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  • Open access
  • 85 Reads
Microwave-Assisted Continuous Flow for the Selective Oligomerization of Glycerol

Considering the programmed decrease in oil resources, the concept of biorefinery is in the spotlight of the chemical industry [1-5]. In particular, the use of vegetable oils is a promising alternative to meet future challenges [6-8]. Among the oilseed chemicals, glycerol is an outstanding example with great potential for conversion into valuable products. Glycerol, propan-1,2,3-triol, is a symmetrical polyol with three hydroxy (OH) groups: two identical primary OHs and a secondary OH with a similar pKa and therefore close reactivity. Several chemical modifications obtained by oxidation, hydrogenolysis, etherification, esterification, dehydration and oligomerisation of glycerol have led to the production of a large number of value-added chemicals with specific applications in the polymer, agrochemical and pharmaceutical industries. The continuous oligomerisation of glycerol for the production of polyglycerol was carried out for the first time under microwave activation. In the presence of potassium carbonate, a homogeneous commercial catalyst, different parameters: temperature, flow rate and residence time were studied. The main linear and branched-chain diglycerol and triglycerol regioisomers were characterised and the distribution of the different oligomers was quantified. Further investigations in cyclic mode, combined with short distance distillation, allowed the mixture to be enriched with glycerol digesters and thus to obtain the following mixture: glycerol dimer (50.2 % by weight), glycerol trimer (22.1 wt%), glycerol tetramer (9.5 wt%) and glycerol pentamer (4.3 wt%).

  • Open access
  • 69 Reads
Electrocatalysis of Ethanol and Methanol Electrooxidation by Composite Electrodes with NiOOH/FeOOH Supported on Reduced Graphene Oxide onto Composite Electrodes

In this work, graphite/paraffin composite electrodes with microparticles nickel (Ni) and Ni-Fe alloy anchored in reduced graphene oxide (RGO) were confection by the electrosynthesis of the microparticles at reduction potentials from -0.7V to -1.2V (v= 50 mV/s) onto RGO nanosheets, reduced by cyclic voltammetry from a solution of 1 mg/mL of GO in PBS solution with pH 9.18, in potential range from -1.5V to 0.5V (v= 10 mV/s). After electrodeposition of metals, oxyhydroxides were formed by cyclic voltammetry in an alkaline medium of 0.1 mol/L of NaOH in a potential range of -0.2V to 1.0V (v= 100 mV/s) with successive scans until stabilization of currents. The composites were investigated by scanning electron microscopy (SEM), it was observed that the Ni microparticles had spherical shapes, while the Ni-Fe alloy did not present a defined shape. In order to evaluate the electrochemical performance of the developed composite electrodes, ethanol and methanol electrooxidation was carried out in an alkaline medium of 0.1 mol/L of NaOH in a potential range of -0.2V to 1.0V (v= 50 mV/s) by cyclic voltammetry and chronoamperometry. The electrodes were able to induce the electrooxidation of ethanol at a potential of around 0.55V for the electrode constituted by the Ni-Fe alloy and around 0.6V for the electrode modified with Ni, and for methanol in a potential around 0.55V for the Ni-Fe alloy and around 0.65V for the Ni electrode. The Ni-Fe alloy electrodes showed the electrocatalysis of the alcohols in relation to Ni electrodes.

  • Open access
  • 52 Reads
Selection of the Optimal Medium for Adsorption of Plant Protease

Immobilized enzymes are the most sought preparations on the world market. They are used in medicine, veterinary food industry, winemaking and brewing. The simplest method for immobilizing biocatalysts on insoluble carriers is the adsorption. Its advantage is to preserve the natural conformation of the enzyme, which slightly reduces its catalytic ability compared to the native form. Ficin (EC, papain (EC, bromelain (EC (Sigma) were chosen as objects of study, azocasein (Sigma) was used as a substrate for hydrolysis, and an acid-soluble high molecular weight chitosan (350 kDa, Bioprogress CJSC) was used as an immobilization carrier. Suitable buffer systems for immobilization were identified by the optimal ratio of protein content (mg per g of carrier), total activity (in units per ml of solution) and specific activity (in units per mg of protein). Ficin is immobilized on a chitosan matrix using glycine buffer with pH of 8.6. Glycine buffer with pH of 8.6-10.5 is optimal medium for adsorption of papain on chitosan. Bromelain is immobilized on a chitosan matrix under Tris-glycine buffer with pH 8.5 conditions.

This work was financially supported in the form of a grant from the President of the Russian Federation for state support to young Russian scientists - doctors of sciences (MD-1982.2020.4. Agreement 075-15-2020-325).

  • Open access
  • 139 Reads
Photochemical Treatment of Blue-Indigo using TiO2-Sunligth System in Heterogeneous Conditions.

