Introduction of Pt and Pd nanoclusters in zeolite cavities by thermal degradation of acetylacetonates

Nanodispersed metallic clusters of platinum and palladium were incorporated into NaX zeolite cavities by impregnation with acetone solution of corresponding acetylacetonates, solvent evaporation and acetylacetonate thermal decomposition. The acetylacetonate decomposition was followed by thermogravimetry. Modified zeolite samples were characterized by x-ray diffractommetry. In order to get a satisfactory electronic conductivity of modified zeolite, 10% wt of carbon black was added. This material was applied to a rotating glassy carbon disc electrode, and was used to study electrochemical water splitting in slightly acidic aqueous solutions. Noble metal modified zeolites exhibit significant reduction in water decomposition overvoltage as compared to smooth polycrystalline platinum

Electrochemical water splitting on zeolite supported platinum clusters

Platinum was incorporated into the cavities of NaX zeolite by impregration/thermal decomposition technique, using Pt(II)-acetylacetonate in acetone as an impregnating solution. The platinum-to-zeolite weight ratio amounted to 0.092. The sample was characterized by thermogravimetry, X-ray diffraction and Na-23 MAS NMR methods. The mixture of modified zeolite and 10 wt. % of carbon black, in a form of thin layer, was pasted to a glassy carbon stance. With such an electrode material, the electrochemical decomposition of aqueous 2.5 mM H2SO4 + 1 M Na2SO4 solution with hydrogen and oxygen production has been kinetically studied. In comparison with smooth polycrystalline platinum, this electrode material provided an remarkable overvoltage drop,for water splitting, primarily due to the acceleration of oxygen evolution reaction

Methanol electrooxidation on PtRu modified zeolite X

Zeolite NaX (faujasite type) was used as a support for platinum-ruthenium catalyst. A procedure for thermal decomposition of noble metal acetylacetonates to deposit noble metal clusters on the surface of solid support was adapted by authors to introduce noble metal clusters in zeolite cavities. The effectiveness of this composite material for methanol electrooxidation from alkaline solution was investigated by cyclic voltammetry. The influence of the concentration of supporting electrolyte, scan rate and rotation rate on the reaction of methanol oxidation was investigated. The obtained activity was compared with literature data for similar catalysts.Zeolit NaX (fožazitnog tipa) korišćen je kao nosač za platina-rutenijumski katalizator. Autori su prilagodili proceduru termalne dekompozicije plemenitih metalnih acetilacetonata kojom su nanošeni klasteri plemenitih metala na površinu čvrste podloge, kako bi se klasteri plemenitih metala su uveli u šupljine zeolita. Efikasnost ovih kompozitnih materijala za reakciju elektrooksidacije metanola je ispitana cikličnom voltametrijom. Ispitan je uticaj koncentracije inertnog (osnovnog) elektrolita, brzine polarizacije i brzine rotacije elektrode na reakciju oksidacije metanola. Dobijena aktivnost je upoređena sa literaturnim podacima za slične katalizatore

Organo-inorganic bentonite for simultaneous adsorption of Acid Orange 10 and lead ions

Partial substitution of the interlayer cations of a local bentonite (Bogovina) by hexadecyl trimethylammonium ions (HDTMA) was performed to prepare adsorbents able to simultaneously adsorb toxic metal cations and organic pollutants. Acid Orange 10 adsorption increased with increasing HDTMA addition, while the adsorption of Pb2+ decreased with increasing organophilicity. The adsorption of the dye and Pb2+ and their mixture onto Na-rich bentonite and HDTMA-bentonites, regardless of adsorbents' organophilicity, obeyed the pseudo-second-order kinetics model. (C) 2009 Elsevier B.V. All rights reserved

