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Dynamics of Palladium and Palladium-Gold Thin-Film Catalysts during Acetylene Semihydrogenation Revealed by Synchrotron Grazing Incidence X-ray Diffraction

Gili A, Thum L, Khodabakhshi M, Shivam S, Garcia-Diez R, Bär M, Wollgarten M, Schlatmann R, Amkreutz D (2025)

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Publication Type: Journal article

Publication year: 2025

Journal

DOI: 10.1021/acs.jpcc.5c02040

Abstract

Catalytic thin films are an exciting concept in the field of heterogeneous catalysis that produce 2D structures with precisely engineered active sites to generate fundamental knowledge and optimize catalytic performance. Acetylene semihydrogenation on Pd catalysts is an industrially crucial chemical reaction known for its complex subsurface chemistry: competitive occupation of the metal’s interstitials between atomic hydrogen and carbon leads to substantial changes in reaction selectivity, the key performance indicator. In the present work, we monitor the dynamics of supported thin films of Pd and PdAu during the reaction using a combination of synchrotron in situ GIXRD, pre- and post-reaction XPS and TEM. PdHx formation occurs at room temperature, with a significant increase in the lattice parameter (2.9-4.1%) for Pd, whereas PdAu only marginally expands (0.4%) upon interaction with molecular H2. Changes in the partial pressure of H2 result in differences in the formation of PdHα and/or PdHβ. At a partial pressure of 0.1 bar, both the α and β phases coexist in the 20 nm Pd film. The extreme sensitivity of the in situ GIXRD approach allows to monitor the transition from Pd(metallic) → PdHα → PdHβ, its reversibility, and the stability of the films upon cycles of H2. Exposure to C2H2 alone or mixtures of C2H2:H2 at elevated temperatures results in the irreversible expansion of the Pd unit cell (2.5-3.5%), demonstrating the formation of a PdCx interstitial solution (with homogeneous composition along the thickness of Pd), which hinders almost completely later hydride formation. PdAu forms an interstitial solution with C, although to a much lesser extent than that of the Pd films. The current work generates fundamental knowledge using thin-film catalysts, which represent a step between model and industrial systems. Our experiments close the pressure gap compared to previous experiments performed with ideal surfaces at very low pressures and allow to monitor the competitive dynamics of PdHx and PdCx formation in the catalytic subsurface.

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APA:

Gili, A., Thum, L., Khodabakhshi, M., Shivam, S., Garcia-Diez, R., Bär, M.,... Amkreutz, D. (2025). Dynamics of Palladium and Palladium-Gold Thin-Film Catalysts during Acetylene Semihydrogenation Revealed by Synchrotron Grazing Incidence X-ray Diffraction. Journal of Physical Chemistry C. https://doi.org/10.1021/acs.jpcc.5c02040

MLA:

Gili, Albert, et al. "Dynamics of Palladium and Palladium-Gold Thin-Film Catalysts during Acetylene Semihydrogenation Revealed by Synchrotron Grazing Incidence X-ray Diffraction." Journal of Physical Chemistry C (2025).

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