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A. Motin, A. Steiger-Thirsfeld, M. Stöger-Pollach, G. Rupprechter:
"Model Catalysis with HOPG‑Supported Pd Nanoparticles and Pd Foil: XPS, STM and C2H4 Hydrogenation";
Catalysis Letters, 1 (2021), 1.

A surface science based approach was applied to model carbon supported Pd nanoparticle catalysts. Employing physical
vapour deposition of Pd on sputtered surfaces of highly oriented pyrolytic graphite (HOPG), model catalysts were prepared
that are well-suited for characterization by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy
(STM). Analysis of the HOPG substrate before and after ion-bombardment, and of Pd/HOPG before and after annealing,
revealed the number of "nominal" HOPG defects (~ 1014
cm−
2) as well as the nucleation density (~ 1012
cm−
2) and structural
characteristics of the Pd nanoparticles (mean size/height/distribution). Two model systems were stabilized by UHV annealing
to 300 °C, with mean Pd particles sizes of 4.3 and 6.8 nm and size/height aspect ratio up to ~ 10. A UHV-compatible flow
microreactor and gas chromatography were used to determine the catalytic performance of Pd/HOPG in ethylene (
C2H4)
hydrogenation up to 150 °C under atmospheric pressure, yielding temperature-dependent conversion values, turnover frequencies
(TOFs) and activation energies. The performance of Pd nanocatalysts is compared to that of polycrystalline Pd foil
and contrasted to Pt/HOPG and Pt foil, pointing to a beneficial effect of the metal/carbon phase boundary, reflected by up to
10 kJ mol−
1 lower activation energies for supported nanoparticles.

http://dx.doi.org/10.1007/s10562-021-03868-2