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Metal Loading (metal + loading)
Selected AbstractsEnhanced dechlorination of trichloroethylene by membrane-supported Pd-coated iron nanoparticlesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2008Linfeng Wu Abstract In this study, cellulose acetate (CA) supported iron and Pd/Fe nanoparticles were used for dechlorination of trichloroethylene (TCE) from water. Solution and microemulsion methods were used to synthesize the iron nanoparticles. Pd/Fe bimetallic particles were prepared by postcoating Pd on the prepared iron nanoparticles. These materials were then dispersed in CA solution, which was used to prepare the membrane-supported nanoparticles. TEM imaging confirmed that the iron and Pd/Fe bimetallic nanoparticles were ,10 nm in diameter. The results of dechlorination studies showed that the surface composition of the Pd/Fe bimetallic nanoparticles (microemulsion method) significantly affected the observed reduction rate constant. In addition, the rate constant was a nonlinear function of metal loading and initial TCE concentration. A comparative study for the Pd/Fe (Pd 1.9 wt %) nanoparticles from solution and microemulsion methods showed that the nanoparticles formed by the latter method gave superior performance for the dechlorination of TCE. © 2008 American Institute of Chemical Engineers Environ Prog, 2008 [source] Hydrogenation of Phenol in Supercritical Carbon Dioxide Catalyzed by Palladium Supported on Al-MCM-41: A Facile Route for One-Pot Cyclohexanone FormationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009M. Chatterjee Abstract The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50,°C over palladium supported Al-MCM-41 (metal loading ,1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (,98%), an industrially important compound, in a "one-pot" way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is validated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by <19,kcal,mol,1 over cyclohexanol in scCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10,20,nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds. [source] Pyrazole functionalized organo-ceramic hybrids for noble metal separationsAICHE JOURNAL, Issue 10 2005Jun S. Lee Abstract A series of pyrazole-functional adsorbents is synthesized by sol,gel processing technology and used to study the extraction characteristics for palladium, platinum, and gold chlorides from leaching solutions. An organosilicon compound, N-(trimethoxysilylpropyl)-pyrazole, is synthesized as the functional precursor for these adsorbents. Hydrothermal treatments for the gelled materials alter pore characteristics without chemical property changes. To study adsorptive extraction of Pd(II), Pt(IV), and Au(III) chlorides, the hydrothermally treated adsorbent is used. The experimental results show that this adsorbent has high Pd(II) uptake capacity (1.41 mmol/g), strong selectivity for Pd(II) chloride over Pt(IV) and Au(III) chlorides, and no reactivity for Cu(II) and Fe(II) in 2.0 M HCl solutions. The material also has sustainable stability over repeated metal loading and stripping in a short column. In addition to the experimental studies, the adsorption processes in batch and packed column systems are successfully modeled by using a pore diffusion model and presented. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Copper, zinc, and cadmium accumulation in two prairie soils and crops as influenced by repeated applications of manure,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2007Sarah L. Lipoth Abstract A study was conducted to determine the effect of repeated (5,7 y) annual application of liquid swine or solid cattle manure on the plant availability of copper (Cu), zinc (Zn), and cadmium (Cd) at two field sites in the W-central and E-central agricultural regions of Saskatchewan, Canada. Soil samples, plant-straw and grain samples from the 2003 growing season were collected and analyzed for total Cu, Zn, and Cd concentrations using nitric acid microwave digestion followed by atomic-absorption spectroscopy. An ammonium bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA) extraction was performed on the soil samples as a measure of the plant-available fraction. Crop plants that were tested included wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). The results of this study indicated that long-term repeated applications of manure fertilizer sometimes resulted in increased plant availability of Cu, Zn, and Cd, as reflected in increased concentrations of the plant-available metal observed both in the soil and plant tissue. In the case of Cu and Zn, these increases were related to the rate of application, as the manure is a source of Cu and Zn. Changes in soil conditions from repeated manure application, including a decrease in pH and stimulated plant-root growth can explain the effect that both manure and urea-fertilizer application had on increasing the Cd concentration in the plant. Overall, there does not appear to be any concern about soil metal loading and plant accumulation in these soils after 5,7 y of manure application, as soil and plant concentrations were well below the allowable limits. [source] Ethylene polymerization over MgO-supported zirconocene catalystsPOLYMER ENGINEERING & SCIENCE, Issue 5 2003Soo Jin Kim Supported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes. [source] Azotobacter vinelandii Metal Storage Protein: "Classical" Inorganic Chemistry Involved in Mo/W Uptake and Release ProcessesCHEMBIOCHEM, Issue 4 2008Jörg Schemberg Dr. Abstract The release of Mo (as molybdate) from the Mo storage protein (MoSto), which