Simona Coman

Efficient bio-conversion of glycerol to glycerol carbonate catalyzed by lipase extracted from Aspergillus niger

A biocatalytic synthesis of glycerol carbonate (GlyC), as an added-value product of renewable glycerol, has been developed using a catalytic route in which glycerol (Gly) was reacting with dimethyl carbonate (DMC) in the presence of lipase under solvent-free conditions. The enzyme screening indicated lipase from Aspergillus niger as the most efficient biocatalyst for the GlyC synthesis. After the optimization of the reaction conditions it was established that the best results corresponded to 12% (w/w) Aspergillus nigerlipase, to a glycerolu2006:u2006DMC molar ratio of 1u2006:u200610, to an incubation time of 4 h and to an incubation temperature of 60 °C. Consequently, the glycerol conversion was around 74%, the yield in GlyC of 59.3% and the selectivity to GlyC of 80.3%. Recycling experiments demonstrated that the biocatalyst can be successfully used for several reaction cycles (at least 4 times) and confirmed its very high stability under the reaction conditions.

Strategy of cross-linked enzyme aggregates onto magnetic particles adapted to the green design of biocatalytic synthesis of glycerol carbonate

A new strategy for the preparation of biocatalysts based on enzyme immobilization was explored, leading to cross-linked enzyme aggregate onto magnetic particles (CLEMPA). Lipase enzyme from Aspergillus niger was precipitated from aqueous solution followed by cross-linking of the enzyme aggregates onto magnetic particles using glutaraldehyde as cross-linker. An optimization study has been carried out for the CLEMPA approach to determine the best experimental conditions for both preparation steps (i.e. enzyme precipitation and cross-linking of the enzyme aggregates onto magnetic particles). Type and concentration of the precipitation agent, type and size of magnetic particles, ratio of lipase to magnetic particles, concentration of the cross-linker and growth time of CLEMPA clusters were the experimental factors taken under investigation. Characterization of CLEMPA biocatalyst considering the cluster size and lipase loading was performed using light scattering detection and UV-vis spectrophotometric techniques. The catalytic capacity of CLEMPA biocatalyst was tested with the “green” alternative of glycerol carbonate (GlyC) synthesis. CLEMPA catalyzed the conversion of glycerol to GlyC with an excess of dimethyl carbonate (DMC) providing solvent-free conditions for the reaction. These experiments resulted in encouraging biocatalytic performance with 61% glycerol conversion, 55% GlyC yield and 90% selectivity in GlyC. CLEMPA biocatalyst was also tested in the reaction of “crude” glycerol extracted from the biodiesel process, with similar performance results. Recycling experiments for 20 successive reaction cycles demonstrated the robustness of the prepared CLEMPA structure.

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 (20u2005nm lateral size, 3-4u2005nm 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.

Biocatalytic designs for the conversion of renewable glycerol into glycerol carbonate as a value-added product

A comparative study of two different biocatalytic models, e.g. enzyme immobilized on magnetic particles (EIMP) and cross-linking enzyme aggregates onto magnetic particles (CLEMPA) was performed. The first model was designed as enzyme-immobilized on the magnetic particles surface (EIMP). The second model was constructed as a network structure with the enzyme aggregates and magnetic particles placed into the nodes and polyglutaraldehyde cross-linker as the network ledges. The design was called cross-linking enzyme aggregates onto magnetic particles (CLEMPA). The biocatalysts were prepared using lipase enzyme from Aspergillus niger for catalyzing the glycerol (Gly) conversion to glycerol carbonate (GlyC). The biocatalyst characteristics for both designs (EIMP and CLEMPA) were evaluated using scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis techniques. The EIMP model was strongly influenced by the composition of the polymeric layer covering the particles surface, while the size of the magnetic particles affected mostly the CLEMPA design. Also, the biocatalytic capacity of the tested models was evaluated as maximum 52% Gly conversion with 90% GlyC selectivity for EIMP, and 73% Gly conversion with 77% GlyC selectivity for CLEMPA. Both biocatalytic models were successfully used to prepare GlyC from “crude” glycerol collected directly from the biodiesel process (e.g. 49% Gly conversion with 91% GlyC selectivity for EIMP and 70% Gly conversion with 80% GlyC selectivity for CLEMPA).

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.

Nanoscaled Metal Fluorides in Heterogeneous Catalysis

This chapter focuses on nanoscopic metal fluorides and hydroxide fluorides prepared via a recently explored fluorolytic sol–gel synthesis approach. Metal fluoride phases obtained via this route exhibit exciting catalytic properties making them distinctly different as compared with their classically prepared homologues. As a result, very strong solid Lewis acids are available that give access to new catalytic reactions with sometimes unexpectedly high conversion degrees and selectivity. Even more interestingly, metal hydroxide fluorides can be obtained via this synthesis route, being not at all accessible via any other approach. The fluorolytic sol–gel synthesis allows an adjustment of the hydroxide to fluoride ratio over a wide range. Thus, biacidic (Bronsted and Lewis) solids with tunable Lewis to Bronsted acidity are available that show interesting catalytic properties in a variety of different reactions. Finally, these new nanometal fluorides, due to their very high surface areas and distinct acidic properties, are excellent candidates as support for many novel metal-catalyzed reactions, showing surprising synergistic effects. This chapter will briefly outline the synthesis approach of the fluorolytic sol–gel route with some mechanistic aspects, will present characteristic bulk and surface properties, and will give several examples of novel catalytic applications of nanoscaled metal fluorides in purely Lewis acid and in biacidic catalyzed reactions, and will also exemplarily show the potential of these new materials as supports for heterogeneous catalytic reactions.