Abstract Selective photocatalytic oxidation of benzyl alcohol to benzaldehyde and reduction of nitrobenzene to aniline reactions are investigated by using SiO2@TiO2 spheres produced in a simple route using chitosan as a template. The spheres are predominantly macroporous and, the XRD points out an amorphous crystallographic profile suggesting the uniform distribution of TiO2. Under low-power lighting for 4 hours, the conversions achieved was of the order of 49% and 99% for benzyl alcohol and nitrobenzene, respectively, with selectivity to benzaldehyde and aniline of 99% in both reactions. The study also follows the effects of the solvent and the presence of O2.

This work presents the results obtained for the gas chromatography-mass spectrometry (GC-MS) monitoring of the liquid-phase hydrodeoxygenation (HDO) reaction of furfural (FFR) to 2-methylfuran (MF) over a bifunctional Ru/RuOx/C catalyst in the presence of a direct source of H2. Hydrogenation and hydrogenolysis reactions of FFR and of the intermediate furfuryl alcohol (FA), respectively, were independently studied to provide insights on the HDO mechanism. The mass spectra monitoring of the kinetic isotope effect indicated the HDO reaction occurs through a two-step mechanism comprising of an initial ruthenium-mediated hydrogenation reaction of FFR to FA. In the second step, the FA thus formed experiences a hydrogenolysis reaction via ring activation where the hydrogen atoms are firstly attached to the C3 carbon generating a ring activated structure and removing the OH group. The observation of the peaks at m/z 85 and 84 in the mass spectrum of the MF product confirms this reaction pathway.

Abstract Silica spheres coated with titania (SiO2@TiO2) were synthesized using chitosan as template. The N2 adsorption/desorption isotherms of the spheres point to meso and macroporous characteristics and the elemental mapping by EDS shows uniform distribution of Ti on the surface of the silica spheres, leading to formation of an amorphous structure (XRD). The results from the model reaction of photocatalytic degradation of methylene blue (MB) show a good stability of the spheres regarding their reuse. The tests with various additives pointed to hydroxyl radical production as the main via of MB degradation. The photocatalytic activity of the spheres in the hydroxylation of benzene to form phenol, hydroquinone and benzoquinone was assessed. The kinetic data point to the formation of phenol as the limiting step; in addition, the phenol consumption occurs by parallel and consecutive reactions producing benzoquinone.

Mesoporous mixed copper-aluminum oxides and copper-silicon oxides were synthesized with polymeric precursors route in order to evaluate the effect of the support acidity on the catalytic stability due to the carbon deposit and the copper surface characteristics on the catalytic activity for the gas-phase conversion of glycerol to acetol. The samples were characterized by different techniques such as inductively coupled plasma (ICP), thermogravimetry and differential thermal analyses (TGA-DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption isotherms, temperature-programmed reduction with H2 (H2-TPR) and microcalorimetry of NH3 adsorption. The metallic copper surface was shown by XPS, which was observed an increase with the copper loading without marked changes between Si or Al support using the same copper content. The Cu-Al catalysts present acidic properties close to that of the pure alumina support while the Cu-Si solid is not acid, as expected. Reduced catalysts were evaluated in the reaction of glycerol conversion. The catalytic results showed a clear dependence of the glycerol conversion to acetol with the Cu metal surface and the initial catalytic properties did not depend on the support acidity, since the copper is the major active site. It was observed 95% of acetol selectivity and 80% of glycerol conversion for the best catalyst. However, the support acidity influenced the catalyst stability, since Cu-Al solid deactivated continuously by contrast to Cu-Si sample, which reached stability after 2 h of reaction. The higher acidity for the Al support leads to a greater carbon deposit compared to Si support, blocking the active sites and providing a rapid catalytic deactivation.

Polymeric precursor method and wet impregnation route were applied to synthesize copper and aluminium-based catalysts in order to obtain a material with interesting properties in catalytic reactions. The changes in the structural, morphological and textural properties due to the choice of preparation method were characterized by different techniques, such as XRD, N2 physisorption isotherms and SEM. The XRD results of the solids present the formation of γ-Al2O3 or CuO and β-Al(OH)3, depending on the preparation method. The average crystallite diameters of the alumina were estimated by the Scherrer's formula with a particle size of 5.2 nm. N2 physisorption isotherms analysis shows that the alumina is a mesoporous material with a high specific surface area. An excessive increase in surface area was observed after Cu2+ insertion by wet impregnation from β-Al(OH)3 support, which is explained by the redissolution and recrystallization of bayerite to γ-Al2O3 during the impregnation of Cu2+ and recalcination process, respectively. The SEM images confirmed this phenomenon. Catalytic tests explain that the combination of the two methods improves the activity, selectivity and the stability in the conversion of glycerol to acetol. The results indicate that the way of catalyst preparation affects its structural, textural and morphological properties and consequently the catalytic performance

Solid samples containing a Ca2Fe2O5 phase were synthesized using the Pechini method. The samples were characterized using X-ray diffraction, thermogravimetric analysis, differential thermal analysis, X-ray fluorescence, nitrogen adsorption/desorption isotherms, and scanning electron microscopy. The stability of the Ca2Fe2O5 phase was evaluated in the photocatalytic degradation of methylene blue (MB) in aqueous solution in the presence of bubbling gas (air, N2, or CO2). The presence of CO2 is known to suppress MB degradation. After the photocatalytic test, changes were observed in the crystalline phase of all systems. These results suggest the low stability of the Ca2Fe2O5 phase in aqueous systems and the significant effect of CO2 on the photocatalytic activity of the Ca2Fe2O5 phase.

