100 resultados para Síntese química
Resumo:
In recent years, studies about the physicochemical properties of mixed oxides, call attention of the scientific community, properties like as piezoelectricity, photoluminescence, or applications as catalysts, arise in these compounds, when their chemical compositions are modified, in this context some routes are employed in the synthesis of these materials, among which can be cited these methods: ceramic, combustion, co-precipitation, Pechini or polymeric precursor method, hydrothermal, sol-gel; these routes are divided into traditional routes or chemical routes. In this work were synthesized oxides with variable composition, from the thermal decomposition of titanium, cobalt, nickel and praseodymium nitrilotriacetates. The nitrilotriacetates were characterized by IR Spectroscopy (FTIR), Thermogravimetric (TG/ DTG) and Differential Scanning Calorimetry (DSC), while oxides have been characterized by X-ray diffraction (XRD), Spectrofluorimetry and IR Spectroscopy (FTIR). From FTIR data, it was demonstrated that the displacement of the band corresponding to the carboxylate group (νCOOH) at 1712 cm-1, present in nitrilotriacetic acid (H3NTA), for 1680-1545 cm-1, these stretches are characteristics of coordinated nitrilotriacetates, By thermal analysis (TG/DTG /DSC), it was suggested, that in an oxidizing atmosphere (air) oxides are obtained at lower temperatures than in an inert atmosphere N2(g). By results from X-ray Diffraction (XRD), it was determinated that the oxides are crystalline and the predominant phases obtained are summarized titanate phases rutile and ilmenite. By fluorimetry was observed that the intensity of emission bands are directly proportional to the concentration of ions Ni2+, Co2+ and Pr3+, and IR spectroscopy (FTIR) from oxides, demonstrated the disappearance of characteristic bands by nitrilotriacetates, determining the complete decomposition of the nitrilotriacetates in oxides
Resumo:
The cultivation of microalgae biomass in order to produce biodiesel arises as an extremely promising aspect, in that the microalgae culture includes short cycle of reproduction, smaller areas for planting and residual biomass rich in protein content. The present dissertation evaluates the performance and features, through spectrometry in the region of infrared with transformed Fourier (FTIR) and spectrometry in the region of UVvisible (UV-Vis), of the extracted lipid material (LM) using different techniques of cell wall disruption (mechanical agitation at low and at high spin and agitation associated with cavitation). The technique of gas chromatography (GC) brought to light the success of alkaline transesterification in the conversion of oil into methyl monoesters (MME), which was also analyzed by spectroscopic techniques (FTIR, proton magnetic resonance (1H NMR) and carbon (13C NMR). Through thermogravimetric analysis (TGA) were analyzed the lipid material (LM), biodiesel and the microalgae biomass. The method which provided the best results concerning the efficiency in extraction of the LP of Monoraphidium sp. (12,51%) was by mechanical agitation at high spin (14 000 rpm), for 2 hours being the ideal time, as shown by the t test. The spectroscopic techniques (1H NMR, 13C NMR and FTIR) confirmed that the structure of methyl monoesters and the chromatographic data (CG) revealed a high content of saturated fatty acid esters (about 70%) being the major constituent eicosanoic acid (33,7%), which justifies the high thermal stability of microalgae biodiesel. The TGA also ratified the conversion rate (96%) of LM into MME, pointing out the quantitative results compatible with the values obtained through GC (about 98%) and confirmed the efficiency of the extraction methods used, showing that may be a good technique to confirm the extraction of these materials. The content of LM microalgae obtained (12,51%) indicates good potential for using such material as a raw material for biodiesel production, when compared to oil content which can be obtained from traditional oil for this use, since the productivity of microalgae per hectare is much larger and requires an extremely reduced period to renew its cultivation
Resumo:
