CO2 is selectively hydrogenated to HCO2H or hydrocarbons (HCs) by RuFe nanoparticles (NPs) in ionic liquids (ILs) under mild reaction conditions. The generation of HCO2H occurs in ILs containing ...basic anions, whereas heavy HCs (up to C21 at 150 °C) are formed in the presence of ILs containing nonbasic anions. Remarkably, high values of TONs (400) and a TOF value of 23.52 h–1 for formic acid with a molar ratio of 2.03 per BMI·OAc IL were obtained. Moreover, these NPs exhibited outstanding abilities in the formation of long-chain HCs with efficient catalytic activity (12% conversion) in a BMI·NTf2 hydrophobic IL. The IL forms a cage around the NPs that controls the diffusion/residence time of the substrates, intermediates, and products. The distinct CO2 hydrogenation pathways (HCO2H or FT via RWGS) catalyzed by the RuFe alloy are directly related to the basicity and hydrophobicity of the IL ion pair (mainly imposed by the anion) and the composition of the metal alloy. The presence of Fe in the RuFe alloy provides enhanced catalytic performance via a metal dilution effect for the formation of HCO2H and via a synergistic effect for the generation of heavy HCs.
Confined water in aqueous solutions of imidazolium‐based ionic liquids (ILs) associated with acetate and imidazolate anions react reversibly with CO2 to yield bicarbonate. Three types of CO2 sorption ...in these “IL aqueous solutions” were observed: physical, CO2‐imidazolium adduct generation, and bicarbonate formation (up to 1.9 molbicarbonate mol−1 of IL), resulting in a 10:1 (molar ratio) total absorption of CO2 relative to imidazolate anions in the presence of water 1:1000 (IL/water). These sorption values are higher than the classical alkanol amines or even alkaline aqueous solutions under similar experimental conditions.
Trapped, but active: Aqueous solutions of ionic liquids (IL) with basic anions are employed for CO2 capture, resulting in higher values of sorption. The success of these experiments can be attributed to the occurrence of physical and chemical sorption, mainly owing to bicarbonate formation. Our detailed study shows that bicarbonate species are a result of the reversible reaction between water molecules trapped in the IL activated by the contact ion pair and CO2.
CO2 Electroreduction in Ionic Liquids Faggion, Deonildo; Gonçalves, Wellington D. G.; Dupont, Jairton
Frontiers in chemistry,
03/2019, Letnik:
7
Journal Article
Recenzirano
Odprti dostop
CO
2
electroreduction is among the most promising approaches used to transform this green-house gas into useful fuels and chemicals. Ionic liquids (ILs) have already proved to be the adequate media ...for CO
2
dissolution, activation, and stabilization of radical and ionic electrochemical active species in aqueous solutions. In general, IL electrolytes reduce the overpotential, increase the current density, and allow for the modulation of solution pH, driving product selectivity. However, little is known about the main role of these salts in the CO
2
reduction process the assumption that ILs form solvent-separated ions. However, most of the ILs in solution are better described as anisotropic fluids and display properties of an extended cooperative network of supramolecular species. That strongly reflects their mesoscopic and nanoscopic organization, inducing different processes in CO
2
reduction compared to those observed in classical electrolyte solutions. The major aspects concerning the relationship between the structural organization of ILs and the electrochemical reduction of CO
2
will be critically discussed considering selected recent examples.
A brief summary of selected pioneering and mechanistic contributions in the field of carbon-carbon cross-coupling reactions with palladium nanoparticles (Pd-NPs) in ionic liquids (ILs) is presented. ...Five exemplary model systems using the Pd-NPs/ILs approach are presented: Heck, Suzuki, Stille, Sonogashira and Ullmann reactions which all have in common the use of ionic liquids as reaction media and the use of palladium nanoparticles as reservoir for the catalytically active palladium species.
