No abstract

The sputtering of gold foil onto 1-n-butyl-3-methylimidazolium tetrafluoroborate, hexafluorophosphate, bis(trifluoromethylsulfonyl)amide, or tris(fluoro)tris(perfluoroethane)phosphate ionic liquids (ILs) generates stable and well-dispersed gold nanoparticles (NPs) of 3-5 nm under conditions of 40 mA, 335 V, and 2 Pa Ar work pressure. The size and size distribution of these Au nanoparticles depends on various experimental parameters, particularly the surface composition of the IL and less so the surface tension and viscosity. Under the experimental conditions used here, both nucleation and NP growth seem to occur on the IL surface and the NP size changes with the changes in the IL surface composition, especially with the increase of the fluorinated content. Moreover, the NP size is independent of sputtering time but does depend on the discharge current. When higher discharge currents are used, more gold atoms hit the ionic liquid surface per unit time, changing the kinetics of particle growth on the surface of the IL.

With the increased efforts in finding new energy storage systems for mobile and stationary applications, an intensively studied fuel molecule is dihydrogen owing to its energy content, and the possibility to store it in the form of hydridic and protic hydrogen, for example, in liquid organic hydrogen carriers. Here we show that water in the presence of paraformaldehyde or formaldehyde is suitable for molecular hydrogen storage, as these molecules form stable methanediol, which can be easily and selectively dehydrogenated forming hydrogen and carbon dioxide. In this system, both molecules are hydrogen sources, yielding a theoretical weight efficiency of 8.4% assuming one equivalent of water and one equivalent of formaldehyde. Thus it is potentially higher than formic acid (4.4 wt%), as even when technical aqueous formaldehyde (37 wt%) is used, the diluted methanediol solution has an efficiency of 5.0 wt%. The hydrogen can be efficiently generated in the presence of air using a ruthenium catalyst at low temperature.

The reduction of [Ru(COD)(2-methylallyl) 2 ] (COD ) 1,5-cyclooctadiene) dispersed in various room-temperature ionic liquids (ILs), namely, 1-n-butyl-3-methylimidazolium (BMI) and 1-n-decyl-3-methylimidazolium (DMI), associated with the N-bis(trifluoromethanesulfonyl)imidates (NTf 2 ) and the corresponding tetrafluoroborates (BF 4 ) with hydrogen gas (4 bar) at 50°C leads to well-dispersed immobilized nanoparticles. Transmission electron microscopy (TEM) analysis of the particles dispersed in the ionic liquid shows the presence of [Ru(0)] n nanoparticles (Ru-NPs) of 2.1-3.5 nm in diameter. Nanoparticles with a smaller mean diameter were obtained in the ILs containing the less coordinating anion (NTf 2 ) than that in the tetrafluoroborate analogues. The ruthenium nanoparticles in ionic liquids were used for liquid-liquid biphasic hydrogenation of arenes under mild reaction conditions (50-90°C and 4 bar). The apparent activation energy of E A ) 42.0 kJ mol -1 was estimated for the hydrogenation of toluene in the biphasic liquid-liquid system with Ru-NPs/BMI · NTf 2 . TEM analysis of the ionic liquid material after the hydrogenation reactions shows no significant agglomeration of the [Ru(0)] n nanoparticles. The catalyst ionic liquid phase can be reused several times without a significant loss in catalytic activity.