The synthesis of MFI-type zeolite membranes was carried by the process in situ or hydrothermal crystallization. We studied the homogenization time of the room temperature and gel filtration just before the crystallization step performed out in an oven, thus obtaining a more uniform zeolite film. The powder synthesized zeolite (structure type MFI, Silicalite) was characterized by several complementary techniques such as Xray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, temperature programmed desorption (TPD), Fourier Transform infrared spectroscopy (FTIR) and textural analysis by nitrogen adsorption (specific surface area). For the purpose of evaluating the quality of the layer supported on the ceramic support, N2 permeation tests were carried starting from room temperature to 600 °C, where values were observed values more appropriate permeation from 200 °C. With the data obtained, it was made into a graph of temperature versus permeation function, the curve of surface diffusion was found. For scanning electron microscopy, we observed the formation of homogeneous crystals and the zeolite film showed no fissures or cracks, indicating that the process of synthesis and subsequent treatments not damaged the zeolite layer on the support. Carried permeation studies were found values ranging from 3.64x10-6 to 3.78x10-6, 4.71x10-6 to 5.02x10-6, to pressures 20 and 25 psi, respectively. And the mixture xylenes/N2 values were between 5.39x10-6 to 5.67x10-6 and 8.13x10-6 to 8.36x10-6, also for pressures of 20 and 25 psi. The values found for the separation factor were 15.22 at 400 °C in the first experiment and 1.64 for the second experiment at a temperature of 150 °C. It is concluded that the Silicalite membrane was successfully synthesized and that it is effective in the separation of binary mixtures of xylenes
Resumo:
This work involved the synthesis, characterization and proposing the molecular structure of coordination compounds involving ligands pyrazine-2-carboxamide (PZA) and 4- hydrazide acidic pyridine carboxylic (INH) and metals of the first transition series (M = Co2+, Ni2+ and Cu2+). For the characterization of the compounds used were analytical techniques such as infrared absorption spectroscopy average (FT-IR) molar conductivity measurements, CHN elemental analysis, EDTA Complexometric, measurement of melting point, X-ray diffraction by powder method, Thermogravimetry (TG) and Differential Thermal Analysis (DTA) and Simultaneous Differential Scanning Calorimetry (DSC). The absorption spectra in the infrared region suggested that the ligand coordination to the metal center occurs through the carbonyl oxygen atom and nitrogen alpha pyrazine ring to those complexes formed with PZA. For INH complexes with metal-ligand coordination is through the carbonyl oxygen and nitrogen of the terminal hydrazide grouping. The conductivity measurements of the complexes in aqueous solution they suggest to all behavior of the type 1:2 electrolytes, and conduct of non-electrolytes in acetonitrile. The results obtained by CHN elemental analysis and EDTA Complexometric allowed to infer the stoichiometry of the compounds synthesized. For all of the complexes obtained was possible to record the melting points, neither of which melted near the melting temperature of the free ligands. The X-ray diffraction showed that the complexes of pyrazinamide exhibited diffraction lines, suggesting that these compounds are crystalline, while compounds of isoniazid, with the exception of cobalt, exhibited diffraction lines, indicating that they are crystalline. The results from the TG-DTA and DSC allowed information regarding the dehydration and thermal decomposition of these complexes
Resumo:
The nanostructured molecular sieve SBA-15 was synthesized by the hydrothermal method, and modified with lanthanum with Si/La molar ratios of 25, 50, 75 and 100. The materials were evaluated as catalysts for the cracking of n-hexane model reaction. Type SBA- 15 and LaSBA-15 mesoporous materials were synthesized using tetraetilortosilicato as a source of silica, hydrochloric acid, heptahydrate lanthanum chloride and distilled water. Pluronic P123 triblock. polymer was used as structure template. The syntheses were carried out by 72 hours. The obtained SBA-15 samples were previously analyzed by thermogravimetry, in order to check the conditions of calcination for removal of organic template. Then, the calcined materials were characterized by X-ray diffraction, infrared spectroscopy, adsorption and desorption of nitrogen, scanning electron microscopy and X-ray microanalysis by dispersive energy. The acidity of the samples was determined using adsorption of n-bulinamina and desorption followed by thermogravimetry. It was found that the hydrothermal synthesis method was suitable for the synthesis of the SBA-15 mesoporous materials, with an excellent degree of hexagonal ordering. The reactions of catalytic cracking of n-hexane were carried out using a fixed bed continuous flow microreactor, coupled on-line to a gas chromatograph. From the catalytic evaluation, it was observed that the mesoporous materials containing lanthanum showed different results for the reaction of cracking of nhexane compared to the unmodified mesoporous material SBA-15. As a result of cracking was obtained as main products hydrocarbons in the range of C1 to C5. The catalyst that showed better properties in relation to the acidity and catalytic activity was LaSBA-15 with the ratio Si/La = 50
