Search results for "medium"
showing 10 items of 3746 documents
Identifying Iron-Bearing Nanoparticle Precursor for Thermal Transformation into the Highly Active Hematite Photo-Fenton Catalyst
2020
Funding: This reseach was funded by the European Regional Development Fund within the Activity 1.1.1.2 “Post-doctoral Research Aid” of the Specific Aid Objective 1.1.1 “To increase the research and innovative capacity of scientific institutions of Latvia and the ability to attract external financing, investing in human resources and infrastructure” of the Operational Programme “Growth and Employment” (No. 1.1.1.2/VIAA/1/16/157).
X-ray Photoelectron-spectroscopy Investigation of Pumice-supported Nickel-catalysts
1995
Pumice-supported nickel catalysts, prepared by the method of slow homogeneous precipitation with urea, were analysed by x-ray photoelectron spectroscopy (XPS). By comparison with similarly prepared silica- and alumina-supported nickel catalysts, a preferential interaction of Ni2+ with Al3+ of the support has been determined. A quantitative XPS analysis indicated large segregation of nickel to the surface. The treatment with H2 at 673 K and 1073 K produced a partial reduction of Ni+2 to Ni0. The extent of the reduction was largest at 1073 K and in this case the reduced Ni in the metallic phase was detectable by x-ray diffraction. A decrease of the Ni 2p/Si 2p intensity ratio occurring in the…
Understanding the Stability and Recrystallization Behavior of Amorphous Zinc Phosphate
2021
Zinc phosphate, an important pigment in phosphate conversion coatings, forms protective films on rubbing surfaces. We have simulated the underlying reactions under shear by ball-milling zinc phosphate and monitored the reaction of hopeite (Zn3(PO4)2·4H2O) and the retarded recrystallization of the amorphous reaction product by powder X-ray diffraction (PXRD) and quantitative infrared (IR) spectroscopy. Abrasion of stainless steel was simulated by addition of pure 57Fe. The results provide insight into the chemistry of phosphate conversion coatings or during battery cycling of metal phosphates and give theoretical guidance for the preparation of amorphous phosphates. Thermal analysis revealed…
The Effect of Interferences on the Uptake of Heavy Metals by Sodium (iron) Titanates from Waste Water
2007
Sodium hexatitanate, sodium trititanate, sodium nonatitanate, and a new iron doped sodium nonatitanate were synthesized. Common interferences present in waste waters that hinder the removal of heavy metals by these ion exchangers were investigated. The presence of K+, Mg2+ and Ca2+ at 0.001-0.05 M concentration had minor effect on the amount of Pb2+, Cr3+, and Ni2+ uptake. EDTA on the other hand, interferes tremendously with the metal uptake. Both in ternary and in single system, the selectivity series is in the order: Pb2+>Cr3+>Ni2+. This order changed to Cr3+>Pb2+>Ni2+, in the presence of 0.001-0.1 M EDTA at pH 5.
Nanolayered Cobalt-Molybdenum Sulfides as Highly Chemo- and Regioselective Catalysts for the Hydrogenation of Quinoline Derivatives
2018
[EN] Herein, a general protocol for the preparation of a broad range of valuable N-heterocyclic products by hydrogenation of quinolines and related N-heteroarenes is described. Interestingly, the catalytic hydrogenation of the N-heteroarene ring is chemoselectively performed when other facile reducible functional groups, including alkenes, ketones, cyanides, carboxylic acids, esters, and amides, are present. The key to successful catalysis relies on the use of a nanolayered cobalt-molybdenum sulfide catalyst hydrothermally synthesized from earth-abundant metal precursors. This heterogeneous system displays a tunable composition of phases that allows for catalyst regeneration. Its catalytic …
Sorption of uranium(VI) onto ferric oxides in sulfate-rich acid waters.
2003
The mechanisms of the uranium(VI) sorption on schwertmannite and goethite in acid sulfate-rich solutions were studied by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The samples were prepared under N2 atmosphere and initial uranium(VI) concentrations of 1 x 10(-5) (pH 6.5) to 5 x 10(-5) M (pH 4.2). The ionic strength was adjusted using 0.01 M Na2SO4 or 0.01 M NaClO4, respectively. The EXAFS structural parameters for uranium(VI) sorbed on goethite in sulfate-rich, acid and near-neutral solutions indicate that uranium(VI) forms an inner-sphere, mononuclear, bidentate surface complex. This complex is characterized by a uranium-ferric-iron distance of approximately 3.45 A. Ura…
Organic solvent-soluble contents of nickel and cobalt in some algae
1990
In pursuit of our work on metal contents of lipid fractions isolated from plant material, we now show by means of highly sensitive analytical methods that nickel and cobalt are also present in organic extracts of algae in detectable amounts
Versuche zur Herstellung linolsäurearmen Ölsäureesters über eine Hydrierung mit Palladium
1980
Uber eine Hydrierung mit Palladium auf Aktivkohle konnen geringe Gehalte an Linolsaure in Gegenwart eines hohen Olsaureuberschusses recht selektiv reduziert werden. Der Linolsauregehalt eines Fettsauremethylestergemisches wurde von 10% auf 2% gesenkt, dabei entstanden 3% cis-, 4% trans-Monoenfettsauren sowie 1% Stearinsaure. The Preparation of Oleic Ester with Reduced Linoleic Acid Content by Hydrogenation with Palladium By hydrogenation with palladium on charcoal low contents of linoleic acid can be reduced quite selectively in the presence of an excess of oleic acid ester. In a mixture of fatty acid methylesters the content of linoleic acid was reduced from 10% to 2% with the formation of…
Soluble/MOF-Supported Palladium Single Atoms Catalyze the Ligand-, Additive-, and Solvent-Free Aerobic Oxidation of Benzyl Alcohols to Benzoic Acids.
2021
Metal single-atom catalysts (SACs) promise great rewards in terms of metal atom efficiency. However, the requirement of particular conditions and supports for their synthesis, together with the need of solvents and additives for catalytic implementation, often precludes their use under industrially viable conditions. Here, we show that palladium single atoms are spontaneously formed after dissolving tiny amounts of palladium salts in neat benzyl alcohols, to catalyze their direct aerobic oxidation to benzoic acids without ligands, additives, or solvents. With this result in hand, the gram-scale preparation and stabilization of Pd SACs within the functional channels of a novel methyl-cystein…
Linear Triphosphines as Ligands for Metal Complexes Immobilization in Ionic Liquids: Palladium-Catalyzed Methoxylation of Alkynes
2012
Several novel palladium triphosphine complexes have been synthesized and tested as recyclable catalysts for the methoxylation of alkynes into acetals in ionic liquids. A complete conversion of phenylacetylene was achieved with only 0.2% of (Pd(Triphos)NCMe)((PF6)2) in a methanol/(BMIM)(BF4) mixture. We discovered that the addition of an ionic liquid to methanol allowed not only to increase the activity of the palladium catalyst but also to provide a recyclable catalyst which can be reused several times with a weaker drop of activity. To complete these catalytic studies, we describe the synthesis of the first poor -electron-donating/strong -electron-acceptor linear Triphosphine which, afte…