Abstract: Ecuador is one of the countries in the Latin American region with high textile production. However, chemical treatment strategies in the Ambato, Tungurahua and Quito areas are inefficient and not systematically applied, and the volumes of dyes and pigment-type contaminants generate serious environmental problems. The treatments of indigo textile wastewater and related indigo derivatives are very complex. Taking theses into consideration, was developed a simple photochemical protocol, in heterogeneous conditions, for degrading “blue-indigo” (Ambato textile group) in solution, using TiO2 (Degussa P25, with purity of ≈ 99 % and BET surface area 50 ± 15 m2/g) and solar light at lab scale. The photocatalytic oxidation of organic dye“blue indigo” in aqueous solution was assessed by solar irradiation, in the presence of TiO2 particles. The effect of indigo concentrations, pH and TiO2 loading for maximum degree of degradation were evaluated. The mineralization of “blue indigo” was reported by measuring COD-i and COD-f of the solution that was irradiated with sun light (60-100 minutes) under optimized conditions. Taking into consideration the results was proposed a probable mechanism of degradation .The results allows to re-design, in eco-sustainable conditions, for Ecuador, the strategies for controlling contamination in textile wastewaters.

  • Open access
  • 66 Reads
Covalent Immobilization of Thiol Proteases on Chitosan

Plant enzymes such as ficin (EC, papain (EC and bromelain (EC are obtained from tropical plants. These biocatalysts belong to thiol proteases, in the active center of which cysteine is contained. Ficin, papain and bromelain have a wide substrate specificity, which provides a demand for their use in various industries. Enzymes in the free state are less commonly used; immobilized biocatalysts are the preferred form. The aim of this work was to determine the optimal concentration of a crosslinking agent in the covalent immobilization of ficin, papain and bromelain on a chitosan matrix. Ficin, papain, bromelain (Sigma) were chosen as objects of study. An acid-soluble chitosan (350 kDa, Bioprogress CJSC) was used as an immobilization carrier. The concentration range of glutaraldehyde (crosslinking agent) ranged from 1 to 25%. Suitable concentration of glutaraldehyde for covalent immobilization were identified by the optimal ratio of protein content (mg per g of carrier), total activity (in units per ml of solution) and specific activity (in units per mg of protein). It was shown that for covalent immobilization of ficin and bromelain on a chitosan matrix, it is most promising to use 10 % glutaraldehyde. For immobilization of papain on chitosan by covalent means, the concentration of glutaraldehyde equal to 20 % is optimal.

This work was financially supported in the form of a grant from the President of the Russian Federation for state support to young Russian scientists - doctors of sciences (MD-1982.2020.4. Agreement 075-15-2020-325).

  • Open access
  • 196 Reads
Fenton Degradation of Ofloxacin using a Montmorillonite-Fe3O4 Composite

In this work, FeM composites consisting of montmorillonite and variable amounts of Fe3O4 were successfully synthesized via a facile co-precipitation process. They were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), N2 adsorption-desorption and Fourier transform infrared spectroscopy (FT-IR) techniques to explain the effect of Fe3O4 content on the physicochemical properties of the Fe3O4-montmorillonite (FeM) composites. The FeM composites were subsequently used as heterogeneous Fenton catalysts to activate green oxidant (H2O2) for the subsequent degradation of ofloxacin (OFL) antibiotic. The efficiency of the FeM composites was studied by varying various parameters of Fe3O4 loading on montmorillonite, catalyst dosage, initial solution pH, initial OFL concentration, different oxidants, H2O2 dosage, reaction temperature, inorganic salts and solar irradiation. Under the conditions of 0.75 g/L FeM-10, 5 mL/L H2O2, and natural pH, almost 81 % of 50 mg/L of OFL was degraded within 120 min in the dark, while total organic carbon (TOC) reduction was about 56 %. Moreover, the FeM-10 composite maintained high efficiency and was stable even after four continuous cycles, making it a promising candidate in real wastewater remediation. Results from such study have confirmed that synergetic effect between Fe3O4- montmorillonite and H2O2 is necessary, in order to achieve higher efficiency.

  • Open access
  • 108 Reads
Synthesis and Characterization of Pd over Novel TiO2 Mixtures: Insights on Metal-Support Interactions
, , , ,

Palladium nanoparticles were supported on unusual mixtures of anatase, TiO2 (II) and rutile titania phases (not commercially available) by wet impregnation, obtaining catalysts with metal contents of 0.25 wt% labeled Pd/Ti5, Pd/Ti45 and Pd/Ti120. Crystalline structures were confirmed by X-Ray Diffraction (XRD) and Raman Spectroscopy. Pd loadings were quantified by Inductively Coupled Plasma (ICP-OES) whilst particle sizes in the range 4-20 nm were obtained by Transmission Electron Microscopy (TEM). Low-values of external surface area (SBET) in the range 10-17 m2 g-1, measured by Brunauer-Emmet-Teller (BET) method, were higher enough to achieve a good distribution of palladium over titanium oxide outer surface, as evidenced by Energy-Dispersive X-ray Spectroscopy (EDS) elemental mapping. Pd0/Pdδ+ atomic ratio measured by X-Ray Photoelectron Spectroscopy (XPS) showed a decrease from Pd/Ti5 to Pd/Ti120, in line with the decrease in anatase phase present in the catalysts. This behavior suggested that palladium tended to form more TiPdxO structures in Pd/Ti5 whilst PdOx structures were more likely to be present on supports with greater amounts of TiO2 (II) and rutile phases, due to the distinct metal-support interactions. An increase in reducibility and oxygen mobility from Pd/Ti5 to Pd/Ti120 was observed by Temperature Programmed Measurements (TPM), which could be associated to the different defective structures achieved in the supports previously synthesized by high-energy ball milling. Catalysts with improved properties reported herein could exhibit an excellent performance in oxidation reactions, e.g. liquid-phase glycerol selective oxidation.

