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Intermetallic Compounds – Materials for a Knowledge-Based Development in Heterogeneous Catalysis

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Development in heterogeneous catalysis is often hindered by the complexity of the applied catalytic systems. While this is necessary for industrial use to maximise the surface area and stability, a valuable basic science approach is to make the catalysts “as simple as possible, but not simpler” (A. Einstein). A class of compounds not often investigated in catalysis are intermetallic compounds, which differ strongly from substitutional alloys, since they possess crystal structures different from the constituent elements. [1] The more complicated structures – extreme cases are quasicrystalline compounds, the discovery of which has been awarded the Noble price in chemistry 2011 – result from the partly covalent bonding within the compounds, which also enhances their stability leading to high stability under reaction conditions and reduced segregation. The structural changes and the bonding situation result in much stronger changes of the electronic structure compared to substitutional alloys.

Combining the “as simple as possible, but not simpler” idea with the huge potential of the intermetallic compounds leads to their unsupported use in heterogeneous catalysis. Due to their large number (more than 10,000 binary intermetallic compounds are known and many more with more than two elements) this opens a vast matrix to explore relationships between electronic and crystal structure on the one hand and the catalytic properties on the other. Uncovering these relationships leads to a deep understanding and the gained knowledge can be used to select intermetallic compounds with optimised crystal and electronic structure in the next step. This approach leads to a knowledge-based development and is named the knowledge-based approach. [2] This approach has been successfully applied in the development of a new class of highly selective semi-hydrogenation catalysts based on Ga-Pd intermetallic compounds. These compounds represent the first example, where the knowledge-based approach was applied starting from the bulk materials, [2-5] studying their stability under reaction conditions, [5,6] developing an approach to unsupported nanoparticu- late materials [7] and inventing an industrially feasible route to highly active materials while preserving the selectivity and stability of the bulk compounds. [8] Due to the knowledge gained during the investigations, the Pd-based systems could finally be replaced by more ubiquitous non-noble metal based materials. [9]

[1] H. Kohlmann, in Encycl. of Physical Science and Technology, 3 rd ed., Vol. 9, 2002, Academic Press.

[2] K. Kovnir, M. Armbrüster, D. Teschner, T.V. Venkov, F.C. Jentoft, A. Knop-Gericke, Yu. Grin, R. Schlögl, Sci. Technol. Adv. Mater. 8, 2007, 420.

[3] J. Osswald, K. Kovnir, M. Armbrüster, R. Giedigkeit, R.E. Jentoft, U. Wild, Yu. Grin, R. Schlögl, J. Catal. 258, 2008, 219.

[4] K. Kovnir, J. Osswald, M. Armbrüster, R. Giedigkeit, T. Ressler, Yu. Grin, R. Schlögl, Stud. Surf. Sci. Catal. 162, 2006, 481.

[5] M. Armbrüster, K. Kovnir, M. Behrens, D. Teschner, Yu. Grin, R. Schlögl, J. Am. Chem. Soc. 132, 2010, 14745-14747.

[6] J. Osswald, R. Giedigkeit, R.E. Jentoft, M. Armbrüster, F. Girgsdies, K. Kovnir, T. Ressler, Yu. Grin, R. Schlögl, J. Catal. 258, 2008, 210.

[7] K. Kovnir, M. Armbrüster, D. Teschner, T.V. Venkov, L. Szentmiklósi, F.C. Jentoft, A. Knop-Gericke, Yu. Grin, R. Schlögl, Surf. Sci. 603, 2009, 1784.

[8] M. Armbrüster, G. Wowsnick, M. Friedrich, M. Heggen, R. Cardoso-Gil, J. Am. Chem. Soc. 133, 2011, 9112.

[9] A. Ota, M. Armbrüster, M. Behrens, D. Rosenthal, M. Friedrich, I. Kasatkin, F. Girgsdies, W. Zhang, R. Wagner, R. Schlögl, J. Phys. Chem. C 115 , 2011, 1368.

[10] M. Armbrüster, K. Kovnir, Yu. Grin, R. Schlögl, P. Gille, M. Heggen, M. Feuerbacher, PCT /EP2010/053682, 2010.

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