Florian T. U. Kohler

Continuous gas-phase desulfurisation using supported ionic liquid phase (SILP) materials

Supported ionic liquid phase (SILP) materials have been developed for a continuous gas cleaning process. The technology is exemplified for the desulfurisation of a model gas stream consisting of 500 ppmwt n-butyl mercaptan in n-heptane vapour to levels of mercaptan below 5 ppmwt. By varying the ionic liquid structure, acidity and loading, [C12MIM]Cl/SnCl2 (XSnCl2 = 0.50) on alumina in an ionic liquid loading of 20 vol% of the supports pore volume was identified as a particularly suitable gas sorption system. Breakthrough experiments demonstrate desulfurisation performance of up to 130 h time-on-stream, and the suitability of the system for loading/unloading cycles in a pressure and temperature swing operation mode.

Carbon nanohorn-based electrolyte for dye-sensitized solar cells

For the first time, carbon nanohorns were implemented into solid-state electrolytes for highly efficient solid-state and quasi-solid-state DSSCs. They feature an effective catalytic behavior towards the reduction of I3− and enhance the I3− diffusivity in the electrolyte. In a final device, solar cells with 7.84% efficiency at room temperature were achieved. As a matter of fact, this is the highest reported efficiency for nanocarbon-based electrolytes up to date.

Long-alkyl-chain-derivatized imidazolium salts and ionic liquid crystals with tailor-made properties

A series of new 1,3-dialkylimidazolium salts with the general formula [CnCnIM][A] (for n = 12; A = PF6−, OTf−, NTf2−; for n = 10, 14, 16, and 18; A = BF4−, ClO4−) has been synthesized. The [C12C12IM][A] salts are ionic liquids at room temperature, whereas all [CnCnIM][BF4] and [CnCnIM][ClO4] (n = 10, 14, 16, 18) salts demonstrate a liquid crystalline phase at elevated temperatures that have a large mesophase window, which varies from 10 to 80 °C with increasing alkyl chain length. In particular, [C10C10IM][BF4] shows liquid crystalline behavior at room temperature and therefore is potentially suitable for application as a pre-organized reaction medium in synthesis and catalysis. Viscosity studies of [C16C16IM][BF4] and the corresponding perchlorate salt demonstrate strong non-Newtonian viscosity behavior for the liquid crystalline state of these ionic liquids.

Ethylene to 2-Butene in a Continuous Gas Phase Reaction using SILP-Type Cationic Nickel Catalysts

Owing to shifting market demands, it is important to convert ethylene to propylene. One attractive way to achieve this conversion is the dimerization of ethylene to 1‐butene, followed by isomerization to 2‐butene and subsequent metathesis of 2‐butene/ethylene olefin. Our contribution focuses on combining the first two steps. Herein, we report a highly selective tandem dimerization/isomerization of ethylene to 2‐butene catalyzed by homogeneously dissolved cationic nickel complexes. These catalysts can be efficiently immobilized by using the supported ionic liquid phase technology. Such supported ionic liquid phase materials have been tested under continuous gas phase conditions and demonstrated attractive catalytic performance with respect to both catalyst stability and productivity after the optimization of support, ionic liquid, ligand, and process parameters. The limited thermal stability of the nickel complexes and olefin condensation at too low temperatures require a careful thermal management of the fixed‐bed reactor.

Supported ionic liquid phase (SILP) materials for removal of hazardous gas compounds – efficient and irreversible NH3 adsorption

Novel supported ionic liquid phase (SILP) gas purification materials have been developed to remove ammonia irreversibly from an ambient gas flow of nitrogen (1000 ppm NH3 in N2, wet and dry). In the applied SILP materials, thin films of imidazolium based ionic liquids and ionic solutions of metal complexes, namely [C8C1Im][NTf2], [C8C1Im][NTf2]/Cu(NTf2)2, [C8C1Im][NTf2]/Co(NTf2)2 and [CnC1Im]Cl/CuCl2 (n = 2, 4, 8), were dispersed onto the large surface area of polymer-based spherical activated carbon supports. For the [CnC1Im]Cl/CuCl2 (n = 2, 4, 8) based SILP materials the use of a humid gas flow significantly enhances NH3 absorption as demonstrated by a clear increase of breakthrough times. The irreversibility of the ammonia sorption and the broadband capability (e.g. Cl2, H2S and cyclohexane) of the prepared SILP absorber materials are reported and compared to typical standards for gas purification adsorber materials (ABEK regulations).

Functional nickel complexes of N-heterocyclic carbene ligands in pre-organized and supported thin film materials

Nickel(II) complexes with double alkyl chain functionalized N-heterocyclic carbene (NHC) ligands, [NiCl2(C12MIM)2] and [NiCl2(C12C12IM)2], where C12MIM = 1-dodecyl-3-methylimidazolin-2-ylidene (1) and C12C12IM = 1,3-didodecylimidazolin-2-ylidene (2), have been prepared and fully characterized by 1H NMR, 13C NMR, and CHN elemental analyses. Furthermore, we have developed a system, in which double long alkyl chain derivatized Ni–NHC complexes are dissolved in the related ionic liquid crystalline 1,3-didodecylimidazolium tetrafluoroborate, [C12C12IM][BF4], to form pre-organized structures for enhanced reactivity. Remarkably, differential scanning calorimetry, polarized optical microscopy, and temperature-programmed IR reflection absorption spectroscopy performed on a mixture of 10 wt% Ni complexes in [C12C12IM][BF4] demonstrate that this system retains an ionic liquid crystalline phase; even after immobilization onto a silica-100 support with pore filling α = 1.

Temperature‐Dependent Surface‐Enrichment Effects of Imidazolium‐Based Ionic Liquids

We present the first systematic study of the influence of temperature on the degree of surface enrichment of 1-alkyl-3-methylimidazolium-based ionic liquids (ILs). Using angle-resolved X-ray photoelectron spectroscopy, we demonstrate that the degree of surface enrichment strongly decreases with increasing temperature for all the studied ILs. For ILs with the same cation, but different anions, [C8 C1 Im]Br, [C8 C1 Im][TfO] and [C8 C1 Im][Tf2 N], no significant differences of the temperature-induced partial loss of surface enrichment are found. Measurements for [C4 C1 Im][TfO], [C8 C1 Im][TfO] and [C18 C1 Im][TfO] indicate a small effect of the chain length. For [C18 C1 Im][TfO], a continuous decrease of alkyl surface enrichment is found with increasing temperature, with no abrupt changes at the phase-transition temperature from the smectic A to the isotropic phase, indicating that the surface enrichment is not affected by this phase transition.

Dimerization of ethene in a fluidized bed reactor using Ni-based Supported Ionic Liquid Phase (SILP) catalysts

The complexes [(mall)Ni(dppanis)][SbF6] (mall = methallyl, dppanis = (2-methoxyphenyl)diphenylphosphine) 1, [(mall)Ni(PPh3OC10)][SbF6] (PPh3OC10 = (2-decyloxyphenyl)diphenylphosphine) 2, and [(mall)Ni(PPh3OdiMePh)][SbF6] (PPh3OdiMePh = (2-(2,6-dimethylphenoxy)phenyl)diphenylphosphine) 3 were immobilized as Supported Ionic Liquid Phase (SILP) catalysts and applied for the tandem dimerization/isomerization of ethylene to 2-butene in a fluidized bed reactor. The better heat removal in the fluidized bed improves the catalyst stability and allows for a more detailed investigation of the deactivation mechanism. Based on kinetic studies, a second order deactivation mechanism is proposed, in which two nickel complexes dimerize if the supply of ethene is insufficient.