Determinação de traços de Co e Co2 "em linha" por cromatografia em fase gasosa

The present work describes a rapid and sensitive method for the determination of carbon monoxide and carbon dioxide at low concentration levels, on line, in ethylene and hydrogen lines. These gases were separated in a column filled with Porapak Q, converted to methane and quantified by a flame ionization detector. Some modifications were made in the injection system and in the lines of the carrier gas. The detection limits of 2,6 ppbV and 4,85 ppbV for CO and CO2, respectively, were reached after modifications.

Reações de Cp'(CO)2MnPPH2H com CH3COCl e CH3S(O)2Cl em THF/trietilamina: evidências da primeira estabilização por complexação de um fósforo-homólogo das sulfonamidas

Cp'Mn(CO)3 (Cp'=h5-C5H4-CH 3) reacts with P(C6H5)2H in THF to give Cp'(CO)2MnPPh2H (Ph = Phenyl) (1), by substitution of one CO ligand. The reaction of 1 with CH3COCl and CH3S(O)2Cl in the presence of triethylamine occurs under electrophilic substitution on the diphenylphosphan ligand to yield the acetyl- and sulfonylphosphane complexes of manganese(I) Cp'(CO)2MnPPh2COCH3 (2) and Cp'(CO)2MnPPh2S(O)2 CH3 (3). The complex stabilisation of these molecules, wich are hitherto unknown in the free state, is only accomplished by blocking the free electron pair on phosphorus by coordination. The new complexes 1, 2 and 3 were analysed by IR, ¹H-NMR and 31P-MNR spectroscopy and their similar structures are discusssed.

Investigação espectroscópica dos carbonilos heterobimetálicos cis-[Fe(CO)4(HgX)2], X = Cl, Br,I

The series of compounds cis-[Fe(CO)4(HgX)2], X=Cl,Br,I shows an octahedral geometry around the iron atom with the two HgX groups cis to each other. In this paper the assignment for the carbonyl stretching modes and the calculation of their force constants were performed on the basis of the Cotton-Krainhanzel model. Taking into account all the data from the IR, 199Hg NMR and UV-vis spectra it is possible to verify the influence of X on the electronic densities at the metallic centers.

Caracterização de catalisadores Cu/CeO2/Al2O3 por redução a temperatura programada e atividade para oxidação de CO

The kinetic parameters for the CO oxidation reaction using copper/alumina-modified ceria as catalysts were determined. The catalysts with different concentrations of the metals were prepared using impregnation methods. In addition, the reduction-oxidation behaviour of the catalysts were investigated by temperature-programmed reduction. The activity results show that the mechanism for CO oxidation is bifunctional : oxygen is activated on the anionic vacancies of ceria surface, while carbon monoxide is adsorbed preferentially on the higher oxidation copper site. Therefore, the reaction occurs on the interfacial active centers. Temperatures-programmed Reduction patterns show a higher disperdion when cerium oxide is present.

A síntese do aduto binuclear [Fe(CNBu t)(CO)4(HgSO4 )]

The binuclear [Fe(CNBu t)(CO)4(HgSO4 )] adduct was obtained in the reaction of HgSO4 with [Fe(CNBu t)(CO)4] in methanol. This adduct, without a similar in the homoleptic pentacarbonyliron, was characterized by analytical and spectroscopic data. Further Mössbauer and molar conductivity studies have confirmed it's adduct nature.

Estudos da deposição em subtensão de cádmio sobre ouro policristalino na presença de diferentes ânions co-adsorvidos

Cadmium UPD on Au was studied by voltammetric and microgravimetric measurements. In the oxide formation/reduction potential region, a mass increasing/decreasing of 32 ng cm-2 was associated to incorporation/elimination of one oxygen per active site. The modifications promoted in the voltammetric and mass profiles by 10-5 M Cd(ClO4)2 are restricted to potentials more negative than 0.4 V. After a 120 s potential delay at 0.05 V, the positive sweep reveals an anodic peak with charge of 40 muC cm-2 and mass decrease of 22 ng cm-2, associated to Cd ads dissolution. Sulphate or chloride was added to the solution without significant influence, due to the low coverage with Cd or anions.

Espectroscopia vibracional: sistemática para o cálculo dos estiramentos CO de complexos carbonílicos e determinação da sua atividade IV e Raman

IR bands related to M-C stretchings are not diagnostically significant for the identification of carbonyl groups in the spectra of carbonyl complexes. Otherwise, the frequency, intensity and number of bands for the CO stretchings provide very useful informations about the number of CO ligands and many others structural proprieties, like the presence of bridged CO groups. We report about a relatively simple and useful method for the determination of the CO stretchings of carbonyl complexes, which considers only the bond stretching internal coordinates of the CO groups.

