ABSTRACT
Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C4 C1 Im][PF6 ] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our previous angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5 %mol down to 1 %mol and present complementary surface tension pendant drop (PD) measurements under ultraclean vacuum conditions. This combination allows for connecting the microscopic information on the IL/gas interface derived from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1 %mol . It also displays a strong temperature dependence, which was not observed for 5 %mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of IL-based catalyst systems with large contact areas to the surrounding reactant/product phase, such as in supported IL phase (SILP) catalysis.
ABSTRACT
Invited for the cover of this issue are the groups of Hans-Peterâ Steinrück and Peterâ Wasserscheid at the Friedrich-Alexander-Universität Erlangen-Nürnberg. The image depicts two Pt catalysts dissolved in an ionic liquid. For one of them, fluorinated side chains in the ligand system act as buoys leading to pronounced enrichment of the complex at the gas/IL interface, as is evidenced by strongly enhanced Pt signals in angle-resolved photoelectron spectroscopy. For the complex without fluorinated side chains, no such effect is observed. Read the full text of the article at 10.1002/chem.202203325.
ABSTRACT
The targeted enrichment of a Pt complex with an ionic liquid (IL)-derived ligand system in IL solution is demonstrated by using angle-resolved X-ray photoelectron spectroscopy. When the ligand system is complemented with fluorinated side chains, the complex accumulates strongly at the IL/gas interface, while in an equivalent solution of a complex without these substituents no such effect could be observed. This buoy-like behavior induces strong population of the complex at the outermost molecular layer close to surface saturation, which was studied over a range from 5 to 30 %mol . The surface enrichment was found to be most efficient at the lowest concentration, which is particularly favorable for catalytic applications such as supported ionic-liquid-phase (SILP) catalysis.