Resumo:
Different compositions of Ni0,5-xCuxZn0,5Fe2O4 and Ni0,5-xCoxZn0,5Fe2O4 0 ≤ x ≤ 0.3 were synthesized ferrite y the citrate precursor method. The stoichiometric compositions were calcined in air at 350°C and then pressed into pellets and toroids. The pressed samples were sintered at temperatures of 1000, 1050 and 1100°C/3h in air control at the speed of heating and cooling. The calcined powders were characterized by XRD, TGA / DTG, FTIR, SEM and vibrating sample magnetometry (VSM) and the sintered samples by XRD, SEM, MAV, density and measurements of permeability and magnetic losses. There was pure phase formation ferrimagnetism applied at all temperatures except for A-I composition at all sintering temperatures and A-II only at a temperature of 1100°C. Crystallite sizes were obtained by Rietveld analysis, nanometer size from 11 to 20 nm for the calcined powders. For SEM, the sintered samples showed grain size between 1 and 10 micrometers. Bulk density (ρ) of sintered material presented to the Families almost linear behavior with increasing temperature and a tendency to decrease with increasing concentration of copper, different behavior of the B Family, where the increase in temperature decreased the density. The magnetic measurements revealed the powder characteristics of a soft ferrimagnetic material. Two processes of magnetization were considered, the superparamagnetism at low temperatures (350°C) and the formation of magnetic domains at higher temperatures. Obtaining the best parameters for P and B-II magnetic ferrites at high temperatures. The sintered material at 1000°C showed a relative permeability (μ) from 50 to 800 for the A Family and from 10 to 600 for the B Family. The samples sintered at 1100°C, B Family showed a variation from 10 to 1000 and the magnetic loss (tan δ) of A and B Families, around of 1. The frequency response of the toroidal core is in the range of 0.3 kHz. Several factors contribute to the behavior of microstructure considering the quantities μ and tan δ, such as the grain size, inter-and intragranular porosity, amount of grain boundary and the aspects of the dynamics of domain walls at high frequencies.
Resumo:
Oxygen carriers are metal oxides which have the ability to oxidize and reduce easily by various cycles. Due to this property these materials are widely usedin Chemical-Looping Reforming processes to produce H2 and syngas. In this work supports based on MCM-41 and La-SiO2 were synthesized by hydrothermal method. After the synthesis step they were calcined at 550°C for 2 hours and characterized by TG, XRD, surface area using the BET method and FTIR spectroscopy. The deposition of active phase, in this case Nickel, took place in the proportions of 5, 10 and 20% by weight of metallic nickel, for use as oxygen carriers.The XRD showed that increasing in the content of Ni supported on MCM-41 resulted in a decrease in spatial structure and lattice parameter of the material. The adsorption and desorption curves of the MCM-41 samples exhibited variations with the increase of Ni deposited. Surface area, average pore diameter and wall density of silica showed significant changes , due to the increase of the active phase on the mesoporous material. By other hand, in the samples with La-SiO2 composition was not observed peaks characteristic of hexagonal structure, in the XRD diffractogram. The adsorption/desorption isotherms of nitrogen observed are type IV, characteristic of mesoporous materials. The catalytic test indicates that the supports have no influence in the process, but the nickel concentration is very important, because the results for minor concentration of nickel are not good. The ratio H2/O2 was close to 2, for all 15 cycles involving the test storage capacity of O2, indicating that the materials are effective for oxygen transport
Resumo:
