Speaker
Description
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 interfaces [1]. Three examples of model and technological catalysts illustrate what can be learnt from synchrotron based spectroscopic and microscopic studies.
i) Operando APXPS/SFG/MS:
CO oxidation on Pt/ZrO2 prepared by atomic layer deposition (ALD) was examined by sum frequency generation (SFG) spectroscopy and ambient pressure X-ray photoelectron spectroscopy (AP-XPS @MAX IV), combined with mass spectrometry (MS) [2]. Complemented by Density Functional Theory (DFT), we show that the reaction onset is determined by a delicate balance between CO disproportionation and oxidation.
ii) In situ SPEM/PEEM:
H2 oxidation on polycrystalline Rh was studied by scanning photoelectron microscopy (SPEM @ELETTRA) and photoemission electron microscopy (PEEM), which allow local surface analysis and visualising the heterogeneity of ongoing reactions on a µm-scale [3]. This revealed an anisotropy of surface oxidation, yielding an oxidation map. In situ PEEM imaging of ongoing H2 oxidation directly compares the local reactivity of metallic and oxidised Rh, revealing a high transient activity of Rh surface oxide, providing a direct imaging of a structure-activity relation for plenty surface structures. In a follow-up SPEM study [4], an unknown coexistence of four different states was observed: an active steady state, an inactive steady state and multifrequential oscillating states.
iii) Operando APXPS/XANES/MS:
Turning from model systems to applied catalysis, AP-XPS and X-ray absorption near edge structure (XANES @SLS/PSI) were employed to characterize Ni/ZrO2 and Ni/MgO-ZrO2 upon H2 pretreatment and during Partial Oxidation of Methane (POM) to Syngas at 750 ⁰C (activity monitored by inline MS). During POM (partial) Ni re-oxidation occurred, although Niº is often suggested as active phase, but the Ni oxidation state was sensitive to feed gas changes.
The insights by monitoring ongoing reactions may stimulate new ways of catalyst design.
References
1. G. Rupprechter, Small (2021) 2004289
2. V. Pramhaas et al., ACS Catalysis 11 (2021) 208–214
3. P. Winkler et al., Nature Communications 12 (2021) 69
4. P. Winkler et al., Nature Communications 12 (2021) 6517
5. J. Asencios et al., in preparation
Acknowledgements: Work supported by the Austrian Science Fund (FWF) and the Austrian Academy of Sciences (ÖAW).
| I apply for a travel grant | No |
|---|
