An Efficient Strategy to Drive Nanoparticles into Carbon Nanotubes and the Remarkable Effect of Confinement on Their Catalytic Performance

Are you in? Bimetallic PtRu nanoparticles have been selectively confined inside or deposited outside carbon nanotubes (see picture). The confined nanoparticles display significantly higher selectivity and catalytic activity in hydrogenation reactions.

     

Hydrogenation of N‐Acylcarbamates and N‐Acylsulfonamides Catalyzed by a Bifunctional [Cp*Ru(PN)] Complex

Awakening of the Cp one : The bifunctional complex 1 facilitates the interaction with substrates bearing less electrophilic carbon atoms than ketones, epoxides, and imides. The title reaction was applicable to the reduction of Evans' asymmetric alkylation products to the chiral alcohols along with good recovery of the chiral oxazolidinone auxiliary. EWG=electron‐withdrawing group.

     

Spiro[4,4]‐1,6‐nonadiene‐Based Phosphine–Oxazoline Ligands for Iridium‐Catalyzed Enantioselective Hydrogenation of Ketimines

From imines to amines through catalysis by Ir^I complexes of a new type of P,N ligand (see scheme): This reaction affords the corresponding optically active amines with up to 98 % ee and has also been used with perfect stereoselectivity in the asymmetric synthesis of sertraline ( 1 ), an important antidepressant chiral drug.

     

Multi-Walled Carbon Nanotubes as a Novel Promoter of Catalysts for CO/CO2 Hydrogenation to Alcohols

Multi-walled carbon-nanotubes (MWCNTs) are drawing increasing attention in recent years. This material possesses a series of unique features, such as its nanometer-sized channel, highly conductive graphitized tube-wall, sp ²-C-constructed surface, and excellent performance for adsorption and spillover of hydrogen, which make the MWCNTs full of promise to be a novel catalyst support or promoter. This article will review the recent progress in applied research of MWCNTs as a novel promoter in heterogeneous catalysis for active components, including metals and their oxides, with the emphasis on the study and development of MWCNT-promoted catalysts related to CO/CO₂ hydrogenation to alcohols and dimethyl ether based on the recent works carried out in our laboratory.     

Nanostructured Macromolecular Metal Containing Materials in Catalysis

Summary: Nanostructured regular materials based on cross-linked polypropylene imine (PPI) dendrimers and silica-gel polyamine composites were used as a support for the synthesis of Pd nanoparticles. The materials were tested as catalysts and displayed a high activity and selectivity for the hydrogenation of conjugated double bonds.     

Highly efficient chiral PNNP ligand for asymmetric transfer hydrogenation of aromatic ketones in water

Chiral PNNP ligand II and [IrHCl₂(COD)]₂ were applied for the first time in the asymmetric transfer hydrogenation of aromatic ketones with HCOONa in water, giving the corresponding optical alcohols in high yield and excellent enantioselectivity (up to 99% ee). Particularly, the reduction of propiophenone proceeded smoothly at a substrate to catalyst molar ratio of 8000, without compromising the ee values obtained.     

Synthesis, crystal structure, and catalytic properties of MgCo6Ge6

The ternary compound MgCo6Ge6 represents a novel member of the RM6X6 phases, which contains a graphite-type Ge network, Kagomé nets of Co atoms, and Ge2 dumbbells with an unexpected short Ge-Ge contact in the range of a localized Ge-Ge single bond. The title compound shows a large variety of chemical bonding, which ranges from metallic to multicenter and covalent bonding. The role of polar intermetallic alloys as promising candidates for the application as catalysts for the selective hydrogenation of alpha,beta-unsaturated aldehydes is discussed. MgCo6Ge6 possesses a remarkable activity and selectivity for the hydrogenation of cis/trans-citral to geraniol and nerol.     

Characterization and catalytic-hydrogenation behavior of SiO2-embedded nanoscopic Pd, Au, and Pd-Au alloy colloids

Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au M?ssbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene.