Combining high-energy X-ray diffraction with Surface Optical Reflectance and Planar Laser Induced Fluorescence for operando catalyst surface characterization

Abstract

We have combined three techniques, High Energy Surface X-Ray Diffraction (HESXRD), Surface Optical Reflectance, and Planar Laser Induced Fluorescence in an operando study of CO oxidation over a Pd(100) catalyst. We show that these techniques provide useful new insights such as the ability to verify that the finite region being probed by techniques such as HESXRD is representative of the sample surface as a whole. The combination is also suitable to determine when changes in gas composition or surface structure and/or morphology occur and to subsequently correlate them with high temporal resolution. In the study, we confirm previous results which show that the Pd(100) surface reaches high activity before an oxide can be detected. Furthermore, we show that the single crystal catalyst surface does not behave homogeneously, which we attribute to the surface being exposed to inhomogeneous gas conditions in mass transfer limited scenarios.

Operando Reflectance Microscopy on Polycrystalline Surfaces in Thermal Catalysis, Electrocatalysis, and Corrosion

“…It should also be noted that there is an initial “jump” in reflectivity loss as the grains transition into the active regime, as shown in the magnified region of panel (b). This is consistent with previous studies 17 , 18 and may be due to a thinner layer of oxide forming as the gas composition changes when the reactant gases are depleted by the chemical reaction. Other details of note are the spatial gradients visible on the edges of some of the grains in panel (e), for example, the one at the tip of the red arrow.…”

“…This would build on previous studies where PLIF has been combined with 2D-SOR on single crystals. 16 , 17 It would then be possible to directly correlate a local change in the reflectivity with a local change in catalytic activity.…”

High energy surface x-ray diffraction applied to model catalyst surfaces at work

“…Since it has moreover been found that even the catalyst surface of a single crystal model catalyst may not always behave homogeneously, e.g. due to inhomogeneous gas distributions around the sample [144], a technique that visualizes the surface morphology/optical properties of the whole sample surface at the same time is essential.…”

“…Instrum. 90 033703 (2019) [133], with the permission of AIP Publishing. sapphire reactor dome [133].…”

Copper catalysis at operando conditions—bridging the gap between single nanoparticle probing and catalyst-bed-averaging

“…Consequently, this combination of integral activity measurements with single point probing of catalyst material state is prone to produce erroneous structure-function relationships 9,10 . In attempts to alleviate this problem, recent studies have used a combination of techniques to both spatially and temporally investigate model 3,[11][12][13][14][15][16][17] and more complex catalysts 9,11,12,[18][19][20][21][22] , with several comprehensive reviews on the topic published recently 2,9,10,23 . For example, the thin 150 μm capillary used in Spaci-MS 2 enables spatiotemporal characterization of reactant gradients with a spatial resolution of ca.…”