The role of small amounts of water in ionic liquids (ILs), namely, 1-n-butyl-2,3-dimethylimidazolium imidazolate (BMMI·Im), 2-methylimidazolate (BMMI·MeIm), and pyrazolate (BMMI·Pyr), is examined ...using NMR spectroscopy and density functional theory (DFT) calculations. The nuclear Overhauser effect (NOE) indicates that a water molecule is trapped inside the ionic network, keeping the ion pair in contact through strong H-bonds involving the hydrogen atoms of water and the nitrogen atoms of the IL anions to give a guest@host supramolecular structure. The formation of the H2O@IL pair complex with different ILs combined with the strong hydrogen bond strength within the complex is responsible for the selective H/D exchange reactions at the imidazolium C2-Me and ketone Cα positions.
The catalytic activity expressed by turnover number (TON) and turnover frequency (TOF) in different fields of catalysis (enzymatic, homogeneous (single‐site), heterogeneous (multi‐site), and ...nanocatalysis (oligo‐site)) are usually estimated in slightly different ways and with slightly different, yet important meanings. For soluble metal nanoparticles, the ideal is to determine the TON by using the titrated number of active catalytic sites before the catalyst is inactivated. However, in the absence of reliable titration methods it is suggested that TON figures should always be reported as the number of moles of reactants consumed per mol of soluble metal catalyst, and that they should also be corrected by the number of exposed surface atoms by using the metal atom’s magic number approach. Moreover, it is strongly recommended that the TOF should be determined from the slope of plots of turnover numbers versus time, because in various cases the size and shape of the soluble nanoparticles might change dramatically during the reaction. As in organometallic catalysis, in the absence of TON vs. time data, the TOF should be estimated for low substrate conversions.
Defects beat faces: It is proposed that, for soluble metal nanoparticles, ideally the turnover number (TON) is determined by using the titrated number of active catalytic sites. However, in the absence of reliable titration methods, the TON figures should be reported as the number of moles of reactants consumed per mol of soluble metal nanoparticle and the figures should also be corrected by the number of exposed surface atoms by using the metal atom's magic number approach.
The partial hydrogenation of benzene to cyclohexene is an economically interesting and technically challenging reaction. Over the last four decades, a lot of work has been dedicated to the ...development of an exploitable process and several approaches have been investigated. However, environmental constraints often represent a limit to their industrial application, making further research in this field necessary. The goal of this review is to highlight the main findings of the different disciplines involved in understanding the governing principles of this reaction from a sustainable chemistry standpoint. Special emphasis is given to ruthenium-catalyzed liquid phase batch hydrogenation of benzene.
Ceria (CeO2) is being increasingly used as support of metallic nanoparticles in catalysis due to its unique redox properties. Shedding light into the nature of the strong metal support interaction ...(SMSI) effect in CeO2-containing catalysts is important since it has a strong influence on the catalytic properties of the system. In this work, Cu/CeO2 and Ni/CeO2 nanoparticles are characterized when submitted to a reduction treatment at 500 °C in H2 atmosphere with a combination of in situ (XAS – X-ray absorption spectroscopy and time-resolved XAS) and ex situ (TEM – transmission electron microscopy and XPS - X-ray photoelectron spectroscopy) techniques. The existence of a capping layer decorating the Ni/CeO2 nanoparticles after the reduction treatment is shown, representing evidence for the SMSI effect. The kinetics of the SMSI occurrence is elucidated. It is proposed that the electronic factor of the SMSI effect has a strong influence on the reduction properties of the Ni nanoparticles supported on CeO2, decreasing its reduction temperature if compared to nonsupported Ni nanoparticles. The same phenomenon is not observed for Cu/CeO2 nanoparticles, where there is no evidence for the SMSI effect, and no changes on the reduction properties between supported and nonsupported Cu nanoparticles are observed.
Nitrogen‐, phosphorus‐, and sulfur‐containing palladacycles, typically containing four‐ or six‐electron donor anionic metallated ligands, are emerging as a new family of organometallic catalyst ...precursors. These thermally and air‐stable complexes are easy to handle and their synthesis is often straightforward. Palladacycles are now being successfully exploited in catalytic reactions ranging from classical hydrogenations to enantioselective aldol‐type condensations. The main recent achievements pertaining to their use in homogeneous organometallic catalysis are outlined herein.
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.
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