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Start of funding 01.01.2011

Characterization of Supported Ionic Liquid Phase (SILP) catalysts by in-situ spectroscopy methods and catalytic experiments

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Supported Ionic Liquid Phase (SILP) catalysts are new hybrid materials composed of three major components: an ionic liquid film, a metal catalyst dissolved therein, and a porous solid to support this ionic catalyst film. Thus, SILP catalysts combine the advantages of both, homogeneous and heterogeneous catalysis. The material appears macroscopically as a solid while it behaves microscopically like a molecular defined and homogeneously dissolved catalyst. This project aims on understanding the structure and texture of the ionic liquid film by means of in-situ spectroscopical methods such as FT-IR or DRIFTS and ex-situ methods like MAS-NMR. Additionally catalytic experiments will be performed to gain kinetic performance data.

Final report:
The joint BaCaTec project on characterization of SILP materials between Prof. Alexis T. Bell (University of California – Berkeley) and Prof. Peter Wasserscheid (University Erlangen) was supported from January 1st 2011 until June 30th 2012. As originally proposed, detailed FTIR measurements under in-situ conditions and solid state NMR measurements were carried out and led to novel insights into the structure of the liquid film inside the porous materials. Results from these measurements suggest that active Rh centers are not present as homogeneous complexes dissolved in an ionic liquid film as previously speculated, but are rather present as HRh(CO)2(SX) complexes bound to the support by interactions of the sulfonate groups of SX with silanol groups of the support. This observation led to the conclusion that one important function of the ionic liquid is to inhibit undesired interactions of SX ligands, since such interactions render the phosphine groups unavailable for interaction with the Rh metal center (Shylesh et al. 2012). Additional catalytic tests with regards to mechanistic investigations led to detailed understanding of the rate determining step. It was found, that depending on reaction temperature selectivity, partial reaction orders and activation energies were altered. This could be linked to the free energy of activation in the rate determining step of the catalytic cycle (Hanna et al. 2012). Using solid-state NMR techniques the ionic liquid film formation and distribution in the porous catalysts was monitored. It was deduced that at low ionic liquid loadings islands seemed to be formed with particular interaction between the protons of the ionic liquid and the support’s silanol groups. Increasing the ionic liquid loading led to a uniform coverage with bulk-like properties. These findings were in good agreement with catalytic activities of comparable SILP materials (Haumann et al. 2012).

Publications:

• S. Shylesh, D. G. Hanna, S. Werner, A. T. Bell, ACS Catal. 2012, 2(4), 487-493.
• D. G. Hanna, S. Shylesh, S. Werner, A. T. Bell, J. Catal. 2012, 292, 166-172.
• M. Haumann, A. Schönweiz, H. Breitzke, G. Buntkowsky, S. Werner, N. Szesni, Chem. Eng. Technol. 2012, 35(8), 1421-1426U.