A General One-Pot Methodology for the Preparation of Mono- and Bimetallic Nanoparticles Supported on Carbon Nanotubes: Application in the Semi-hydrogenation of Alkynes and Acetylene.

A facile and straightforward methodology for the preparation of monometallic (copper and palladium) and bimetallic nanocatalysts (NiCu and PdCu) stabilized by a N-heterocyclic carbene ligand is reported. Both colloidal and supported nanoparticles (NPs) on carbon nanotubes (CNTs) were prepared in a one-pot synthesis with outstanding control on their size, morphology and composition. These catalysts were evaluated in the selective hydrogenation of alkynes and alkynols. PdCu/CNTs revealed an efficient catalytic system providing high selectivity in the hydrogenation of terminal and internal alkynes. Moreover, this catalyst was tested in the semi-hydrogenation of acetylene in industrially relevant acetylene/ethylene-rich model gas feeds and showed excellent stability even after 40 h of reaction.

Tunneling effects in confined gold nanoparticle hydrogenation catalysts.

Clean surface gold nanoparticles (AuNPs) of ∼6.6 nm that were confined in ionic liquid (IL) cages of hybrid γ-alumina (γ-Al2O3) displayed hydrogenation pathways in the reduction of trans-cinnamaldehyde distinct from those imprinted directly onto γ-Al2O3. Hydrogen activation proceeded via homolytic activation in IL-encapsulated AuNPs and via heterolytic cleavage for IL-free supported AuNPs. Higher negative apparent entropy (ΔSapp) values were obtained for the IL-confined AuNPs compared to the non-hybrid catalyst (Au/γ-Al2O3), suggesting a decrease in the number of microstates induced by the nano-confined environment. High kinetic isotope effect (KIE) values (kH/kD = 2.5-2.9 at 273 K) and Arrhenius convex curves were observed. Furthermore, differences of 5.6 and 6.2 kJ mol-1 between the apparent activation energies of the deuteration and hydrogenation reactions (E-E) associated with pre-exponential factor ratios (AD/AH) of 4.6 and 5.1 provided strong evidence of the possible involvement of a tunneling pathway in the case of the confined AuNPs.

Hydrophobic effects on supported ionic liquid phase Pd nanoparticle hydrogenation catalysts.

Hybrid organosilicas prepared by sol-gel processes using 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions can be easily decorated with well dispersed and similar size (1.8-2.1 nm) Pd nanoparticles (Pd-NPs) by simple sputtering-deposition. Higher Pd concentration at the surface compared to the deeper region is obtained in the supports with smaller pore diameter (containing hydrophobic ILs) than in supports with the largest pore diameter (containing hydrophilic ILs). The IL hydrophobicity plays a central role in the hydrogenation of dienes by controlling the diene access to NP surface active sites.

Interplay between cationic and neutral species in the rhodium-catalyzed hydroaminomethylation reaction.

The reactivity of [Rh(CO)(2){(R,R)-Ph-BPE}]BF(4) (2) toward amine, CO and/or H(2) was examined by high-pressure NMR and IR spectroscopy. The two cationic pentacoordinated species [Rh(CO)(3) {(R,R)-Ph-BPE}]BF(4) (4) and [Rh(CO)(2)(NHC(5)H(10)){(R,R)-Ph-BPE}]BF(4) (8) were identified. The transformation of 2 into the neutral complex [RhH(CO)(2){(R,R)-Ph-BPE}] (3) under hydroaminomethylation conditions (CO/H(2), amine) was investigated. The full mechanisms related to the formation of 3, 4 and 8 starting from 2 are supported by DFT calculations. In particular, the pathway from 2 to 3 revealed the deprotonation by the amine of the dihydride species [Rh(H)(2)(CO)(2){(R,R)-Ph-BPE}]BF(4) (6), resulting from the oxidative addition of H(2) on 2.

Supported Imidazolium-Based Ionic Liquids on a Polysulfone Matrix for Enhanced CO2 Capture.

