A study published in Nanoscale by researchers from Tokyo Metropolitan University investigated the adsorption of hydrogen and carbon monoxide in a solid with a crown-motif structure composed of platinum and gold.
They tested [PtAu8(PPh3)8]-H[PMo12O40], referred to as PtAu8-PMo12, using rapid X-ray absorption measurements and theoretical calculations. Their findings indicate that the dimensions of nanoscale voids within the structure significantly influence gas adsorption, emphasizing the importance of void design in materials for next-generation sensors and gas separation technologies.
Ligand-protected metal clusters have gained attention in materials research due to their unique catalytic properties and distinct geometries compared to bulk metals. Platinum-containing clusters, in particular, have been studied for their role in the hydrogen evolution reaction (HER), which produces hydrogen. Understanding gas transport in metal cluster-based materials is essential for optimizing their performance.
Under the direction of Professor Seiji Yamazoe, the researchers examined a crown-motif structure in which a platinum atom is positioned above a ring of eight gold atoms. The platinum-gold cluster was stabilized by phosphine ligands and incorporated into a crystalline framework. The study aimed to analyze how gas molecules interact with a solid rich in platinum atoms, which are known for their strong gas-binding capabilities.
Using quick-scan X-ray absorption spectroscopy at 0.1-second intervals, the team monitored the adsorption of hydrogen and carbon monoxide in PtAu8-PMo12, tracking microscopic structural changes in response to gas exposure. Both gases effectively bound to the platinum atom, altering its electronic state and surrounding atomic structure. Hydrogen was found to adsorb more rapidly than carbon monoxide and in a reversible manner.
Experimental observations and theoretical calculations indicate that hydrogen’s smaller molecular size enables faster diffusion through the ultrathin channels connecting the voids in PtAu8-PMo12. In contrast, carbon monoxide exhibited irreversible binding to platinum atoms. The interaction was strong enough, and the voids were small enough, that structural distortion occurred, transforming the crown-motif into a chalice-like configuration, with the platinum atom shifting deeper into the structure.
This study contributes to a broader effort to understand structural reprogramming in chemical compounds. The findings highlight the role of diffusion in nanoscale voids as a key factor in structural transformations and gas transport in solids.
The research was supported by a NEDO Project (JPNP14004), JSPS KAKENHI (Grant Numbers 22K14543, 24K01259, 24K17562, 24H02210, 24H02211, and 24H02217), a Tokyo Metropolitan Government Advanced Research Grant (R3-1), the Tokyo Human Resources Fund for City Diplomacy, and the Tokyo Metropolitan University Research Fund for Young Scientists.
Synchrotron radiation experiments were conducted at SPring-8 with approval from the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Numbers 202407, 2023A1326, 2022B1259, and 2021B1380).
Journal Reference:
Matsuyama, T. et. al. (2024) In situ QXAFS study of CO and H2 adsorption on Pt in [PtAu8(PPh3)8]-H[PMo12O40] solid. Nanoscale. doi.org/10.1039/D4NR03785E
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