Ionic Liquid Interfaces

Ionic liquids (ILs) are salts with melting points below 100°C. Typically, they are charac­terized by an extremely low vapour pressure. Since their physical and chemical proper­ties can be tailored over a wide range, they represent a fascinating class of liquid materials with interesting applications in catalysis. Two important concepts in this context are Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL). In both, a high surface area solid substrate is covered with a thin IL film. In SILP, the film contains a homogeneously dissolved transition metal complex; in SCILL, the film modifies catalytically active surface sites at the support. The interfaces of the IL with the gas phase and with catalytic surfaces are thus of critical importance. They can be investigated in great detail under well-defined ultrahigh vacuum conditions using surface science methods like angle-resolved XPS, STM, AFM, molecular beams and MD calculations. Two examples will be discussed. The first addresses how the selectivity of hydrocarbon hydrogenation reactions can be tailored by an ultrathin IL film [1], and the second introduces the “buoy concept”, that is, the tailoring of the enrichment of metal complexes at the IL/vacuum interface [2].