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