Ionic liquids (ILs) are salts with melting points below 100 °C, which are characterized by an extremely low vapour pressure. Their physical and chemical properties can be tailored over a wide range, and they therefore represent a fascinating class of liquid materials with interesting applications in catalysis. One important example is the Solid Catalyst with Ionic Liquid Layer (SCILL) approach, which is already used in large-scale for hydrogenation reactions. In SCILL, a heterogeneous catalyst, immobilized on a solid support, is impregnated with an IL layer to enhance selectivity and product yields. To further improve this approach, a molecular level understanding of the specific IL/catalyst interactions is required, which can be obtained from UHV-based surface science studies of model systems. This knowledge then allows for tailoring the interface in real SCILL systems. We recently characterized the adsorption of ultrathin layers of the IL 1,3 dimethylimidazolium bis(trifluoromethanesulfonyl) imide ([C₁C₁Im][Tf₂N]) on Pt(111) by XPS and STM [1]. Moreover, using molecular beam methods and MD calculations we demonstrated how the adsorption dynamics of 1,3-butadiene and 1-butene on Pt(111) can be modified by a thin IL film [2]: We observed that increasing the IL coverage leads to an increased blocking of adsorption sites for both olefins. Interestingly, a smaller amount of IL is needed to prevent 1-butene adsorption as compared to 1,3-butadiene adsorption, which we propose to be directly related to the IL’s influence on selective hydrogenation in SCILL catalysis.

Funding was received through SFB 1452 "Catalysis at Liquid Interfaces".

[1]   S. Massicot et al, Adsorption and Thermal Evolution of [C₁C₁Im][Tf₂N] on Pt(111), Phys.Chem.Chem.Phys. 25 (2023) 27953-27966.
[2]   L. Winter et al, Tailoring the Selectivity of 1,3-Butadiene versus 1-Butene Adsorption on Pt(111) by Ultrathin Ionic Liquid Films, ACS Catalysis 13 (2023) 10866-10877.