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Laser Spectroscopy for Nanoparticle Shape Analysis reported in Angewandte Chemie International Edition

Polarization-dependent sum-frequency-generation (SFG) spectroscopy of adsorbed CO enabled to characterize the morphology of oxide-supported metal nanoparticles. The joint study with the Fritz Haber Institute (Berlin, Germany) was published in Angewandte Chemie International Edition.

Molecules on inclined facets: Polarization-dependent sum-frequency-generation (SFG) spectroscopy of adsorbed CO was employed to characterize the morphology of oxide-supported Pt and Pd nanoparticles. Based on the Issp/Ippp ratio, the orientation of CO relative to the macroscopic surface normal can be deduced, revealing the abundance of inclined/curved facets.

Polarization-dependent SFG measurements were carried out for two model catalyst systems, consisting of different metal nanoparticles (Pt vs. Pd), deposited by different methods (ALD vs. PVD), on different support materials (ZrO2 vs. Al2O3), with CO preferentially adsorbed on different binding sites (on-top vs. bridge), at different CO pressures (10 mbar vs. UHV) and different temperatures (425 vs. 200 K). In addition to the typically evaluated CO peak positions and SFG intensities, the polarization-dependent SFG measurements yielded Issp/Ippp ratios that reflect the nanoparticle morphology/surface curvature, in line with microscopic TEM and STM characterization. Even though SFG is usually not used for shape characterization, in situpolarization-dependent SFG allows observing changes upon treatments or during catalytic reactions (faceting, roughening, sintering etc.), while at the same time monitoring the reaction adsorbates/intermediates. This new approach may thus be utilized to characterize the morphology of model catalyst nanoparticles during preparation, pretreatment and catalytic reactions.

Original publication:

Polarization-dependent sum frequency generation (SFG) spectroscopy for in situ tracking of nanoparticle morphology

Verena Pramhaas, Holger Unterhalt, Hans-Joachim Freund, Günther Rupprechter

Angewandte Chemie International Edition, e202300230 (2023), opens an external URL in a new window


 Research supported by the Austrian Science Fund (FWF; I 4434-N and SFB TACO F81-P08).