies of defined model catalysts using a multi-scale modeling approach integrating first-principles kinetic Monte Carlo simulations into a fluid dynamical treatment. We specifically address two isothermal flow setups: i) a channel flow with the gas-stream approaching the single crystal from the side, as is representative for reactor scanning tunneling microscopy experiments; and ii) a stagnation flow with perpendicular impingement. Using the CO oxidation at RuO2 (110) as showcase we obtain substantial variations in the gas-phase pressures between the inlet and the catalyst surface. In the channel geometry the mass transfer limitations lead furthermore to pronounced lateral changes in surface composition across the catalyst surface. This prevents the aspired direct relation between activity and catalyst structure. For the stagnation flow the lateral variations are restricted to the edges of the catalyst. This allows to access the desired structure-activity relation using a simple model.