  • Open access
  • 65 Reads
Highly Active Pandanus Nanocellulose-Supported Poly(amidoxime) Copper (II) Complex for Ullmann Cross-Coupling Reaction

The transition metal-catalyzed chemical transformation of organic electrophiles, and organometallic reagents have turned up as an exceedingly robust synthetic tool. The evolution of transition metal catalysts has attained a stage of civilization that authorizes for an extensive scope of chemical bonds formation partners to be combined efficiently. The applications of Cu-based nanoparticles have received great attention owing to the earth-abundant, low toxicity and inexpensive. Due to these characteristics, copper nanoparticles have generated a great deal of interest especially in the field of catalysis. In this study, bio-waste pandanus fiber nanocellulose-graft-poly(acrylonitrile) was synthesized by undergoes free-radical initiation process and followed by Beckmann-type rearrangement with hydroxylamine under alkaline conditions converted into the poly(amidoxime) ligand and anchored the copper onto poly(amidoxime) functionalized pandanus nanocellulose. Biocatalyst; CuNPs@ PAM was characterized using different techniques such as FTIR, FE-SEM, EDX, TEM, TGA, DSC, ICP-OES, XRD and XPS analyses. The CuNPs@ PAM showed high stability and high catalytic activity in a wide variety of electrophilic substituted phenols with substituted aryl/benzyl halides. 0.03 mol%, ±3 mg of CuNPs@ PAM could efficiently promoted Ullmann reaction to give the corresponding coupling product in up to 99 % yields. The complex was easy separated and recover from the reaction mixture by simple filtration. Leaching studies performed by hot filtration experiments show that the synthesize copper catalyst are stable under the reaction conditions

  • Open access
  • 182 Reads
Combined DFT and operando Spectroscopic Study of the Water-Gas Shift Reaction over Ceria based Catalysts: The Role of the Noble Metal and Ceria Faceting

In the low-temperature (>200°C) water-gas shift reaction (LT-WGS) supported metals like gold or copper on active supports such as ceria have been proven to be good alternatives to the conventional copper-zinc oxide catalysts used in industry. According to the current state of research, the role of the metal itself and of the ceria faceting during reaction are considered. Therefore, in this study supported copper or gold on different ceria facets will be investigated by operando Raman and UV/Vis spectroscopy during LT-WGS conditions. In this context the different properties of the metal itself have influence on the activity, in which the copper-loaded catalysts generally show lower activities than the gold loaded ones. Looking at the reducibility, probed by the F2g shift using Raman spectroscopy, both supported metals improve the reducibility of the support, but comparing between copper and gold there are no major differences in reducibility. Furthermore, it is shown that the ceria facet has strong influence on the activity, whereby supported CeO2(111) shows the highest activity. Therefore, it is not only the reducibility of the support that is responsible for the high activity and thus other factors like interactions of the ceria facet with the metal or the coordination role of the metal for intermediates are important, which can be investigated more precisely by DFT calculations.

Summarizing, our results demonstrate the potential of the operando spectroscopies combined with DFT calculations to elucidate the metal and facet related dynamics at metal-supported catalysts during LT-WGS conditions.

  • Open access
  • 126 Reads
Comparative Catalytic and Photocatalytic Reduction of NO3- by the in Situ Generated Solar H2 over Pt-Cu/TiO2 Catalysts
Published: 09 November 2020 by MDPI in The 1st International Electronic Conference on Catalysis Sciences session Posters

Studies on the nitrate reduction reaction have shown that the bimetallic catalysts may be more efficient compared to the monometallic ones. To reduce nitrate, it is necessary to activate the precious metal by addition of a promoting second metal. Some studies have pointed out the relevance of the structure and geometry of the metal particles in the final mechanism of nitrate reduction. Well-defined nanoparticles could be used to catalyze structure-sensitive reactions with practical importance (pollution control).

Our investigation aimed to make deeper insight into NO3- catalytic reduction and photocatalytic reduction mechanisms. Two types of Pt-Cu supported on TiO2 materials were employed in order to study the nitrate removal from aqueous phase and the ability of obtaining and using the in situ generated solar H2 as reducing agent. The prepared catalysts were characterized and tested in photocatalytic/catalytic reduction of nitrate in aqueous solution in water splitting reaction. A correlation between the catalytic/photocatalytic performances of the supported Pt-Cu catalysts and their associated physicochemical and adsorption properties has been made. The catalysts activity for the nitrate reduction can be directly related to the interactions between platinum and copper. Deposition with Pt nanoparticles was found to contribute to enhance the photocatalytic activity toward H2 production from aqueous solution. Our future research aims at optimizing the photocatalytic system having as future possible applications for hydrogen production using sunlight and water as the hydrogen source.