The present work demonstrates the potential for improved CO2 capture capabilities of ionic liquids (ILs) by supporting them on a polysulfone polymeric matrix. CO2 is one of the main gases responsible for the greenhouse effect and is a focus of The European Commission, which committed to diminishing its emission to 55% by 2023. Various ILs based on combinations of 1-butyl-3-methyl- imidazolium cations and different anions (BMI·X) were synthesized and supported on a polysulfone porous membrane. The influence of the membrane structure and the nature of ILs on the CO2 capture abilities were investigated. It was found that the membrane's internal morphology and its surface characteristics influence its ILs sorption capacity and CO2 solubility. In most of the studied configurations, supporting ILs on porous structures increased their contact surface and gas adsorption compared to the bulk ILs. The phenomenon was strongly pronounced in the case of ILs of high viscosity, where supporting them on porous structures resulted in a CO2 solubility value increase of 10×. Finally, the highest CO2 solubility value (0.24 molCO2/molIL) was obtained with membranes bearing supported ILs containing dicarboxylate anion (BMI.MAL).

Synergism between iron porphyrin and dicationic ionic liquids: tandem CO2 electroreduction-carbonylation reactions.

Here, we report a simple procedure that drastically reduces the electrochemical E(FeI/Fe0) and E0cat of the commercially available iron(III) tetraphenylporphyrin chloride (FeIIITPP·Cl) catalyst via a synergetic effect with the imidazolium dications of the ionic liquid electrolyte. This procedure enhanced the performance of catalytic systems in the electrochemical production of CO and enabled us to perform different tandem CO2 reduction-carbonylation reactions under mild conditions.

Reverse Semi-Combustion Driven by Titanium Dioxide-Ionic Liquid Hybrid Photocatalyst.

Unprecedented metal-free photocatalytic CO2 conversion to CO (up to 228±48 µmol g-1 h-1) was displayed by TiO2@IL hybrid photocatalysts prepared by simple impregnation of commercially available P25-titanium dioxide with imidazolium-based ionic liquids (ILs). The high activity of TiO2@IL hybrid photocatalysts was mainly associated to (i) TiO2@IL red shift compared to the pure TiO2 absorption, and thus a modification of the TiO2 surface electronic structure; (ii) TiO2 with IL bearing imidazolate anions lowered the CO2 activation energy barrier. The reaction mechanism was postulated to occur via CO2 photoreduction to formate species by the imidazole/imidazole radical redox pair, yielding CO and water.

Diphosphite ligands derived from carbohydrates as stabilizers for ruthenium nanoparticles: promising catalytic systems in arene hydrogenation.

Ruthenium nanoparticles (RuNPs) were prepared through the hydrogenation of [Ru(COD)(COT)] (COD = 1,5-cyclooctadiene, COT = 1,3,5-cyclooctatriene) in the presence of diphosphites derived from carbohydrates as stabilizing agents, and interestingly, structural modifications of the diphosphite backbone were found to influence nanoparticle size and dispersity, as well as their catalytic activity in arene hydrogenation.

Facile synthesis of NHC-stabilized Ni nanoparticles and their catalytic application in the Z-selective hydrogenation of alkynes.

Well defined Ni nanoparticles (NiNPs) stabilized with N-heterocyclic carbenes (NHCs) have been synthesized through a new methodology involving the decarboxylation of a zwitterionic CO2 adduct. Their catalytic performance was tested in the partial hydrogenation of alkynes into (Z)-alkenes under very mild reaction conditions (50 °C and 5 bar H2 pressure), providing excellent activities and selectivities.

Carbon Dioxide Transformation in Imidazolium Salts: Hydroaminomethylation Catalyzed by Ru-Complexes.

The catalytic species generated by dissolving Ru3 (CO)12 in the ionic liquids 1-n-butyl-3-methyl-imidazolium chloride or 1-n-butyl-2,3-dimethyl-imidazolium chloride are efficient multifunctional catalysts for: (a) reverse water-gas shift, (b) hydroformylation of alkenes, and (c) reductive amination of aldehydes. Thus the reaction of alkenes with primary or secondary amines (alkene/amine, 1:1) under CO2 /H2 (1:1) affords the hydroaminomethylations products in high alkene conversions (up to 99 %) and selectivities (up to 96 %). The reaction proceeds under relatively mild reaction conditions (120 °C, 60 bar=6 MPa) and affords selectively secondary and tertiary amines. The presence of amine strongly reduces the alkene hydrogenation competitive pathway usually observed in the hydroformylation of terminal alkenes by Ru complexes. The catalytic system is also highly active for the reductive amination of aldehydes and ketones yielding amines in high yields (>90 %).