Ethylene glycol and glycolic acid production by wild-type Escherichia coli

Ethylene glycol and glycolic acid are bulk chemicals with a broad range of applications. The ethylene glycol and glycolic acid biosynthesis pathways have been produced by microorganisms and used as a biological route for their production. Unlike the methods that use xylose or glucose as carbon sources, xylonic acid was used as a carbon source to produce ethylene glycol and glycolic acid in this study. Amounts of 4.2 g/L of ethylene glycol and 0.7 g/L of glycolic acid were produced by a wild‐type Escherichia coli W3110 within 10 H of cultivation with a substrate conversion ratio of 0.5 mol/mol. Furthermore, E. coli strains that produce solely ethylene glycol or glycolic acid were constructed. 10.3 g/L of glycolic acid was produced by E. coli ΔyqhD+aldA, and the achieved conversion ratio was 0.56 mol/mol. Similarly, the E. coli ΔaldA+yqhD produced 8.0 g/L of ethylene glycol with a conversion ratio of 0.71 mol/mol. Ethylene glycol and glycolic acid production by E. coli on xylonic acid as a carbon source provides new information on the biosynthesis pathway of these products and opens a novel way of biomass utilization

Removal of Tc-99(VII) by organo-modified bentonite

(99)Technetium is one of the largest components of nuclear waste material. In aqueous solutions Tc-99 is present as the pertechnetate oxoanion, (TcO4-)-Tc-99, which is highly soluble and mobile in groundwater under oxidizing conditions, thus posing a major environmental concern. In this study, a series of organo-modified bentonite clay samples was tested as adsorbents for the removal of radioactive (TcO4-)-Tc-99 from aqueous solution at room temperature. The influence of the hexadecyl trimethylammonium (HDTMA)/bentonite ratio on the adsorption ability of the organobentonites was investigated. It was found that the adsorbent in which the exchangeable cations were only partially substituted with HDTMA showed very low affinity toward pertechnetate. On the other hand, the adsorbents in which the HDTMA loading exceeded the cation exchange capacity (CEC) value had high efficiency. The behavior of such adsorbents was best described by a Freundlich isotherm, while for the sample in which the HDTMA loading was equal to the CEC, the linear adsorption isotherm was the most appropriate. The difference in adsorption performance of several adsorbents was discussed from the point of view of the interlayer arrangement of the HDTMA. The kinetics of pertechnetate adsorption on HDTMA-bentonites was tested and analyzed using different surface reaction- and diffusion-based kinetic models. For all the investigated adsorbents, the most appropriate kinetic model was the pseudo-second-order kinetics model. The obtained adsorption capacities were and HDTMA-bentonites with HDTMA loadings exceeding CEC value should be regarded as very promising adsorbents for the remediation of Tc-99 polluted waters. (C) 2014 Elsevier B.V. All rights reserved

Synergic adsorption of Pb2+ and reactive dye-RB5 on two series of organomodified bentonites

Two series of organobentonites (OBs) were synthesized from Na+-exchanged bentonite clay from Bogovina, Serbia. In the first series the starting material was modified using hexadecyltrimethylammonium (HDTMA(+)) ion in the amounts corresponding to 0.2, 0.5, 1.0 and 2.0 of the CEC value. The second series was obtained using quaternary alkyl ammonium cations (QAACs) with different alkyl chain lengths: hexadecyltrimethylammonium (HDTMA(+)), dodecyltrimethylammonium (DDTMA(+)) and tetramethylammonium (TMA(+)) ions. The synthesized OBs were characterized. The adsorption of anionic reactive dye Reactive Black 5 (RB5) and Pb2+ from single component solutions and their hi-component solution was investigated for both series of OBs. The adsorptive properties of the OBs were correlated to the amount and type of incorporated QAACs. The correlation was tested using different mathematical models and best fits were found. Experimental results showed that simultaneous adsorption of RB5 and Pb2+ exhibited synergic effect. The adsorption capacity for both RB5 and Pb2+ was higher in their hi-component solution than in single-component solutions. These results indicate the creation of new adsorption sites during the simultaneous adsorption