In a heterogeneously catalyzed reaction surface diffusion determines the mixing of reactants and their lateral transport on the surface. This process is usually regarded to happen on a short time scale compared to the reaction, so that it can be neglected in the rate equations. However, at the high pressures applied in industrial processes the surface of a catalyst can be highly covered by adsorbed particles, and one may expect reduced mobility by site blocking. Whether adsorbed particles are still sufficiently mobile on such a "crowded" surface is unclear as well as the atomic mechanism of such a diffusion process. We have investigated the diffusion of single oxygen atoms on a fully CO covered Ru(0001) surface. The experiments were performed using a video-rate, variable temperature scanning tunneling microscope (STM). STM videos were recorded over extended periods of times and over a wide range of temperatures. The data were analyzed by means of a particle tracking algorithm that could monitor atomic trajectories over thousands of consecutive STM images. A mathematical model consisting of two different hopping processes reproduced the experimental displacement distributions. Complementary calculations by density functional theory (DFT) provided a step-by-step picture of the atomic mechanism. The diffusion of the O atom through the CO layer can be described as a "door-opening" mechanism in which local density fluctuations in the CO layer create low-energy diffusion pathways for the O atom. The resulting mobility is surprisingly high, pointing to a general explanation for high diffusion rates on catalyst surfaces.

Atomic-scale observation of diffusion on a crowded catalyst surface

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.