Tri‐salts added: Pt on alumina catalysts can be used for converting methanol and water into hydrogen and carbon dioxide (see picture), for applications such as hydrogen storage. Both the activity and selectivity could be enhanced by coating these materials with a thin layer of a molten salt mixture of Li/K/Cs acetate. Potassium doping was identified by DRIFTS measurements to be an important factor for the boost in catalyst performance.
In order to expand the temperature limits of Supported Ionic Liquid Phase (SILP) or Solid Catalyst with Ionic Liquid Layer (SCILL) systems to higher operation temperatures, the mixture of lithium acetate, potassium acetate, and caesium acetate (molar ratio of 0.2/0.275/0.525) has been studied in detail. Physico-chemical properties of the bulk melt are reported together with stability data of the modern salt on various solid support materials showing attractive properties for many potential high temperature applications.
The surface of macroscopic films
of the ternary molten salt mixture
Li0.2K0.275Cs0.525[OAc] has been
investigated by angle-resolved X-ray photoelectron spectroscopy (XPS)
as a function of temperature. With increasing temperature a preferential
depletion of K+ is observed by ∼40%. From temperature
programmed desorption we find that the onset for the cation desorption
follows the order Cs+, K+, and Li+, with activation energies of 125, 148, and 157 kJ mol–1, respectively; the corresponding value for the [OAc] anion is 147
kJ mol–1, which is, within the margin of error,
identical to the average of the value found for the cations. Ultrathin
films of the molten salt deposited on a Au(111) surface by physical
vapor deposition show preferential enrichment of Cs+, in
line with the lower activation energy and thus higher desorption rate
of Cs[OAc] from the ternary mixture. Angle-resolved XPS of the molten
salt/gold interface demonstrates that the first molten salt monolayer
grows in a layer-by-layer growth, followed by three-dimensional island
growth at higher coverages.
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