Orthoferrites AFeO3 (A = rare earth) are an important class of perovskite oxides that exhibit weak ferromagnetism. These materials find numerous applications as chemical sensors, cathodes for fuel cells and catalysis, which make them interesting from the standpoint of science and technology. Their structural, electrical and magnetic properties are dependent on many factors such as the preparation method, heat treatment conditions, chemical composition and replacement of cations in sites A and/or B. In this paper, LaFe1-xMnxO3 (0 ≤ x ≤ 1) orthoferrites-type was prepared by Pechini method and Microwave-assisted combustion reaction in order to evaluate the influence of synthesis route on the formation of oxide, as well as the effect of parcial replacement of iron by manganese and heat treatment on the magnetic properties. The precursor powders were calcined at 700°C, 900°C, 1100°C and 1300°C for 4 hours and they were characterized by the techniques: Thermogravimetric analysis (TGA), X ray diffraction (XRD), Refinement by Rietveld method, Scanning electron microscopy (SEM), Reduction temperature programmed (RTP) and Magnetic hysteresis measurements performed at room temperature. According to the XRD patterns, the formation of perovskite phase with orthorhombic structure was observed for the systems where 0 ≤ x ≤ 0.5 and rhombohedral for x = 1. The results also showed a decrease of lattice parameters with the parcial replacement of iron by manganese and consequently a reduction in cell volume. The hysteresis curves exhibited weak ferromagnetism for the systems prepared by both synthesis methods. However, a dependence of magnetization as a function of dopant content was observed for samples produced by Pechini method. As for the systems prepared by combustion reaction, it was found that the secondary phases exert a strong influence on the magnetic behavior
Resumo:
Three studies were performed using tailings kaolin for the synthesis of zeolite A. The first synthesis of zeolite A was performed using a kaolin waste generated from the beneficiation of kaolin for paper production process was studied. The kaolin waste was thermally activated at a temperature range of 550-800°C. For comparison was performed a synthesis pattern of Zeolite A(procedure IZA). The prepared materials were characterized by 27Al MAS NMR, X-ray diffraction and scanning electron microscopy with microprobe rays. The pre-tramento proved to be the most appropriate and suitable temperatures are between 600 and 700°C. Observed the formation of zeolite A in all materials, reaching 52% crystallinity, and the presence of phase sodalite and amorphous material. The second study was the use of a highly reactive metakaolin originating from the Jari region in the synthesis of zeolite A by a new method of hydrothermal synthesis. The zeolite is obtained pure and highly crystalline employing the Jari kaolin calcined at 600 ° C for 2h when the transformation to metakaolin occurs. Get to zeolite phase A at 4pm. The best crystallization time was of 24 h afforded a crystallinity of 67.9%. The third study was the evaluation of the NaOH / metakaolin and crystallization time on the synthesis of zeolite NaA from a sample of kaolin waste, named Kaolin Coverage. The experiments were performed using statistical design (axial points) and rejoinder the center point. The samples were characterized by X-ray diffraction (XRD), scanning microscopic analysis and chemical analysis using an EPMA microprobe. The results showed that a relationship exists between the amount of NaOH added and the crystallization time. The experiment performed using the lowest ratio NaOH / metakaolin (0.5) and shorter (4 h) produced an amorphous material. The increase ratio of NaOH / metakaolin and crystallization time leads to formation of a more crystalline NaA phase, but the presence of phase with sodalite as impurities
Resumo:
Enzymatic synthesis of peptides using proteases has attracted a great deal of attention in recent years. One key challenge in peptide synthesis is to find supports for protease immobilization capable of working in aqueous medium at high performance, producing watersoluble oligopeptides. At present, few reports have been described using this strategy. Therefore, the aim of this thesis was to immobilize proteases applying different methods (Immobilization by covalent bound, entrapment onto polymeric gels of PVA and immobilization on glycidil metacrylate magnetic nanoparticles) in order to produce water-soluble oligopeptides derived from lysine. Three different proteases were used: trypsin, α-chymotrypsin and bromelain. According to immobilization strategies associated to the type of protease employed, trypsin-resin systems showed the best performance in terms of hydrolytic activity and oligopeptides synthesis. Hydrolytic activities of the free and immobilized enzymes were determined spectrophotometrically based on the absorbance change at 660 nm at 25 °C (Casein method). Calculations of oligolysine yield and average degree of polymerization (DPavg) were monitored by 1H-NMR analysis. Trypsin was covalently immobilized onto four different resins (Amberzyme, Eupergit C, Eupergit CM and Grace 192). Maximum yield of bound protein was 92 mg/g, 82 mg/g and 60 mg/g support for each resin