Natalia Candu

High catalytic activity of oriented 2.0.0 copper(I) oxide grown on graphene film

Metal oxide nanoparticles supported on graphene exhibit high catalytic activity for oxidation, reduction and coupling reactions. Here we show that pyrolysis at 900 °C under inert atmosphere of copper(II) nitrate embedded in chitosan films affords 1.1.1 facet-oriented copper nanoplatelets supported on few-layered graphene. Oriented (1.1.1) copper nanoplatelets on graphene undergo spontaneous oxidation to render oriented (2.0.0) copper(I) oxide nanoplatelets on few-layered graphene. These films containing oriented copper(I) oxide exhibit as catalyst turnover numbers that can be three orders of magnitude higher for the Ullmann-type coupling, dehydrogenative coupling of dimethylphenylsilane with n-butanol and C–N cross-coupling than those of analogous unoriented graphene-supported copper(I) oxide nanoplatelets.

One‐Step Pyrolysis Preparation of 1.1.1 Oriented Gold Nanoplatelets Supported on Graphene and Six Orders of Magnitude Enhancement of the Resulting Catalytic Activity

Pyrolysis of chitosan films containing Au(3+) renders 1.1.1 oriented Au nanoplatelets (20 nm lateral size, 3-4 nm height) on a few layers of N-doped graphene (Au/fl-G), while the lateral sides were 0.0.1 oriented. Comparison of the catalytic activity of Au/fl-G films with powders of unoriented Au NPs supported on graphene showed that Au/fl-G films exhibit six orders of magnitude enhancement for three gold-catalyzed reactions, namely, Ullmann-like homocoupling, C-N cross coupling, and the oxidative coupling of benzene to benzoic acid. This enhancement is the result of the defined morphology, facet orientation of Au nanocrystals, and strong gold-graphene interaction.

Efficient magnetic and recyclable SBILC (supported basic ionic liquid catalyst)-based heterogeneous organocatalysts for the asymmetric epoxidation of trans-methylcinnamate

A green alternative, based on the use of an efficient and recyclable chiral ketone@SBILC@MWCNT@Fe3O4 catalytic system (Y = 35%, S = 100% and ee = 100%), was developed for the asymmetric epoxidation of trans-methylcinnamate to (2R,3S)-phenyl glycidate.

Replacing benzyl chloride with benzyl alcohol in heterogeneous catalytic benzylation of aromatic compounds

Comparative catalytic liquid-phase benzylation of aromatic compouds (e.g., benzene and ethylbenzene) to diphenylmethane (DPM) derivatives with benzyl alcohol (BnOH) was investigated over various catalysts like zeolite (HSZ 600 mordenite, CBV 20A mordenite, H-beta zeolites with Si/Al ratios of 10.8 and 35.8, respectively) and nano-structured inorganic fluorides (MgF2) at 80–120 °C under atmospheric pressure. The reactions were carried out in batch reactors using two methodologies: (i) by introducing both the solution of substrate and BnOH at the beginning of the reaction, and (ii) by drop-wise addition of BnOH (1–2 drops/min for 4 h) to the reaction mixture. The analysis of the reaction products indicated that the conversion and product distribution depend on the experimental method and the nature of the catalyst. The reaction rate was found to correlate to the nucleophilicity of the substrates and their ability to delocalize the positive charge in the Wheland intermediate by inductive and resonance effects.

Nb-Based Zeolites: Efficient bi-Functional Catalysts for the One-Pot Synthesis of Succinic Acid from Glucose

The one-pot production of succinic acid from glucose was investigated in pure hot water as solvent using Nb (0.02 and 0.05 moles%)-Beta zeolites obtained by a post-synthesis methodology. Structurally, they are comprised of residual framework Al-acid sites, extra-framework isolated Nb (V) and Nb2O5 pore-encapsulated clusters. The Nb-modified Beta-zeolites acted as bi-functional catalysts in which glucose is dehydrated to levulinic acid (LA) which, further, suffers an oxidation process to succinic acid (SA). After the optimization of the reaction conditions, that is, at 180 °C, 18 bar O2, and 12 h reaction time, the oxidation of glucose occurred with a selectivity to succinic acid as high as 84% for a total conversion.

Direct conversion of cellulose to α-hydroxy acids (AHAs) over Nb2O5-SiO2-coated magnetic nanoparticles

Abstract A series of Nb (3 wt% or 60 wt% Nb2O5)-based magnetic nanocomposites (Nb-Si@MNP) was prepared by covering the magnetic cores with Nb2O5-SiO2 shells using either co-precipitation or sol-gel followed by precipitation methods. These materials were exhaustively characterized through XRD, Raman spectroscopy, CO2- and NH3-TPD, DRIFT spectroscopy, and TG-DTA, after which the catalytic one-pot conversion of cellulose to valuable α-hydroxy-acids (i.e. lactic and glycolic acids) was investigated. The catalytic performances, expressed in terms of lactic and glycolic acid yields, were directly correlated to the nature of the catalytic sites which, in turn, depended on the niobia content and the preparation route.

A new chiral dimanganese(III) complex: synthesis, crystal structure, spectroscopic, magnetic, and catalytic properties

Two enantiomeric complexes of formula [MnIII2(μ-OCH3)2(R-valBINAM)2]·1.75DMF (1) and [MnIII2(μ-OCH3)2(S-valBINAM)2]·2DMF (2) [valBINAM = 1,1′-binaphthalene-2,2′-bis(3-methoxysalicylideneiminate)] have been synthesized using as a ligand the chiral Schiff bases resulting from the condensation reactions between o-vanillin and the chiral 1,1′-binaphthyl-2,2′-diamine. The structures of 1 and 2 which have been solved by single crystal X-ray diffraction consist of neutral dimers, the manganese(III) ions being bridged by two methoxido anions, arising from the solvent, and by two valBINAM2− ligands. Their circular dichroism spectra at room temperature emphasize the occurrence of the exciton coupling effect. The cryomagnetic measurements in the temperature range 2.0–300, for compound 2, reveal the occurrence of antiferromagnetic interactions between the two MnIII ions (J = −35.5 cm−1, the Hamiltonian being defined as H = −JS1S2). The catalytic behaviour of these complexes was checked in the epoxidation of methyl trans-cinnamate with N-methylmorpholine-N-oxide as an oxidant. The influence of the solvent was also investigated. The reactions in a CH3CN/H2O (5:1 v/v) solvent mixture afforded total chemo- and enantioselectivity in the desired epoxides.