Propriedades texturais e catalíticas de óxidos de ferro contendo cromo e cobre

Chromium and copper-doped hematites were prepared with the aim of studying the synergistic effect of these dopants on the textural and on the catalytic properties of the iron oxides towards the high temperature shift reaction. It was found that the most active catalysts were those with the highest amount of copper. They had the Fe(II)/Fe(III) ratio near the stoichiometric value of magnetite, the highest surface areas under the reactional atmosphere and the greatest tendency to produce the active form; they also were poorly crystalline solids. The best performance was shown by the catalyst with Fe/Cu=10, heated at 300ºC. It can thus be concluded that copper acts both as textural and structural promoter in these 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.

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.

Materiais SiO2-TiO2 para a degradação fotocatalítica de diuron

SiO2-TiO2 materials prepared by sol-gel method were evaluated in the photocatalytic degradation of diuron. The materials were prepared with and without surfactant cetyltrimethylammonium chloride at different temperatures (25, 50 and 100 ºC). The samples were characterized by N2 adsorption-desorption measurements, scanning electron microscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy and infrared diffuse reflectance spectroscopy. The results showed that the materials synthesized with the surfactant had higher surface areas and band-gap values similar to anatase. All materials were more active than the commercial catalyst P-25 and better performance was achieved using the surfactant in the material synthesis.

SYNGAS PRODUCTION FROM CO2-REFORMING OF CH4 OVER SOL-GEL SYNTHESIZED Ni-Co/Al2O3-MgO-ZrO2 NANOCATALYST: EFFECT OF ZrO2 PRECURSOR ON CATALYST PROPERTIES AND PERFORMANCE

Ni-Co/Al2O3-MgO-ZrO2 nanocatalyst with utilization of two different zirconia precursors, namely, zirconyl nitrate hydrate (ZNH) and zirconyl nitrate solution (ZNS), was synthesized via the sol-gel method. The physiochemical properties of nanocatalysts were characterized by XRD, FESEM, EDX, BET and FTIR analyses and employed for syngas production from CO2-reforming of CH4. XRD patterns, exhibiting proper crystalline structure and homogeneous dispersion of active phase for the nanocatalyst ZNS precursor employed (NCAMZ-ZNS). FESEM and BET results of NCAMZ-ZNS presented more uniform morphology and smaller particle size and consequently higher surface areas. In addition, average particle size of NCAMZ-ZNS was 15.7 nm, which is close to the critical size for Ni-Co catalysts to avoid carbon formation. Moreover, FESEM analysis indicated both prepared samples were nanoscale. EDX analysis confirmed the existence of various elements used and also supported the statements made in the XRD and FESEM analyses regarding dispersion. Based on the excellent physiochemical properties, NCAMZ-ZNS exhibited the best reactant conversion across all of the evaluated temperatures, e.g. CH4 and CO2 conversions were 97.2 and 99% at 850 ºC, respectively. Furthermore, NCAMZ-ZNS demonstrated a stable yield with H2/CO close to unit value during the 1440 min stability test.

Lanthanum based high surface area perovskite-type oxide and application in CO and propane combustion

The perovskite-type oxides using transition metals present a promising potential as catalysts in total oxidation reaction. The present work investigates the effect of synthesis by oxidant co-precipitation on the catalytic activity of perovskite-type oxides LaBO3 (B= Co, Ni, Mn) in total oxidation of propane and CO. The perovskite-type oxides were characterized by means of X-ray diffraction, nitrogen adsorption (BET method), thermo gravimetric and differential thermal analysis (ATG-DTA) and X-ray photoelectron spectroscopy (XPS). Through a method involving the oxidant co-precipitation it's possible to obtain catalysts with different BET surface areas, of 33-44 m²/g, according the salts of metal used. The characterization results proved that catalysts have a perovskite phase as well as lanthanum oxide, except LaMnO3, that presents a cationic vacancies and generation for known oxygen excess. The results of catalytic test showed that all oxides have a specific catalytic activity for total oxidation of CO and propane even though the temperatures for total conversion change for each transition metal and substance to be oxidized.

Determination of piglets’ rectal temperature and respiratory rate through skin surface temperature under climatic chamber conditions

ABSTRACT In animal farming, an automatic and precise control of environmental conditions needs information from variables derived from the animals themselves, i.e. they act as biosensors. Rectal temperature (RT) and respiratory rate (RR) are good indicators of thermoregulation in pigs. Since there is a growing concern on animal welfare, the search for alternatives to measure RT has become even more necessary. This research aimed to identify the most adequate body surface areas, on nursery-phase pigs, to take temperature measurements that best represent the correlation of RT and RR. The main experiment was carried out in a climate chamber with five 30-day-old littermate female Landrace x Large White piglets. Temperature conditions inside chamber were varied from 14 °C up to 35.5 °C. The measurements were taken each 30 minutes, over six different skin regions, using a temperature data logger Thermochron iButton® - DS1921G (Tb) and an infrared thermometer (Ti). As shown by the results, the tympanic region is the best one for RT and RR monitoring using an infrared thermometer (TiF). In contrast, when using temperature sensors, the ear (TbE) is preferred to be used for RT predictions and the loin region (TbC) for RR.

New record and larval habitats of Culex eduardoi (Diptera: Culicidae) in an irrigated area of Patagonia, Chubut Province, Argentina

The object of the present work was to identify the larval habitats of Culex eduardoi and to determine the microenvironmental conditions related to their presence in different artificial freshwater environments (temporary, semi-permanent, irrigation ditches, and drainage ditches) in tillable areas of Chubut Province, Argentina. This report represents the first record of Cx. eduardoi from this Province and extends its range to latitude 45°S. Immature stages of Cx. eduardoi were found in 8 out of 109 (7.3 %) freshwater habitats and were significantly more prevalent in semi-permanent water bodies. Positive sites had significantly larger surface areas and more vegetation cover than negative sites.

