Forging stable catalysts for the future

Noble metal catalysts are critical ingredients in reactions for large-scale chemical synthesis, environmental energy generation and air purification. Research from Friedrich-Alexander University Erlangen-Nürnberg (FAU) with MAX IV’s HIPPIE beamline outlines a unique single atom catalyst (SAC) model system based on platinum-gallium liquid metal solution or SCALMS.

HIPPIE beamline at MAX IV Laboratory.

The FAU research group studied the stability of the model system under ultra-high vacuum and at near-ambient pressure at different temperatures. The study combined polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) methods. For PM-IRAS, carbon monoxide was utilized as a probe to obtain data on surface structure, composition, and morphology of the system.

The question of thermal stability is an important one for practical application of single atom catalysts (SACs). The SCALMS concept allows preparation of SACs where platinum acts as the active species. Research of SAC systems has enjoyed significant focus in recent years due to their capacity to catalyse a reaction with individual active atoms, instead of nanoparticles. Thus, improving the efficient utilization of costly noble metals in catalysis.

The SCALMS model system consists of platinum-gallium (Pt-Ga) alloy with low Pt/Ga ratio. It was prepared with physical vapor deposition of Pt and Ga on highly oriented pyrolytic graphite (HOPG), a non-metallic substrate that enables acquisition of high-quality IR data in reflection geometry. The adsorption of carbon monoxide allowed observation of changes in the surface composition and morphology during the thermal treatments. The simultaneous measurements of PM-IRAS and NAP-XPS were carried out at HIPPIE beamline at MAX IV.

In previous studies, SCALMS systems have proven successful in alkane dehydrogenation reactions, with results suggesting that SCALMS catalysts are less prone to deactivation. The FAU study provides new knowledge of nanoparticle stability, agglomeration mechanisms, and substrate-deposit interplay, and paves the way for development of more durable SCALMS-based single atom catalysts.

Publication

Chantal Hohner, Miroslav Kettner, Corinna Stumm, Dominik Blaumeiser, Haiko Wittkämper, Mathias Grabau, Matthias Schwarz, Christian Schuschke, Yaroslava Lykhach, Christian Papp, Hans-Peter Steinrück, and Jörg Libuda. Pt–Ga Model SCALMS on Modified HOPG: Thermal Behavior and Stability in UHV and under Near-Ambient Conditions. The Journal of Physical Chemistry C 2020 124 (4), 2562-2573 DOI: 10.1021/acs.jpcc.9b10944

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