CO Oxidation on Cu/MgO-SiO2 Sol-Gel Derived Catalysts

Sol-gel Cu//MgOSiO₂ catalysts were prepared gelling tetraethoxysilane (TEOS), magnesium ethoxide and copper acetylacetonate at pH 3 and pH 9. The catalysts shown specific surface areas ca. 500 m²/g and 140 m²/g for pH 9 and pH 3 preparations respectively. Si(OH) and Si(OH)₂ hydroxy groups were observed by MAS-RMN spectroscopy in both preparations. CO₂-TPD and NH₃-TPD desorption thermograms showed that acid and basic sites were formed on the catalysts surface. It has been found that the catalysts having the highest density of basic sites were the catalysts showing the highest activity for the CO oxidation. It is proposed that the catalytic activity depends of the relative Cu⁼¹/Cu⁼² stability given by the support acidity.     

Certified reference material for the quality control of EDTA- and DTPA-extractable trace metal contents in calcareous soil (CRM 600)

Single extraction tests are commonly used to study the eco-toxicity and mobility of metals in soils, e.g. to assess the bioavailable metal fraction (and thus to estimate the related phyto-toxic and nutritional deficiency effects) and the environmentally accessible trace metals upon disposal of e.g. sediment on to a soil (e.g. contamination of ground waters). However, the lack of uniformity in the different procedures does not allow the results to be compared worldwide nor the procedures to be validated. This paper describes the interlaboratory testing of EDTA- and DTPA-extraction procedures for soil analysis, followed by the preparation of a calcareous soil reference material (CRM 600), the homogeneity and stability studies and the analytical work performed for the certification of the EDTA- and DTPA- extractable contents of some trace metals (following the standardized extraction procedures). Received: 21 May 1997 / Revised: 4 July 1997 / Accepted: 9 July 1997     

Determination of fluoride in complex liquid matrices by electrothermal atomic absorption spectrometry with in-furnace oxygen-assisted ashing

A new chemical method is reported for the determination of total fluoride in complex liquids and suspensions, such as fruit juices, urine, serum and blood. It is based on the formation of the A1F radical in a graphite furnace afterin situ oxygen-assisted ashing of the untreated sample. The absorbance of this radical is measured at 227.45 nm. The method is relatively easy to use and provides a low detection limit (14 ng/ml) and reasonable reproducibility (5–10%).     

Determination of metal-ligand stoichiometries for inorganic complexes using total reflection X-ray fluorescence

The methods usually used to determine the ratio metal-ligand in inorganic complexes require a set of solutions with different concentrations for both the ligand and metal. We propose a new method using the total reflection X-ray fluorescence technique, in which the ratio between metal and ligand is determined precisely, easily, and quickly. Experimental results provide evidence that for different chemical complexes, the ligand-metal ratio determined by this technique deviates at most from stoichiometric values by 6%. The technique is restricted usually to elements with Z above 14, and its detection limit is on the order of 10(-8) g/g.     

Core/valence partition and relativistic effects in effective potentials for transition metals

Two different versions, relativistic and nonrelativistic, of the “shape-consistent” effective potential (EP ) formalism are analyzed in ab initio calculations for transition metals. The influence of alternative core/valence partitions on the reliability of the procedure is discussed. The accuracy of EP results for transition metals is shown to depend on adequate choices of the valence subspace and proper inclusion of relativistic effects.     

Reactive dications: the superacid-catalyzed reactions of alkynes bearing adjacent N-heterocycles or amine groups

A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation.     

Photoinduced electron transfer in platinum(II) terpyridinyl acetylide complexes connected to a porphyrin unit

A series of six new dyads consisting of a zinc or magnesium porphyrin appended to a platinum terpyridine acetylide complex via a para-phenylene bisacetylene spacer are described. Different substituents on the 4' position of the terpyridinyl ligand were explored (OC7H15, PO3Et2, and H). The ground-state electronic properties of the dyads are studied by electronic absorption spectroscopy and electrochemistry, and they indicate some electronic interactions between the porphyrin subunit and the platinum complex. The photophysical properties of these dyads were investigated by steady-state, time-resolved, and femtosecond transient absorption spectroscopy in N,N-dimethylformamide solution. Excitation of the porphyrin unit leads to a very rapid electron transfer (2-20 ps) to the nearby platinum complex followed by an ultrafast charge recombination, thus preventing any observation of the charge separated state. The variation in the rate of the photoinduced electron transfer in the series of dyads is consistent with Marcus theory. The results underscore the potential of the para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance.     

Spectrophotometric determination of indium in nickel alloys and zinc ores with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea

A sensitive method for the spectrophotometric determination of indium with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea is proposed. A yellow complex is formed at pH 4.5 (succinate buffer) in a medium containing 40% dimethylformamide, and the absorbance is measured at 415 nm. The molar absorptivity is 6.2 x 10(4)l.mole(-1).cm(-1). The relative standard deviation of the procedure is 1.5%. The method has been applied to determination of indium in a nickel alloy and three zinc ores, with prior isolation of indium by co-precipitation with ammonia and extraction into n-butyl acetate from 5M hydrobromic acid.