Ação promotora do berílio em catalisadores da síntese do estireno

The catalytic dehydrogenation of ethylbenzene in presence of steam is the main commercial route to produce styrene. The industrial catalysts are potassium- and chromia-doped hematite which show low surface areas leading to bad performance and short life. In order to develop catalysts with high areas, the effect of beryllium on the textural properties and on the catalytic performance of this iron oxide was studied. The influence of the amount of the dopant, the starting material and the calcination temperature were also studied. In sample preparations, iron and beryllium salts (nitrate or sulfate) were hydrolyzed with ammonia and then calcinated. The experiments followed a factorial design with two variables in two levels (Fe/Be= 3 and 7; calcination temperature= 500 and 700ºC). Solids without any dopant were also prepared. Samples were characterized by elemental analysis, infrared spectroscopy, surface area and porosity measurements, X-ray diffraction, DSC and TG. The catalysts were tested in a microreactor at 524ºC and 1 atm, by using a mole ratio of steam/ ethylbenzene=10. The selectivity was measured by monitoring styrene, benzene and toluene formation. It was found that the effect of beryllium on the characteristics of hematite and on its catalytic performance depends on the starting material and on the amount of dopant. Surface areas increased due to the dopant as well as the nature of the precursor; samples produced by beryllium sulfate showed higher areas. Beryllium-doped solids showed a higher catalytic activity when compared to pure hematite, but no significant influence of the anion of starting material was noted. It can be concluded that beryllium acts as both textural and structural promoter. Samples with Fe/Be= 3, heated at 500ºC, lead to the highest conversion and were the most selective. However, catalysts prepared from beryllium sulfate are the most promising to ethylbenzene dehydrogenation due to their high surface area which could lead to a longer life.

Análise por difração de raios x de filmes de óxidos cerâmicos compostos por IrO2/TiO2/CeO2

Independent of the sample form (powder or film), XRD analysis of Ir0,3Ti(0,7-x)Ce xO2, (nominal) mixtures, for x=0, shows the formation of a solid solution phase between IrO2 and TiO2, as well as the rutile phases of IrO2 and TiO2. The presence of the anatase phase of TiO2 is also confirmed. The introduction of 30 mol% CeO2 in the mixture reveals the presence of the CeO2 and Ce2O3 phases, besides the already mentioned ones, in the powder. In the film form, however, an amorphous phase is identified. When all of the TiO2 is substituded by CeO2, for both sample forms, the only phases found are IrO2, CeO2 and Ce2O3. This result suggests cerium oxides are not capable of forming solid solutions with either IrO2 or (Ir,Ti)O2 acting solely as a dispersant matrix for these phases. These results are consistent with the much higher electrochemically active surface area when CeO2 is introduced in the binary Ti/Ir0,3Ti0,7O2 mixture. It was possible to establish a relationship between the electrochemical stability of the supported films and their crystalline structure. The unexpected presence of TiO2 and Ti2O3 in the Ti/Ir0,3Ce0,7O2 (film sample) is attributed to oxidation of the Ti support during the calcination step.

Reação de geração de oxigênio em eletrodos de Mn2O3 suportados em aço inoxidável

A study of the kinetics of oxygen evolution in alkaline conditions from ceramic films of Mn2O3 supported on stainless steel was carried out. This study has been done through the determination of transfer coefficients, Tafel slopes and exchange currents using potentiodynamic and quasi-potentiostatic measurements. The activation energy was determined as a function of the overpotential and, additionally, the electrode active surface was estimated. The results are consistent with data already published for other electrodes, implying that the methods used in this work were reliable and precise.

Nanoparticle-coated organic-inorganic microparticles: experimental design and gastrointestinal tolerance evaluation

The influences of the spray-drying parameters and the type of nanoparticles (nanocapsules or nanospheres) on the characteristics of nanoparticle-coated diclofenac-loaded microparticles were investigated by using a factorial design 3². Gastrointestinal tolerance following oral administration in rats was evaluated. Formulations were selected considering the best yields, the best encapsulation efficiencies and the lowest water contents, presenting surfaces completely coated by nanostructures and a decrease in the surface areas in relation to the uncoated core. In vitro drug release demonstrated the influence of the nanoparticle-coating on the dissolution profiles of diclofenac. Nanocapsule-coated microparticles presented a protective effect on the gastrointestinal mucosa.

25 anos de quimiometria no Brasil

Chemometric activities in Brazil are described according to three phases: before the existence of microcomputers in the 1970s, through the initial stages of microcomputer use in the 1980s and during the years of extensive microcomputer applications of the ´90s and into this century. Pioneering activities in both the university and industry are emphasized. Active research areas in chemometrics are cited including experimental design, pattern recognition and classification, curve resolution for complex systems and multivariate calibration. New trends in chemometrics, especially higher order methods for treating data, are emphasized.

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.

Preparação de carvão ativado em baixas temperaturas de carbonização a partir de rejeitos de café: utilização de FeCl3 como agente ativante

Ferric chloride as a new activating agent was used to obtain activated carbons from agroindustrial waste. This material was prepared at three temperatures of pyrolysis, 200, 280 and 400 ºC. The carbonaceous materials obtained after the activation processes showed high specific surface areas (BET), with values higher than 900 m² g-1. The materials showed different behaviors in the adsorption of methylene blue dye and reactive red textile dye in water solutions. An important fact in the use of FeCl3 as an activating agent is that the activation temperature is at 280 ºC, well below of those commonly employed in chemical or physical activations described in the literature.