Ferrosilicate-Based Heterogeneous Fenton Catalysts: Influence of Crystallinity, Porosity, and Iron Speciation

Different ferrosilicate samples have been prepared with varying degrees of crystallinity, porous texture, and speciation of the Fe sites by both hydrothermal and sol–gel procedures: Fe-silicalite-1 with microcrystals (2–10 µm) and nanocrystals (180 nm), Fe-containing composite material consisting of silicalite-1 and amorphous silica, and two samples of mesoporous Fe-containing amorphous silica Fe–SiO2. The resulting solids have been tested for their potential as organic pollutants removal under Fenton-like conditions in heterogeneous catalytic wet peroxide oxidation of phenol and clarithromycin lactobionate. Our results indicate that the three aforementioned parameters show a strong interplay towards the abatement of pollutants in liquid phase. Thus, samples with high crystallinity show an improved performance in the oxidation of organic contaminants over amorphous samples in which the Fe speciation is very well controlled.The work was financially supported by the Ministry of Education and Science of the Russian Federation (RFMEFI60417 X 0159, title of the agreement: “Development of methods for hydrotreating of vacuum residue into high-quality marine fuels on macroporous catalysts”). The authors from Spanish side thank the Spanish Ministry of Economy and Competitiveness (MINECO), Generalitat Valenciana and FEDER (CTQ2015-66080-R MINECO/FEDER and PROMETEOII/2014/010) for financial support. J.G.A. thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for his fellowship (BES-2013-063678)

Self-propagating High-temperature Synthesis of Materials Based on Tungsten Carbide for One-Pot Hydrolysis-Hydrogenolysis of Cellulose Into Ethylene Glycol and 1,2-Propylene Glycol

Методом самораспространяющегося высокотемпературного синтеза из смеси оксида вольфрама, металлического магния, технического углерода и CaCO3 с использованием механохимической обработки получены каталитические системы на основе карбида вольфрама (WnC), содержащие преимущественно W2C. Показано, что фазовый состав образующихся материалов зависит от количества CaCO3. Каталитические свойства полученных материалов исследованы в реакции гидролиза-гидрогенолиза целлюлозы до низших полиолов (этиленгликоль (ЭГ) и 1,2-пропиленгликоль (ПГ)). Установлено, что в присутствии WnC основными продуктами реакции являются ЭГ и ПГ с соотношением ПГ/ЭГ – 1,5-1,8. Нанесение наночастиц никеля на поверхность WnC материалов повышает скорость реакции и выход целевых продуктов. Максимальный суммарный выход диолов составил 47,1 мол. %Catalytic systems based on tungsten carbide (WnC) containing mainly W2C were obtained by the method of self-propagating high-temperature synthesis from a mechanochemically activated mixture of tungsten oxide, metallic magnesium, carbon black and CaCO3. The phase composition of the formed materials was shown to depend on the amount of CaCO3. The catalytic properties of the materials were tested in the hydrolysis-hydrogenation of cellulose to ethylene glycol (EG) and 1,2-propylene glycol (PG). It was established that in the presence of WnC the main products of the reaction were EG and PG with a ratio of PG/EG – 1.5-1.8. The deposition of nickel nanoparticles on the WnC surface increased the reaction rate and product yields. The maximum total yield of diols was 47.1 mol. %

Molecular Mechanism of the Formic Acid Decomposition on V₂O₅/TiO₂ Catalysts: A Periodic DFT Analysis

Molecular and dissociative forms of formic acid adsorption on the V₂O₅/TiO₂ model surface, possible intermediates, and transition states along of the dehydrogenation (HCOOH → CO₂ + H₂) and dehydration (HCOOH → CO + H₂O) pathways have been studied by the periodic density functional theory. The CI-NEB analysis of the reaction pathways showed that two types of molecular adsorbed HCOOH species initiate two completely different reaction channels. The first more stable adsorbed form is transformed into the surface formates, which decompose according to the “formate mechanism” to yield products of dehydrogenation, whereas the second weakly adsorbed molecular form decomposes, releasing CO and forming surface hydroxyls. Recombination of two surface hydroxyl groups V–OH to form adsorbed H₂O, followed by water desorption, completes the catalytic dehydration cycle without participation of the formate species. Comparison of the reaction pathways demonstrates that both dehydrogenation and dehydration of formic acid may occur over VO_<i>x</i>/TiO₂ model catalysts with the preferable dehydration pathway

