Operando and Theoretical Surface Science Studies of Heterogeneous Catalysts. Symposium in connection to David Langhammer’s thesis

Symposium in connection to David Langhammer’s thesis 26 March.

Chair: Prof. Lars Österlund, Div. Solid State Physics, Dept. Materials Science and Engineering

10.15 – 11.00 Prof. Günther Rupprechter, Institute of Materials Chemistry, TU Wien, Austria: "Operando Surface Spectroscopy and Microscopy During Catalytic Reactions"

Abstract: Operando characterization of working catalysts, requiring the simultaneous measurement of catalytic performance, is crucial to identify the relevant catalyst structure/composition and how molecules interact with surfaces/interfaces. Two examples, covering nanoparticles, thin films and meso-scale aggregates, bridge the "materials and pressure gaps".

i) Area-averaging operando spectroscopy: CO oxidation on Pt/ZrO2 prepared by atomic layer deposition (ALD) was examined by sum frequency generation (SFG) spectroscopy and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), combined with mass spectrometry (MS) [1]. Combining experimental data with ab initio Density Functional Theory (DFT), we show that the reaction onset is determined by a delicate balance between CO disproportionation (Boudouard reaction) and oxidation. Disproportionation occurs on low-coordinated Pt sites at high CO coverages, when the remaining C-atom is stabilized by a favorable coordination. At variance with the general expectation, rough Pt nanoparticles are seemingly less active than smoother Pt films.

ii) Spatially-resolved operando microscopy: H2 oxidation on polycrystalline Rh was studied by scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM), which allow local surface analysis and visualising the heterogeneity of ongoing reactions on a µm-scale [2]. This revealed an anisotropy of surface oxidation (depending on the local step/edge density, yielding an oxidation map), as well as its effect on catalytic activity. In situ PEEM imaging of ongoing H2 oxidation directly compares the local reactivity of metallic and oxidised Rh, demonstrating the effect of surface oxides. Employing the velocity of propagating reaction fronts as indicator of reactivity, a high transient activity of Rh surface oxide was observed. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty well-defined surface structures within one sample.

[1] V. Pramhaas et. al, ACS Catalysis, 11 (2021) 208–214
[2] P. Winkler et al, Nature Communications, 12 (2021) 69

11.00 – 11.30 Prof. Per-Anders Carlsson, Dept. Chemistry and Chemical Engineering, Chalmers University of Technology, Göteborg: "In Situ Time-Resolved FTIR Spectroscopy in Heterogeneous Catalysis"

11:30 – 12:00 Dr. Jolla Kullgren, Dept. Chemistry - Ångström, Uppsala University: "Characterization of Defects at The Ceria Surface Using Simulations"

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Last modified: 2021-02-14