Hannes Frey (Zurich / CH), Arik Beck (Zurich / CH; Villigen / CH), Armin Kleibert (Villigen / CH), Jeroen Anton van Bokhoven (Zurich / CH; Villigen / CH), Marc Georg Willinger (Zurich / CH; Garching / DE)
Abstract text (incl. figure legends and references)
In catalysis, electron microscopy is often employed to reveal atomistic information regarding the structure and composition of the fresh catalyst or to study, post-mortem or in-situ, reaction induced changes. Information is then oftentimes linked to data acquired with integral methods such as mass spectrometry or X-ray based spectroscopy methods. However, both methods fail to resolve processes that are dominant at intermediate length scales. They involve the collective transport of heat or mass and play a role in the formation and propagation of reaction fronts [1], for example. X-ray Photoelectron emission microscopy (XPEEM) enables wild field spectral imaging of planar surfaces in the micrometer range and is therefore suited to fill the information gap between local, atomic-level observation and averaging integral methods.
Hydrogen spillover concerns the surface migration of activated hydrogen atoms from a metal catalyst particle, on which molecular hydrogen dissociates, onto the catalyst support. It is of high importance for heterogeneous catalysis, hydrogen storage materials, and fuel cell technology. Its occurrence on metal oxide surfaces is established [2], yet questions remain about how far from the metal center spillover is reaching.
By employing in-situ XPEEM on a planar model catalyst [3], we were able to gather direct evidence that spillover is occurring over several microns across the oxide surface [4]. The wide filed nature of XPEEM and the tunability of the incoming X-ray beam allows for quantification of the chemical states of the oxide surface in a time resolved manner with spatial resolution. These findings and the derived understanding at which temperatures hydrogen spillover in affecting the surface will help to improve and exploit the process of hydrogen spillover for application.
Figure 1. Time and spatial resolved oxidation state of oxide film during exposure to hydrogen. Color resembles oxidation state: Red = fully oxidized, blue = reduced. Reduction is initiated at metal (indicated by lines) and propagates over the oxide support.
1] C. Barroo, Z.-J. Wang, R. Schlögl, M.-G. Willinger, R. Schlögl. Nat. Catal., 2019, 3, 30–39.
[2] Prins R. Chem. Rev., 2012, 112(5), 2714-2738
[3] Karim W., Spreafico C., Kleibert A., Gobrecht J., Vandevondele J, Ekinci Y., van Bokhoven J. A. Nature, 2017, 541(7635), 68-71.
[4] Beck A., Frey H., Willinger M-G., Kleibert A., van Bokhoven J. A. in preparation