Uma proposta de síntese para o ensino integrado das disciplinas experimentais de química orgânica e inorgânica nos cursos de graduação

The synthesis of the layered compound VO(PO4)(H2O)2 and its use to oxidize 2-butanol to the ketone 2-butanone, is proposed as an experiment to integrate the organic and inorganic experimental undergraduate chemistry courses, in an atempt to overcome the observed disrupture between organic and inorganic chemistry.

Desidrogenação do etilbenzeno sobre compostos de ferro e alumínio

Chromium and potassium-doped iron oxides are widely used as industrial catalysts in the dehydrogenation of ethylbenzene to produce styrene. They have several advantages but deactivate with time, because of the loss of potassium. Also, they are toxic due to chromium compounds. Therefore there is a need for developing alternative non toxic catalysts without potassium. Then, iron and aluminum compounds were prepared by different methods in this work. Different phases were produced depending on the preparation method. Aluminum-doped hematite was more active and selective to styrene than the aluminum ferrite. Aluminum acts both as textural and structural promoter in the catalysts.

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.

Caracterização por XPS de filmes passivos formados sobre aços de baixa liga em meio de bicarbonato

Passive films formed in bicarbonate solutions on carbon steel, chromium steel and high speed steel have been characterized by XPS. The passive films formed on chromium and high speed steels showed superior protective properties than those formed on carbon steel. It was confirmed by XPS that the steel composition influences the passive film composition. Chromium oxide and hydroxide, as well as molybdenum and tungsten oxides and hydroxides are present in the passive film of chromium steel and high speed steel, respectively, besides iron oxide and hydroxide. The more complex composition of the oxide film on high speed steel explains its electrochemical behaviour and highest corrosion resistance.

Óxidos de ferro e monazita de areias de praias do Espírito Santo

Sand samples collected from two sampling sites on Guarapari and Iriri beaches, state of Espírito Santo, Brazil, were studied in an attempt to better describe their chemical and mineralogical compositions and radioactive behaviors. The sands were found to contain about 6 (Guarapari) and 2 dag kg-1 (Iriri) of rare earth and thorium that, if allocated to the monazite-(Ce) structure, lead to the averaged formulae Ce3+0,494Gd3+0,012La3+0,209Nd3+0,177Pr3+0,040Sm3+0,024Th4+0,033 (PO4) and Ce3+0,474La3+0,227Nd3+0,190Pr3+0,044Sm3+0,032Th4+0,024 (PO4). From Mössbauer spectroscopy data, the magnetic fractions of these sands were found to contain stoichiometric hematite (47.4 dag kg-1, from Guarapari, and 25.1 dag kg-1, from Iriri) and magnetite (44.1 and 58.8 dag kg-1). The specific alpha and beta radiation activities were also measured for both samples.

Materiais magnéticos baseados em diferentes zeólitas para remoção de metais em água

In this work the adsorption features of zeolites (NaY, Beta, Mordenite and ZSM-5) have been combined with the magnetic properties of iron oxides in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbents for contaminants in water and subsequently removed from the medium by a simple magnetic process. The magnetic zeolites were characterized by XRD, magnetization measurements, chemical analyses, N2 adsorption isotherms and Mössbauer spectroscopy. These magnetic adsorbents show remarkable adsorption capacity for metal ion contaminants in water.

Adsorção de As, Cu, Pb e Cr na avaliação da capacidade de fixação de metais por resíduo de mineradoras de ferro

Two samples of residues from iron mining plants have been investigated for their retention capacity of As, Cu, Cr, and Pb. The sample with the higher content of iron oxides showed the highest capacity to retain metals. The adsorption affinity series changes from Pb>Cu>Cr~As to As>Pb>Cu>Cr or As>Cu>Cr>Pb, depending on the material and the concentration of the initial solution. In the competitive environment, the Pb adsorption decreases and the As, Cu and Cr adsorption increases. Sequential extraction procedures, carried out after adsorption batch experiments, showed that the most important adsorption process occurs in the oxide fraction and that the major part of the absorbed metal is remobilized from exchangeable and oxide fractions.

Adsorção de glifosato sobre solos e minerais

Glyphosate, an enzyme inhibitor herbicide, has been widely used around the world in agriculture. Dr. John Franz from Monsanto Corporation (USA) discovered glyphosate in 1970. It has been showed that glyphosate is strongly adsorbed by inorganic soil components especially aluminium and iron oxides, and the phosphate group is involved in this interaction. The inactivation of glyphosate in soils can last for days or even months depending on soil characteristics. The addition of phosphate from fertilizers can displace glyphosate from the soils and this could be the cause of decreased productivity of some crops.