Caracterização de amostras comerciais de vermicomposto de esterco bovino e avaliação da influência do pH e do tempo na adsorção de Co(II), Zn(II) and Cu(II)

Some commercial samples of vermicompost from bovine manure (humus) were characterized by thermogravimetry with respect to humidity, organic matter and ash contents, the percentages of which range from 6.55 to 5.35%, 53.01 to 69.96% and 46.44 to 66,14%, respectively. The capacity of adsorption of Cu2+, Zn2+ and Co2+ ions by these samples has been evaluated as a function of pH and time. The contents of several metal ions in the original vermicompost samples have been determined by flame atomic absorption spectrometry after digestion in a microwave oven. The high nitrogen content suggests that the earthworms used in the maturation procedure lead to an efficient degradation of organic matter. The metal retention was affected by both pH and adsorption time. The results also show that adsorption follows the order Cu2+ > Zn2+ > Co2+.

Análise teórica da interação de CO, CO2 e NH3 com ZnO

This paper presents a study of the interaction of small molecules with ZnO surfaces by means of theoretical methods. The AM1 semi-empirical method was used for optimizing the geometric parameters of adsorbed molecules. The optimized AM1 structures were used in the calculations of the ab initio RHF method with the 3-21G* basis set. The interaction of CO, CO2 and NH3 molecules were studied with (ZnO)22 and (ZnO)60 cluster models. We have analyzed the interaction energy, SCF orbital energies, Mulliken charges and the density of states (DOS).

Emprego de óxidos tipo perovskita nas oxidações do propano e CO

Simultaneous oxidation/co-precipitation of an equimolar mixture of La(III) and Co(II) nitrates and La(III) nitrate and Mn(II) chloride afforded a hydroxide gel, which was converted to LaCoO3 and LaMnO3 on calcination at 600 °C. After calcination, the obtained perovskites have been characterised by X-ray diffraction (XRD), X- ray photoelectron spectroscopy (XPS), thermogravimetric analysis (DTA - TGA) and BET specific surface determination. Specific surface areas of perovskites were 12 - 60 m²/g. XRD analysis showed that LaCoO3 and LaMnO3 are simple phase perovskite - type oxides. Traces of LaOCl, in addition to the perovskite were detected in the LaMnO3. The catalytic behavior was examined in the propane and CO oxidation. The LaCoO3 catalyst was more active to CO2 than the LaMnO3 catalyst.

Estratégias de cultivo para produção dos plásticos biodegradáveis poli(3-Hidroxibutirato) e poli(3-hidroxibutirato-co-3-hidroxivalerato) por bactérias

Polyhydroxyalkanoates (PHAs) are carbon and energy storage materials that are accumulated as intracellular granules in a variety of microorganisms during unbalanced growth. PHAs have drawn attention due to their properties similar to conventional plastics and complete biodegradability. They can be used for food and cosmetics packaging, and in medicine and agriculture. However, their applicability is reduced because of their high production cost compared to conventional plastics. An overview on production strategies of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) aiming at reducing the production costs is presented.

ZAC Éco-quartier Les Fonses Bois Vieux, Villeneuve-Tolosane

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Efeito do teor metálico em catalisadores Co/Al2O3 aplicados à reação de reforma a vapor de etanol

The development of cobalt catalysts to produce hydrogen from ethanol is the goal of this investigation. Co/Al2O3 catalysts were prepared by impregnation and characterized by atomic absorption, nitrogen adsorption, X-ray diffraction, Raman spectroscopy, temperature programmed reduction and carbon analysis. The catalysts contained Co3O4 oxide and Co3+ and Co2+ species interacting with alumina. The cobalt load affects the crystal size and the crystalline structure and higher Co loads influence the reaction mechanism, changing the selectivity of the catalysts, decreasing the amount of CO produced and avoiding the formation of products catalyzed by the support. The ethanol conversion was 50-70% with 10-<1% of CO in the hydrogen.

Cu and Co exchanged ZSM-5 zeolites: activity towards no reduction and hydrocarbon oxidation

|Cu x|[Si yAl]-MFI and |Co x|[Si yAl]-MFI catalysts were prepared by ion exchange from |Na|[Si yAl]-MFI zeolites (y = 12, 25 and 45). The activity of the catalysts was evaluated in the reduction of NO to N2 in an oxidative atmosphere using propane or methane as reducing agents. The Cu catalysts were only active with propane and they presented higher activity than the Co-based catalysts, the latter being active with both hydrocarbons. H2-TPR and DRS-UV/Vis data allowed correlation between the activity towards NO reduction and the presence of cationic charge-compensating species in the zeolite. It was also verified that the hydrocarbons are preferentially oxidised by O2, a reaction that occurs simultaneously with their oxidation with NO.

Estudos Cinéticos da aquação do trans-[Co(en)2Cl2]Cl

The trans-dichlorobis(ethylenediamine)cobalt(III) chloride was synthesized in an undergraduate laboratory and its aquation reaction was carried out at different temperatures. This reaction follows pseudo-first-order kinetics and the rate constants, determined at 25, 35, 45, 55 and 70 º C, are 1.44 x 10-3; 5.14 x 10-3; 1.48 x 10-2; 4.21 x 10-2 and 2.21 x 10-1 s-1, respectively. The activation energy is 93.99 ± 2.88 kJ mol-1.