AlPO4?ZrO2 catalysts, IV. Cyclohexene skeletal isomerization activity of systems obtained in ethylene oxide

The use of AlPO₄–ZrO₂ (weight ratio AlPO₄/ZrO₂=3) as catalyst systems obtained with ethylene oxide and subjected to different stages of heat treatments has been studied through their catalytic activity in the skeletal isomerization of cyclohexene to 1- and 3-methylcyclopentenes (1- and 3MCP). The apparent rate constants and selectivity to 1-MCP are used for an evaluation of the presence and amount of strong acid sites, the only ones capable of giving rise to skeletal isomerization. The decrease in catalytic activity as calcination increases is consistent with not only the decrease in the amount of acid sites measured vs. weaker organic bases but also with the decrease in Brönsted acidity, as shown by the decrease in O–H band intensity.

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AlPO₄–ZrO₂ ( AlPO₄/ZrO₂=3), , 1- 3- (1- 3-). 1- , . , , , O–H.

     

Oxydehydrogenation of ethylbenzene to styrene on a P?Ni?Mn based catalyst

The oxydehydrogenation of ethylbenzene to styrene over a P−Ni−Mn catalyst, has been studied in the range of 650–770 K. The kinetic behavior of the main reaction can be described by a redox type model and the oxidation of styrene with a power law. The model predictions are in good agreement with the experimental observations.     

Reversal of enantioselectivity in the asymmetric rhodium- versus iridium-catalyzed hydroboration of meso substrates

The Ir-catalyzed asymmetric hydroboration of bicyclic hydrazines with ee and chemical yields up to 64% is reported. The switch from rhodium to iridium leads systematically to opposite enantiomers in this desymmetrization reaction.     

SYNTHESES AND PROPERTIES OF POLYPHENYL-1,2,4-TRIAZINES

A series of aromatic poly--1, 2, 4-triazines have been prepared. Experimental results showedthat these polymers exhibited good thermally oxidative stability as determined by isothermal agingat 30℃for 200 hours in air. After submerging the coated wire in boiling water for 240 hours nochange in electrical insulation was detected. Polymer films also showed good tensile strength (1050-1400 kg/cm~2) at room temperature. Therefore aromatic poly-1, 2, 4-triazines demonstrate highperformance showing good potential for use as functional and structural resins in the environmentsdemanding high thermal stability and hydrolytic stability.     

RESEARCH NOTE

Abstract— The endogenous levels of indole-3-acetic acid (IAA), abscisic acid (ABA) and gibberellins (GA) were examined by gas chromatography-mass spectrometry in Prunus cerasus plantlets grown under different light conditions in relation to previous work on the photocontrol of stem elongation. The endogenous levels of free and conjugated IAA in the apical sections of red-grown shoots were about two-fold higher than those in the blue-treated plants, and these corresponded with maximum shoot elongation. By contrast, greater concentrations of ABA and GA were found in blue-grown plants compared to red with intermediate shoot growth. When blue was combined with red or far red, lower levels of IAA, ABA and GA correlated with less growth. These results suggest that the regulation of stem elongation by phytochrome and a blue-absorbing pigment may, at least in part, occur through a modulation of hormone levels.     

Soil characterization by energy dispersive X-ray fluorescence: sampling strategy for in situ analysis.

This work describes a sampling strategy that will allow the use of portable EDXRF (energy dispersive X-ray fluorescence) instruments for "in situ" soil analysis. The methodology covers a general approach to planning field investigations for any type of environmental studies and it was applied for a soil characterization study in the zone of Campana, Argentina, by evaluating data coming from an EDXRF spectrometer with a radioisotope excitation source. Simulating non-treated sampled as "in situ" samples and a soil characterization for Campana area was intended. "In situ" EDXRF methodology is a powerful analytical modality with the advantage of providing data immediately, allowing a fast general screening of the soil composition.     

Methane steam reforming over rhodium promoted Ni/Al2O3 catalysts

The effect of Rh addition upon catalyst characteristics and performance in methane steam reforming was investigated using Rh-promoted Ni/Al₂O₃ catalysts. The number of reduced metal atoms exposed on the surface increased for the Rh-promoted catalysts. Rh-promoted catalysts showed an increase in CH₄ reforming activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase in the number of metal surface atoms caused the activity enhancement. Rh also facilitated reduction of Ni/Al₂O₃.     

Sequential quantification of methyl mercury in biological materials by selective reduction in the presence of mercury(II), using two gas–liquid separators

The present procedure is based on the sequential selective reduction of mercury(II) and methyl mercury using two gas–liquid separators in series. Cold vapor atomic absorption spectrometry was used for detection. Mercury(II) is reduced by a 0.01% m/v sodium tetrahydroborate solution and driven to the absorption cell in the first separator. The methyl mercury species is reduced by the same reductant but at a 0.3% m/v concentration, and in the presence of iron(III) chloride. Parameters such as argon flow rate, and the NaBH₄ and dithiophosphoric acid diacyl ester concentrations were optimized. At the optimized conditions, and using aqueous standards for calibration, the corresponding limits of detection (3σ_b, n=10) were 400 and 600 ng l⁻¹ for mercury(II) and methyl mercury, respectively. The sample throughput was 12 h⁻¹. The procedure was used for the determination of methyl mercury in dogfish liver and dogfish muscle certified reference materials, and good concordance between found and certified values was observed.     

Simultaneous determination of aflatoxins B2 and G2 in peanuts using spectrofluorescence coupled with parallel factor analysis

In the present study a method for the simultaneous determination of aflatoxins B₂ and G₂ in peanuts has been developed. The method uses second order standard addition method and excitation–emission fluorescence data together with parallel factor analysis (PARAFAC). The aflatoxin analysis was based on extraction with methanol–water and carried out using immunoaffinity clean-up. The results of PARAFAC on a set of spiked and naturally contaminated peanuts indicated that the two aflatoxins could be successfully determined. The method was validated and analytical figures of merit were obtained for both analytes. The limits of detection (LOD) were 0.05 and 0.04 μg kg⁻¹ for aflatoxins B₂ and G₂, respectively. The limits of quantification (LOQ) were 0.16 and 0.12 μg kg⁻¹ for aflatoxins B₂ and G₂, respectively. Coupling of spectrofluorimetry with PARAFAC can be considered as an alternative method for quantification of aflatoxins in the presence of unknown interferences obtained through analysis of highly complex matrix of peanuts samples at a reduced cost per analysis.     

Alpo4 and Alpo4-Al2O3 as New Heterogeneous Catalysts for the Solvent-Free Tetrahydropyranylation of Alcohols and Phenols

OH-protection of alcohols and phenols by heating the hydroxylated compound with 3,4-dihydro-2H-pyrane in the presence of an AlPO₄ or AlPO₄-Al₂O₃ heterogeneous acid catalyst is described. Isolated yields, not optimized, were in the range 50–99%.