Carboxymethyl ß-Cyclodextrin Assistance for the 4-Nitrophenol Reduction Using Cobalt-Based Layered Double Hydroxides.

Cobalt-aluminum-layered double hydroxides containing carboxymethyl ß-cyclodextrin (CMßCD) were synthesized by coprecipitation and evaluated as a cobalt source for the 4-nitrophenol reduction in an aqueous medium. Several physicochemical techniques (XRD, FTIR, TGA) indicated the intercalation of the anionic cyclodextrin without damages to the hydrotalcite-type structure. These lamellar cobalt-aluminum hybrid materials (CoAl_CMßCD) were evaluated in the 4-nitrophenol reduction and showed higher activities in comparison with the CMßCD-free standard material (CoAl_CO3). To rationalize these results, a set of experimental controls going from physical mixtures of CoAl_CO3 with different cyclodextrins to other cobalt-based materials were investigated, highlighting the beneficial effects of both the layered double hydroxide and CMßCD-based hybrid structures. CMßCD also showed a beneficial effect as an additive during the 4-nitrophenol reduction. CoAl_CO3, dispersed in a fresh CMßCD solution could be re-used for five successive cycles without the loss of activity.

Robust Ruthenium Catalysts Supported on Mesoporous Cyclodextrin-Templated TiO2-SiO2 Mixed Oxides for the Hydrogenation of Levulinic Acid to γ-Valerolactone.

In this paper, we present a versatile template-directed colloidal self-assembly method for the fabrication in aqueous phase of composition-tuned mesoporous RuO2@TiO2-SiO2 catalysts. Randomly methylated ß-cyclodextrin/Pluronic F127 supramolecular assemblies were used as soft templates, TiO2 colloids as building blocks, and tetraethyl orthosilicate as a silica source. Catalysts were characterized at different stages of their synthesis using dynamic light scattering, N2-adsorption analysis, powder X-ray diffraction, temperature programmed reduction, high-resolution transmission electron microscopy, high-angle annular bright-field and dark-field scanning transmission electron microscopy, together with EDS elemental mapping. Results revealed that both the supramolecular template and the silica loading had a strong impact on the pore characteristics and crystalline structure of the mixed oxides, as well as on the morphology of the RuO2 nanocrystals. Their catalytic performance was then evaluated in the aqueous phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) under mild conditions (50 °C, 50 bar H2). Results showed that the cyclodextrin-derived catalyst displayed almost quantitative LA conversion and 99% GVL yield in less than one hour. Moreover, this catalyst could be reused at least five times without loss of activity. This work offers an effective approach to the utilization of cyclodextrins for engineering the surface morphology of Ru nanocrystals and pore characteristics of TiO2-based materials for catalytic applications in hydrogenation reactions.

Synthesis of novel catalytic composite nanofibers containing ruthenium nanoparticles stabilized by a citric acid-ß-cyclodextrin polymer.

The elaboration of catalytic composite nanofibers (NFs) by electrospinning through a one-pot strategy is described. First, aqueous colloidal suspensions of ruthenium nanoparticles (Ru NPs) formed by reduction of a Ru(iii) salt with NaBH4 and stabilized by poly(cyclodextrin citrate) (PCD) were prepared. Then, poly(vinyl alcohol) (PVA) of different molecular weights was dissolved in the colloidal suspensions that were electrospun. SEM analyses of the resulting nanowebs displayed uniform NFs, whose diameters ranged between 300 and 700 nm and enlarged upon increasing (i) PVA molecular weight, (ii) nanosuspension viscosity, (iii) the amount of NaBH4 and (iv) the PCD/Ru NP concentration. TEM analysis confirmed that Ru NPs with a mean diameter of around 2 nm were observed at the surface of NFs, embedded in the PVA matrix of NFs. HAADF-STEM and EDS mapping clearly showed that Ru NPs were homogeneously distributed onto and into the matrix of NFs. After their electrospinning, the prepared nanowebs were submitted to a heat post-treatment at 160 °C which was shown to trigger the PVA crystallization. In addition, the physical crosslinking of PVA chains by NaBO2 resulting from NaBH4 oxidation in the precursor suspension was also observed. Interestingly, an SEM study evidenced that the thermal post-treatment in combination with the presence of NaBO2 clearly improved the thermal stability of the synthesized composite nanowebs. Finally, catalytic hydrogenation tests showed the absence of Ru NPs leaching from NFs in the reaction medium, and displayed good conversion of styrene into ethylbenzene.

Carboxylated polymers functionalized by cyclodextrins for the stabilization of highly efficient rhodium(0) nanoparticles in aqueous phase catalytic hydrogenation.

Rhodium(0) nanoparticles stabilized by a polymer containing carboxylate and ß-cyclodextrin moieties have high stability and catalytic activity for aqueous hydrogenation reactions of olefins and aromatic substrates. This catalytic system can be recycled and reused without loss of activity. These high catalytic performances can be attributed to conjugated electrostatic interactions (carboxylate groups) and steric interactions (polymer structure and ß-cyclodextrin moiety).

Cyclodextrins as growth controlling agents for enhancing the catalytic activity of PVP-stabilized Ru(0) nanoparticles.

Cyclodextrins act as growth controllers in the synthesis of PVP-stabilized Ru(0) nanoparticles, leading to enhancement of the catalytic activity in the hydrogenation of furfural.

Direct synthesis of tricyclic 5H-pyrido[3,2,1-ij]quinolin-3-one by domino palladium catalyzed reaction.

Unexpectedly, the palladium catalyzed coupling reaction of acrolein with 8-bromoquinoline gave 5H-pyrido[3,2,1-ij]quinolin-3-one in a single step.