Semi-hydrogenation of Acetylene on Intermetallic Compounds

Selective semi-hydrogenation of acetylene in ethylene feedstock represents an industrially important reaction in the preparation of polyethylene (> 80 Mt/a). Industrially, Pd-based catalysts are used, but the catalysts are suffering from their low stability. Through our innovative and knowledge-based implementation of site isolation concepts by means of structurally ordered intermetallic compounds, we are able to generate active, selective, and stable catalyst materials (see Fig. 1)¹. The used compounds, Pd₃Ga₇, PdGa and Pd₂Ga, show ordered crystal structures, in which the Pd atoms exist as dumbbells isolated or as 3D networks. In all cases, the Pd-Pd coordination number is significantly reduced compared to the element. Because of the lower complexity of unsupported intermetallic compounds and their in situ stability, our approach allowed a knowledge-based development of heterogeneous catalyst systems and led to the discovery of a noble-metal-free hydrogenation catalyst, Al-Fe, which shows the same activity, selectivity, and stability as with Ga-Pd compounds.²

Figure1:Catalytic properties of Ga-Pd intermetallic compounds compared to Pd/Al2O3. Gas composition of 50 % C2H4, 5% H2, 0,5% C2H2 in He.

 

1. M. Armbrüster, K. Kovnir, M. Behrens, D. Teschner, Yu. Grin, R. Schlögl, J. Am. Chem. Soc. 132, 2010, 14745. doi: 10.1021/ja106568t
2. M. Armbrüster, K. Kovnir, M. Friedrich, D. Teschner, G. Wowsnick, M. Hahne, P. Gille, L. Szentmiklósi, M. Feuerbacher, M. Heggen, F. Girgsdies, D. Rosenthal,R. Schlögl, Yu. Grin, Nature Mater. 11, 2012, 690. doi:10.1038/nmat3347