respectively. The effectiveness of these systems (Trypsin-resins) was evaluated by hydrolysis of casein and synthesis of water-soluble oligolysine. Most systems were capable of catalyzing oligopeptide synthesis in aqueous medium, albeit at different efficiencies, namely: 40, 37 and 35% for Amberzyme, Eupergit C and Eupergit CM, respectively, in comparison with free enzyme. These systems produced oligomers in only 1 hour with DPavg higher than free enzyme. Among these systems, the Eupergit C-Trypsin system showed greater efficiency than others in terms of hydrolytic activity and thermal stability. However, this did not occur for oligolysine synthesis. Trypsin-Amberzyme proved to be more successful in oligopeptide synthesis, and exhibited excellent reusability, since it retained 90% of its initial hydrolytic and synthetic activity after 7 reuses. Trypsin hydrophobic interactions with Amberzyme support are responsible for protecting against strong enzyme conformational changes in the medium. In addition, the high concentration of oxirane groups on the surface promoted multi-covalent linking and, consequently, prevented the immobilized enzyme from leaching. The aforementioned results suggest that immobilized Trypsin on the supports evaluated can be efficiently used for oligopeptides synthesis in aqueous media
Resumo:
This work reports the synthesis of zeolites with different compositions (pure silica, Si/Ti and Si/Al), via hydroxide and fluoride medium using the cation 1-butyl-3- methylimidazolium as structure directing agent. Initially, the cation was synthesized in chloride form and used for the synthesis in hydroxide medium. An anion-exchange (Cl- for OH-) was required for the synthesis in fluoride medium. Different reactants were used for the formation of gels synthesis, resulting in the crystallization of MFI and TON phases, the latter predominant in many compositions. The cation and synthesized zeolites obtained were characterized by different techniques such as NMR, TG/DTG, XRD, SEM, N2 adsorption and desorption, DRS and EPMA. Besides characterizing the cation and zeolites, the mother liquor of hydroxide synthesis was characterized and it was possible to observe a modification of the cation in the synthesis conditions employed. The materials synthesized in this work can be applied in catalytic reactions and adsorption
Resumo:
Two pillaring methods were tested to synthesize pillared clays containing mixed Al/Co pillars. Using the first method, based on the traditional procedure, were obtained materials containing different Co concentrations: 10, 25, 50, 75 and 100 % of Co in the pillaring solution. Just the experiments with low concentrations (10 and 25 % of Co) has formed pillared clays, whereas the sample with 25 % of cobalt showed best results compared with the one obtained just using Al as pillaring agent (basal spacing higher than 18 Å and surface area bigger than 300 m²/g). The 27Al NMR results pointed out the formation of mixed Al/Co pillars due to decreased between the intensities of AlVI/AlIV signals, indicating that the AlIV content decreased while Co content increased, suggesting the isomorphic substitution of Al atoms for Co in the Keggin ion structure (pillaring agent). For the samples containing 75 and 100 % of cobalt, it was verified the formation of others materials, which could be identified as hydrotalcite like compounds. The second pillarization method was named mixed layers, because the objective was to intercalate clay layers with hydrotalcite layers. Thus, after calcination, the hydrotalcite layers would dehydroxylate, resulting just in the metals oxides, intercalated between the clay sheets, thus generating, a pillared clay. For this purpose, were tested 4 synthesis procedures: physical mixture, mixture in water, ionic exchange under reflux and in situ synthesis. Of these, the method which showed the best results was the in situ synthesis, in which basal spacings of 14 Å (after calcination) were obtained, indicating that the samples are intercalated with metal oxides (Mg and Al). This procedure was reproduced with a Co-Al LDH (layered double hydroxide) and similar results were obtained, testifying the method reproducibility
Resumo:
