Visualizing catalyst heterogeneity by a  multifrequential oscillating reaction

Abstract

It is well documented that different surface structures of catalytically active metals may exhibit different catalytic properties. This is typically examined by comparing the catalytic activities and/or selectivities of various well-defined smooth and stepped/kinked single crystal surfaces. Here we report the direct observation of the heterogeneity of active polycrystalline surfaces under reaction conditions, which is manifested by multifrequential oscillations during hydrogen oxidation over rhodium, imaged in situ by photoemission electron microscopy. Each specific surface structure, i.e. the crystallographically different µm-sized domains of rhodium, exhibits an individual spiral pattern and oscillation frequency, despite the global diffusional coupling of the surface reaction. This reaction behavior is attributed to the ability of stepped surfaces of high-Miller-index domains to facilitate the formation of subsurface oxygen, serving as feedback mechanism of the observed oscillations. The current experimental findings, backed by microkinetic modeling, may open an alternative approach towards addressing the structure-sensitivity of heterogeneous surfaces.

Effect of the Pt Precursor and Loading on the Structural Parameters and Catalytic Properties of Pt/Al2O3

“…Previous studies have reported the participation of perimeter or corner sites in CO oxidation and the WGSR . A novel explanation concerning the role of interfacial sites was that the surfaces of defects (steps and kinks) facilitated the formation of superficial oxygen, which sustained oscillations in the hydrogen oxidation activity at a polycrystalline Rh surface composed of crystals in microdomains of 10–50 μm with different orientations. Hence, in the case of the x PtAl samples, oxygen would be coordinated with the low coordination sites, which would be responsible for the CO activation.…”

Operando Insights into CO Oxidation on Cobalt Oxide Catalysts by NAP-XPS, FTIR, and XRD

“…Nevertheless, to assess the relative contributions of all pathways and to determine the rate limiting step, further studies would be required (e.g., by transient/concentration modulation IR spectroscopy 43 and detailed (micro)kinetic modeling). 23 − 25 …”

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X‐ray Probes

“…[26,27] These modifications can improve or inhibit the catalytic activity.I nc ontrast, poisoning hinders further reaction and reduces the number of available active sites. [26,27] These modifications can improve or inhibit the catalytic activity.I nc ontrast, poisoning hinders further reaction and reduces the number of available active sites.…”