is unique among all existing metalloproteins, is strongly influenced by temperature and pH value; other factors (incubation time, protein concentration, degree of purity) have minor, though significant effects. A detailed pH titration at 12,°C revealed that three different steps can be distinguished for the Mo-release process. A proportion of ,15,% at pH 6.8,7.0, an additional 25,% at pH 7.2,7.5 and ca. 50,% (up to 90,% in total) at pH 7.6,7.8. This triphasic process supports the assumption of the presence of different types of molybdenum-oxide-based clusters that exhibit different pH lability. The complete release of Mo was achieved by increasing the temperature to 30,°C and the pH value to >7.5. The Mo-release process does not require ATP; on the contrary, ATP prevents, or at least reduces the degree of metal release, depending on the concentration of the nucleotide. From this point of view, the intracellular ATP concentration is suggested to play,in addition to the pH value,an indirect but crucial role in controlling the extent of Mo release in the cell. The binding of molybdenum to the apoprotein (reconstitution process) was confirmed to be directly dependent on the presence of a nucleotide (preferably ATP) and MgCl2. Maximal reincorporation of Mo required 1 mM ATP, which could partly be replaced by GTP. When the storage protein was purified in the presence of ATP and MgCl2 (1 mM each), the final preparation contained 80 Mo atoms per protein molecule. Maximal metal loading (110,115 atoms/MoSto molecule) was only achieved, if Mo was first completely released from the native protein and subsequently (re-) bound under optimal reconstitution conditions: 1 h incubation at pH 6.5 and 12,°C in the presence of ATP, MgCl2 and excess molybdate. A corresponding tungsten-containing storage protein ("WSto") could not only be synthesized in vivo by growing cells, but could also be constructed in vitro by a metalate,ion exchange procedure by using the isolated MoSto protein. The high W content of the isolated cell-made WSto (,110 atoms/protein molecule) and the relatively low amount of tungstate that was released from the protein under optimal "release conditions", demonstrates that the W-oxide-based clusters are more stable inside the protein cavity than the Mo-oxide analogues, as expected from the corresponding findings in polyoxometalate chemistry. The optimized isolation of the W-loaded protein form allowed us to get single crystals, and to determine the crystal X-ray structure. This proved that the protein contains remarkably different types of polyoxotungstates, the formation of which is templated in an unprecedented process by the different protein pockets. (Angew. Chem. Int. Ed.2007, 46, 2408,2413). [source] Enhanced Cooperativity in Hydrolytic Kinetic Resolution of Epoxides using Poly(styrene) Resin-Supported Dendronized Co-(Salen) CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Poorva Goyal Abstract Excellent enantioselectivities and isolated yields have been achieved for the hydrolytic kinetic resolution of epoxides using a resin-supported dendronized R,R-(salen)Co catalyst with catalyst loadings as low as 0.04 mol%, the lowest metal loadings of any heterogeneous resin-supported (salen)Co catalyst reported to date. In addition, the supported catalysts can be recycled and reused with comparable enantioselectivities. It is hypothesized that the high catalytic activity can be attributed to the flexible linker and the dendronized framework supporting the (salen)Co moieties on the resin thereby promoting cooperativity between two metal centers. This work opens up new opportunities for the design of highly active resin-supported catalysts that catalyze transformations through a bimetallic pathway. [source] MODELING METALS TRANSPORT AND SEDIMENT/WATER INTERACTIONS IN A MINING IMPACTED MOUNTAIN STREAM,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2004Brian S. Caruso ABSTRACT: The U.S. Environmental Protection Agency (USEPA) Water Quality Analysis Simulation Program (WASP5) was used to model the transport and sediment/water interactions of metals under low flow, steady state conditions in Tenmile Creek, a mountain stream supplying drinking water to the City of Helena, Montana, impacted by numerous abandoned hard rock mines. The model was calibrated for base flow using data collected by USEPA and validated using data from the U.S. Geological Survey (USGS) for higher flows. It was used to assess metals loadings and losses, exceedances of Montana State water quality standards, metals interactions in stream water and bed sediment, uncertainty in fate and transport processes and model parameters, and effectiveness of remedial alternatives that include leaving contaminated sediment in the stream. Results indicated that during base flow, adits and point sources contribute significant metals loadings to the stream, but that shallow ground water and bed sediment also contribute metals in some key locations. Losses from the water column occur in some areas, primarily due to adsorption and precipitation onto bed sediments. Some uncertainty exists in the metal partition coefficients associated with sediment, significance of precipitation reactions, and in the specific locations of unidentified sources and losses of metals. Standards exceedances are widespread throughout the stream, but the model showed that remediation of point sources and mine waste near water courses can help improve water quality. Model results also indicate, however, that alteration of the water supply scheme and increasing base flow will probably be required to meet all water quality standards. [source] | |||||||||||||