Materials containing aluminum and iron oxide were synthesized through the preparation of hybrid spheres and tested in the dehydrogenation of ethylbenzene in the presence of CO2. The catalytic results suggest that the high initial ethylbenzene conversion is due to the contribution of basic sites. These results also point to a competitive process between CO2 adsorption and the oxidative dehydrogenation of ethylbenzene for the basic sites (lattice oxygen). In spite of the coke deposition is originating from ethylbenzene and CO2, the amount of carbonaceous deposits was smaller with the presence of CO2, if compared with the dehydrogenation in the absence of CO2.

Neste trabalho é apresentada a reação de condensação aldólica entre metanol e acetona promovida por nanopartículas de dióxido de estanho, não dopadas e dopadas com as terras raras Ce e Y. Diversas condições de relação molar metanol/acetona foram avaliadas, objetivando a obtenção com elevada seletividade do composto a, b-insaturado, metil vinil cetona. As nanopartículas foram preparadas empregando-se o método dos precursores poliméricos. As amostras foram caracterizadas por meio de adsorção de N2 para determinação de área superficial específica (BET), difração de raios X (DRX), adsorção química de CO2, espectroscopia de fotoelétrons (XPS) e microscopia eletrônica de transmissão (MET). O comportamento catalítico observado para as amostras de SnO2 sugere que a relação molar metanol/acetona e a dopagem com as terras raras desempenham um papel importante na atividade catalítica do material e na seletividade aos produtos reacionais. Os resultados de DRX e XPS apontam para a formação de uma camada de segregação, para as amostras dopadas, devido ao tratamento térmico imposto. Essa camada de segregação afeta diretamente o comportamento catalítico do material frente à reação de condensação.

Aldol condensation between methanol and acetone, catalyzed by undoped and rare earths (Ce and Y) doped tin oxide nanoparticles is presented. Several methanol/acetone molar ratio conditions were evaluated aiming to produce methyl vinyl ketone as the main product. The undoped and doped ultrafine nanoparticles of tin oxide were prepared using the polymeric precursor method. The characterization was carried out by means of N2 adsorption (BET), X-ray diffraction (XRD), CO2 chemisorption, X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM). The catalytic behavior observed for SnO2 samples suggests that the methanol/acetone molar ratio and Ce and Y doping play an important role in the catalytic activity and in the product selectivity. The results from XRD and XPS pointed to the de-mixing process for the doped samples, due to the heat-treatment. This segregation layer contributes to the observed change in the catalytic behavior.

Ca1-xLa xTiO3 powders were prepared by the polymeric precursor method. X-ray diffraction (XRD), FT-Raman spectroscopy, transmission electron microscopy (TEM), and N2 and CO2 adsorption were used for the microstructural and surface characterization of the powders. Room temperature photoluminescence (PL) was observed in Ca1-xLa xTiO3 amorphous particles. The PL intensity of these powders was found to be dependent on the lanthanum molar concentration.

The carbon dioxide reforming of methane was carried out over nickel catalysts supported on the gamma-Al2O3/CeO2 system prepared by wet impregnation. With the increase of the CeO2 weight in the catalyst, a higher stability was observed in the catalytic activity, together with an excellent resistance to carbon deposition and a better Ni dispersion. The catalysts were characterized by means of surface area measurements, TPR, H2 chemisorption, XRD, SEM, EDX, XPS and TEM. An interaction between Ni and CeO2 was observed to the Ni/CeO2 sample after activation in a H2 atmosphere above 300 ºC. Such behavior has a significantly influence on the catalytic activity.

Zeolite catalysts have been extensively used in petroleum refining and the chemical industry although they are deactivated by coke deposition. In order to find the best condition to avoid deactivation, the coke formation on H-mordenite was studied in this work. The coke was produced during benzene transalkylation with C9+ aromatics, under several reaction conditions. It was found that hydrogenated coke was produced in all samples without affecting the selectivity of toluene and xylene formation. This is explained in terms of the mordenite structure and the presence of hydrogen.

Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the beta-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

Capsules were prepared from chitosan (QTS)-poly(vinyl alcohol) (PVA) blend by saline coacervation and then by formalization. A adsorbent based on chitosan, insoluble on acid solution, was obtained. The morphology, average diameters of QTS/PVA capsules and their pores were studied by using scanning electron microscopy. The entrapment-adsorption of dimethylglioxime and ethylenediaminetetracetate by the capsules were studied. The removal of the ion nickel (II) and copper (II), was more effective than by using unloaded capsules.