Effect of pH on fluorescence formation related to fish deterioration

5 páginas, 5 tablas.-- The final publication is available at www.springerlink.comEarlier studies have investigated fluorescence at different excitation/emission maxima during common types of fish processing. A shift towards higher wavelength maxima was observed and measured as the ratio between two of the maxima tested. This fluorescence ratio (dF) correlated with increased fish damage. The present work is focused on the effect that pH can have on the formation of fluorescent compounds in fish muscle systems. Minced hake muscle was homogenised with 0.1 M phosphate buffer of different pH values (5, 6, 7 and 8) and was stored at 30 7C for up to 30 days. Lipid damage, measured as the dF value of the aqueous reaction medium and the fish lipid extract, indicated little difference between the effect of different pH values under the conditions employed in the present experiment. The effetct of formaldehyde (FA) in the same reaction medium was also evaluated. It was observed that FA had a positive effect on the fluorescence shift occurring in the aqueous reaction medium, so that a higher dF value was observed for pH 7 and pH 8, especially for the latter. It is concluded that changes in the dF value during fish storage and/or processing are of special interest as, in addition to FA formation and lipid oxidation, significant pH increases are expected to occur as a result of damage.European Community research Project FAIR-CT95-1111.Peer reviewe

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides

Kinetic modeling of the multistep hydrolysis-dehydration of cellulose to platform molecules over a solid carbon acid catalyst in pure water

The present study was devoted to a kinetic modeling of cellulose hydrolysis-dehydration into platform molecules (glucose and 5-hydroxymethylfurfural) over a carbon solid acid catalyst. Cellulose depolymerization and transformations of the main process intermediates were experimentally studied under hydrothermal conditions in pure water over a catalyst based on sulfonated Sibunit material at 180 °C in a batch reactor. Based on the data obtained, the 18-step kinetic scheme of the process which included the main reaction pathways was proposed as well as the reaction constants were determined. Kinetic parameters showed that solid acid carbon catalysts seems to be more suitable than soluble ones for the production of 5-HMF from sugars. Proposed software modeling of cellulose hydrolysis-dehydration described the experimental results obtained with a sufficient accuracy

Heterogeneous Biocatalysts Prepared by Immuring Enzymatic Active Components inside Silica Xerogel and Nanocarbons-In-Silica Composites

Proprietary results on preparation and studies of whole-cell and lysates-based heterogeneous biocatalysts with different enzymatic activity were reviewed. A peculiar method was developed for preparing these biocatalysts by immuring (entrapping) enzymatic active components (EAC) inside silica (SiO2) xerogel and nanocarbons-in-silica composites. Properties of the multi-component composite biocatalysts such as enzymatic activity and operational stability were compared. The effect of the inclusion of nanocarbons such as nanotubes, nanofibers, and onion-like nanospheres with various texture, nanostructure and dispersion were thoroughly studied. With invertase-active biocatalysts, the direct correlation between an increase in the enzymatic activity of the nanocarbons-in-silica biocatalyst and efficiency of EAC adhesion on nanocarbons was observed. The steady-state invertase activity of the baker yeast lysates-based biocatalysts was determined to increase by a factor of 5–6 after inclusion of the multi-walled carbon nanotubes inside SiO2-xerogel. With lipase-active biocatalysts, the effect of the included nanocarbons on the biocatalytic properties depended significantly on the reaction type. In interesterification of oil-fat blends, the biocatalysts without any included nanocarbons demonstrated the maximal lipase activity. In esterification of fatty acids with aliphatic alcohols, the activity of the biocatalysts increased by a factor of 1.5–2 after inclusion of the aggregated multi-walled carbon nanotubes (CNTs) inside SiO2-xerogel. In the low-temperature synthesis of isopentyl esters of butyric (C4:0), capric (C10:0), and srearic (C18:0) fatty acids, the lipase-active composite CNTs-in-silica biocatalysts operated without loss of activity for more than thousand hours