Exploring Electronic Effects in Selective Hydrogenation by (Ga,Sn)Pd2
Final Report Abstract
Within this ambitious project, the structural as well as electronic influences on the semihydrogenation of acetylene were addressed. This was realised by experimental and quantum chemical work conducted on polycrystalline as well as single-crystalline materials within the isostructural substitutional series Ga 1-x Sn x Pd2 . To cover the manifold questions and different approaches, the project team consisted of Prof. Armbrüster (TU Chemnitz), Prof. Grin (MPI CPfS) and Prof. Gille (LMU Munich) who´s project parts were funded by DFG. In addition, Prof. Gaudry, Dr. Fournée and Dr. Ledieu (IJL Nancy) contributed to the project by surface science investigations and surface DFT calculations without funding. During the project, additional XPS measurements became necessary which were conducted by Prof. Seyller (TU Chemnitz), thus enlarging the project team at no additional costs. Synthesis routes to single-phase materials in the ternary system were developed and the phase equilibria of Ga 1-x Sn x Pd2 , as far as relevant for the Czochralski growth of the singlecrystals, were established. Samples were thoroughly characterised concerning their elemental and phase composition, crystal structure and lattice parameters as well as crystallographic orientation and relative subgrain orientation in the case of the large single crystals. Based on the structural data, the electronic structure was calculated composition-dependent and clearly showed deviations from the expected ridged-band behaviour. Quantum chemical analysis of the chemical bonding resulted in homogenously distributed multi-centre bonds throughout the unit cell. Catalytic properties were determined for the full series, showing a strong dependence of the catalytic activity on the composition, thus the electronic structure, while the selectivity is independent of composition as would be expected due to the samples being isostructural (active-site isolation given for any composition). Concerning the activity, the observed volcano plot correlates strongly with the non-linear shift of the d-band centre in relation to the Fermi level. The validity of the correlation was further confirmed by near-ambient pressure XPS measurements, proving the stability of the compounds under reaction conditions (e.g. absence of hydride formation) and only a slight preference of Ga-segregation, thus maintaining the electronic change in the bulk also on the surface. Investigation of the structural effect required the surfaces-preparation of the single-crystalline slabs with different orientations in a reproducible way to conduct catalytic measurements. This turned out to be a proper challenge. Applying typically used polishing procedures leads to an amorphous Beilby layer on top of the single crystals, which annihilates any efforts to determine the catalytic properties of specific crystallographic orientations. Slightest differences in the polishing procedure (e.g. different operators) resulted in different Beilby layers, thus different catalytic properties. This could only be resolved in the last weeks of the project, so that the structural influences on the catalytic properties will be determined in the near future. Within the project, molecular adsorption by experiment (normal pressure as well as ultrahigh vacuum) and quantum chemical means was planned, but had to be sacrificed due to severe Corona restrictions at the involved partners. The restrictions also clearly showed that the discussion of complex scientific issues requires face-to-face meetings to have proper progress. In addition to the results obtained on the semi-hydrogenation of acetylene, this project resulted in a very valuable tool for the catalysis community, i.e. the platform material Ga 1-x Sn x Pd 2 . With this, structural and electronic influences in any reaction where the materials are stable can be addressed, allowing to study the effects systematically and reliably in a multitude of reactions (gas phase as well as electrochemistry).
Publications
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Intermetallic Compounds as Platform Materials in Heterogeneous Catalysis. 5th International Symposium of Institute for Catalysis, 2018, Sapporo
M. Armbrüster
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Revealing Electronic Influences in the Semihydrogenation of Acetylene. J. Phys. Chem. C 122, 2018, 21891
O. Matselko, R. R. Zimmermann, A. Ormeci, U. Burkhardt, R. Gladyshevskii, Y. Grin, M. Armbrüster
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Fixed-Bed Reactor for Catalytic Studies on Low-Surface Area Materials. Rev. Sci. Instrum. 90, 2019, 014101.
D.C.A. Ivarsson, I.G. Aviziotis, T. Keilhauer, M. Armbrüster
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Intermetallic Compounds – A Versatile Class of Materials Meets Interesting Catalytic Challenges, MRS Spring/Fall Meeting, 2020, online
M. Armbrüster
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Single Crystal Growth of Sn- and Ge-Substituted GaPd 2 for Basic Research in Catalysis Deutsche Kristallzüchtungstagung, 2020, München/Garching
S. Püschel, K. Bader, P. Gille
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Single Crystal Growth of Solid Solution from the Ga-Pd-Sn System for Basic Research in Heterogeneous Catalysis. J. Crystal Growth 532, 2020, 125401
K. Bader, A. Dorner, P. Gille
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Disentangling Electronic and Geometric Effects in Electrocatalysis Through Substitution in Isostructural Intermetallic Compounds. J. Am. Chem. Soc. 144, 2022, 8379
R. Zerdoumi, O. Matselko, L. Rößner, Yu. Grin, M. Armbrüster
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Properties of Bulk In-Pt Intermetallic Compounds in Methanol Steam Reforming. ChemPhysChem 23, 2022, e20220007
N. Köwitsch, S. Barth, K. Ploner, R. Blume, D. Teschner, S. Penner, M. Armbrüster
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Reliable Crosshairs for Catalyst Development ACS Spring Meeting, 2022, San Diego/online
M. Armbrüster