Síntese e caracterização de perovskitas LaNi(1-x)Co xO3 como precursores de catalisadores para a conversão do metano a gás de síntese pela reforma com CO2

LaNiO3 perovskite was modified by partial substitution of nickel by cobalt in order to increase the stability and resistance to carbon deposition during the methane CO2 reforming. The results showed that a suitable combination of precipitation and calcination steps resulted in oxides with the desired structure and with important properties for application in heterogeneous catalysis. The partial substitution of Ni by Co resulted in lower rates of conversion of both the reactants, but the catalyst stability was highly increased. The LaNi0.3Co0.7O3 catalyst, calcined at 800 ºC, was the most active under the reaction conditions.

Diagramas de Ellingham e de Van't Hoff: algumas considerações

The main subject of this article is to show the parallelism betwen the Ellingham and Van't Hoff diagrams. The first one is a graphic representation of the changes in the standard Gibbs free energy (deltarGtheta) as a function of T and was introduced by Ellingham in 1944, in order to study metallurgic processes involving oxides and sulphides. On the other hand, the Van't Hoff diagram is a representation of the function ln K versus (1/T). The equivalence between both diagrams is easily demonstrated, making simple mathematical manipulations. In order to show the parallelism between both diagrams, they are presented briefly and two examples are discussed. The comparison of the both diagrams surely will be helpful to students and teachers in their learning and teaching activities, and will certainly enrich important aspects of chemical thermodynamics.

Redução catalítica seletiva de óxidos de nitrogênio sobre hematita contendo cobre

The activity of copper-doped hematite in the SCR with propane, in the presence of oxygen, was evaluated in this work. It was found that copper sulfate led to the production of solids with different specific surface areas depending on the amount of copper. The sulfur and copper species were mainly located on the surface. The copper-containing catalysts were more active in the reduction of nitrogen oxides and less active in the propane oxidation as compared to pure hematite. This behavior was assigned to an association of both sulfur and copper species to produce new sites active for NO reduction.

Estudo da oxidação total do etanol usando óxidos tipo perovskita LaBO3 (B= Mn, Ni, Fe)

The present work investigated the effect of coprecipitation-oxidant synthesis on the specific surface area of perovskite-type oxides LaBO3 (B= Mn, Ni, Fe) for total oxidation of ethanol. The perovskite-type oxides were characterized by X-ray diffraction, nitrogen adsorption (BET method), thermogravimetric analysis (TGA-DTA), TPR and X-ray photoelectron spectroscopy (XPS). Through method involving the coprecipitation-oxidant was possible to obtain catalysts with different BET specific surface areas, of 33-51 m²/g. The results of the catalytic test confirmed that all oxides investigated in this work have specific catalytic activity for total oxidation of ethanol, though the temperatures for total conversion change for each transition metal.

Compósitos magnéticos baseados em hidrotalcitas para a remoção de contaminantes aniônicos em água

In this work the adsorption features of hydrotalcites (Al, Mg- CO3) and the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. The magnetic hydrotalcites were characterized by XRD, magnetization measurements, N2 adsorption isotherms and Mössbauer spectroscopy. These magnetic adsorbents show remarkable adsorption capacity for anionic contaminants in water.

Uma estratégia adaptada para síntese de magnetita

Chemical reactions in the solid state are often not included in undergraduate chemistry curricula, due to requirements for special laboratory facilities such as ovens and precision weighing balances. This work aims to describe novel and relatively simple magnetite chemical syntheses in dry medium, which could also be used as an alternative for freshmen chemistry experiments. The proposed reaction was carried out in a muffle furnace by heating (i) a sol-gel preparation and (ii) natural hematite, under nitrogen atmosphere at 400 ºC. The synthesized magnetite was characterized with powder X-ray diffraction and Mössbauer spectroscopy. Results show that magnetite samples have chemical properties as well as crystalline structure quite similar to those of standard natural magnetite.

Nióbia magnética como adsorvente de contaminantes orgânicos em meio aquoso: efeito da temperatura e do pH

This work describes novel materials based on pure iron oxide and iron oxide/niobia composite to produce a magnetic adsorbent. These materials were prepared with synthetic iron oxide and characterized by powder XRD, SEM, FTIR, TPR and Mössbauer spectroscopy. Results showed that the main iron oxides formed were goethite (aFeOOH) and maghemite (gFe2O3) with small particle size. The iron oxide and iron oxide/niobia composite showed high adsorption ability for organic compounds. The positive enthalpy indicated an endothermic adsorption process suggesting physical adsorption.