In this study five compositions were synthesized zirconia doped with cerium and neodymium ions in the system Ce10-xNdx Zr90O2 with 0,5 ≤ x ≤ 4,0 using the Pechini method. The powders were characterized by thermogravimetric analysis, differential thermal analysis, infrared spectroscopy and X-ray diffraction, with application of Rietveld refinement of the calcination temperatures of 350ºC/3h and 30 minutes at 900ºC/3h. All compositions stabilized with a mixture of cubic and tetragonal phase zirconia. The samples were pressed into bars and sintered at 1500°C/3h and 1500°C/6h, being characterized by Xray diffraction, with application of the Rietveld refinement, density and porosity using Archimedes method, scanning electron microscopy and resistance the three point bending. It has been observed the increase in strength with increasing sintering temperature for the compositions x = 2,0 and x = 4,0. For x = 2,0 the main phase was the cubic with 92,56% with crystallite size of 0,56 μm, density and porosity of 96,82% from 1,36%. For x = 4,0 was a mixture of cubic and tetragonal phase with 21% and 37,98%, respectively. The crystallite size was 54,21 nm and 49,64 nm with a density porosity of 97,45% and 1,32% respectively. In the analysis of the fracture surface was observed a greater amount of grain fracture intragranular type, which contribute to increase the mechanical strength of the ceramic. Increased addition of the neodymium ion in the crystal lattice of the zirconium showed a nearly linear behavior with increasing mechanical strength of the zirconia ceramic. Was obtained a bending resistance of 537 ± 38 MPa for the composition x = 2,0 predominantly attributed to cubic phase with 92,56%
Resumo:
To overcome the challenge of meeting growing energy demand in a sustainable way, biodiesel has shown very promising as alternative energy can replace fossil fuels, even partially. Industrially, the biodiesel is produced by homogeneous transesterification reaction of vegetable oils in the presence of basic species used as catalysts. However, this process is the need for purification of the esters obtained and the removal of glycerin formed after the reaction. This context, the alternative catalysts have that can improve the process of biodiesel production, aiming to reduce costs and facilitate its production. In this study, the AlSBA-15 support with Si / Al ratio = 50 was synthesized, as like as the heterogeneous catalysts of zinc oxide and magnesium supported on mesoporous AlSBA-15 silica, in the concentrations of 5, 10, 15 and 30 %, relative to the support. The textural properties and structural characterization of catalysts and supports were determined by techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) coupled to the chemical analyzer, adsorption / desorption of N2, thermal analysis (TG / DTG), absorption spectroscopy in the infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Characterization results indicated that the support AlSBA-15 retained the hexagonal ordered after the incorporation of zinc oxide and magnesium oxide in the holder. For heterogeneous catalysts, ZnO-AlSBA-15, that was observed the presence of zinc oxide nanoparticles dispersed in the surface and interior channels of the mesoporous and microporous support. The catalytic activity was evaluated by the transesterification reaction of sunflower oil via methylic route, and some reaction parameters were optimized with the most active catalyst in biodiesel production by sunflower oil. For the series of heterogeneous catalysts, the sample with 30 % ZnO supported on AlSBA-15 showed a better conversion of triglyceride to methyl esters, about 95.41 % of reaction conditions: temperature 175 °C, with molar ratio of 42:1, stirring at 200 rpm and under a pressure of 14 bar for 6 h. The catalyst MgO-AlSBA-15 showed no catalytic activity in the studied reactions
Resumo:
The Layered Double Hydroxides has become extremely promising materials due to its range of applications, easily obtained in the laboratory and reusability after calcination, so the knowledge regarding their properties is of utmost importance. In this study were synthesized layered double hydroxides of two systems, Mg-Al and Zn-Al, and such materials were analyzed with X-ray diffraction and, from these data, we determined the volume density, planar atomic density, size crystallite, lattice parameters, interplanar spacing and interlayer space available. Such materials were also subjected to thermogravimetric analysis reasons for heating 5, 10, 20 and 25 ° C / min to determine kinetic parameters for the formation of metaphases HTD and HTB based on theoretical models Ozawa, Flynn-Wall Starink and Model Free Kinetics. In addition, the layered double hydroxides synthesized in this working ratios were calcined heating 2.5 ° C / min and 20 ° C / min, and tested for adsorption of nitrate anion in aqueous solution batch system at time intervals 5 min, 15 min, 30 min, 1h, 2h and 4h. Such calcined materials were also subjected to exposure to the atmosphere and at intervals of 1 week, 2 weeks and 1 month were analyzed by infrared spectroscopy to study the kinetics of regeneration determining structural called "memory effect"