Calcium tungstate (CaWO4) crystals were prepared by microwave-assisted hydrothermal (MAH) and polymeric precursor methods (PPM). These crystals were structurally characterized by X-ray diffraction (XRD), N2 adsorption, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. The morphology and size of these crystals were observed by field emission scanning electron microscopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-Vis) absorption and photoluminescence (PL) measurements. Moreover, these materials were employed as catalysts towards gas phase toluene oxidation reaction. XRD indicates the purity of materials for both preparation methods and MAH process produced crystalline powders synthesized at lower temperatures and shorter processing time compared to the ones prepared by PPM. FE-SEM images showed particles with rounded morphology and particles in clusters dumbbells-like shaped. PL spectra exhibit a broad band covering the visible electromagnetic spectrum in the range of 360 to 750 nm. XANES and EXAFS results show that preparation method does not introduce high disorders into the structure, however the H2-TPR results indicated that the catalyst reducibility is affected by the preparation method of the samples.

Two mesoporous SBA-15 materials with different morphologies (spherical and fiber-shaped) were synthesized and evaluated as supports for nickel-based catalysts for polymerization reactions. The supports were pretreated with trimethylaluminum (TMA), and the catalyst dibromo-bis(4-amino-2,3,5,6-tetramethylimino)acenaphthene nickel(II) was attached to the supports and activated with TMA or MAO (methylaluminoxane). Characterization showed that the insertion of cetyltrimethylammonium bromide (CTABr) as a cosurfactant led to spherical SBA-15 with a decrease in particle and pore sizes to 4.8 nm compared to 6.5 nm in traditional fiber-shaped SBA-15. The spherical SBA-15 showed thicker walls than the fiber-shaped SBA-15, attributed to the increase in functional groups of the cosurfactant. The different spherical and fiber-shaped morphologies did not show any significant difference in the productivity of polyethylene. The catalyst supported on spherical SBA-15 materials showed 58% productivity compared to its homogeneous analogue using TMA as a cocatalyst.

Benzene, toluene and xylene (BTX) are a particular class of volatile organic compounds, which are highly toxic pollutants. In this study, samples of gallium-containing mesoporous silica (MS-Ga7% and MS-Ga11%) were synthesized and their catalytic activity in the oxidation of BTX was investigated. The physicochemical characterization shows that the inclusion of gallium in the mesoporous silica structure leads to an increase in the number of oxygen vacancies in the structure of the MS-Ga system, which can result in an increase in the total and surface oxygen mobility. The results show the highest conversion for benzene (65%), with > 40% for toluene and > 28% for o-xylene. The high catalytic activity observed was attributed to a combination of several factors including a higher number of active sites (gallium and gallium oxide) being exposed, with a greater mobility of the active oxygen species on the surface of the catalyst promoting the catalytic activity.

Neste estudo foi preparado um catalisador à base de WO3 para investigar a atividade catalítica na oxidação total de compostos orgânicos voláteis conhecidos como benzeno, tolueno e xileno (BTX). Para uma faixa de temperaturas baixas (50-450 ºC) os únicos produtos de reação foram CO2 e H2O. Os resultados de caracterização para o catalisador sugerem que a elevada atividade catalítica pode ser atribuída aos efeitos de interação forte do metal, o que é possivelmente originada a partir da pequena diferença entre o parâmetro de rede e os planos (111), (020) e (002), assim como a presença de espécies W4+, W5+ e W6+ sobre a superfície do catalisador, que reagem com espécies de oxigênio ativo.

In this study we prepared a WO3-based catalyst to investigate its catalytic activity in the total oxidation of the volatile organic compounds known as benzene, toluene and xylene (BTX). For a range of low temperatures (50-450ºC) the only reaction products were CO2 and H2O. The results for the catalyst characterization suggested that the high catalytic activity could be attributed to the effects of a strong metal interaction, which is possibly originated from the small lattice parameter difference between the (111), (020) and (002) lattice planes and the presence of W4+, W5+ and W6+ species on the surface of the catalyst which react with active oxygen species.

O objetivo deste estudo foi reduzir a emissão de compostos orgânicos como BTX (benzeno, tolueno e xilenos), devido à sua toxicidade e efeitos adversos ao meio ambiente. Neste sentido, os catalisadores (SiO2(1-x)Cu x) foram desenvolvidos para apresentar elevada atividade catalítica na conversão de BTX em CO2 e H2O sem a necessidade do uso de solventes e materiais prejudiciais ao meio ambiente, com baixo custo de produção e excelente reprodutibilidade. O Cu foi impregnado (2,99; 5,01; 10,01 e 19,97%) em suportes (SiO2) por impregnação úmida a partir de nitrato de cobre(II). O estudo foi realizado na faixa de temperatura de 50-350 ºC. Os catalisadores descritos nesse artigo apresentam elevada atividade catalítica na oxidação total de BTX. A conversão de benzeno neste estudo excedeu 85% a 150 ºC.

The aim of this study was to reduce the emissions of organic compounds, such as BTX (benzene, toluene and xylenes), due to their toxicity and adverse effects on the environment. In this regard, catalysts (SiO2(1-x)Cu x) were developed which exhibit high catalytic activity for converting BTX compounds to CO2 and H2O, and which do not require the use of solvents and materials detrimental to the environment, with low production cost and good reproducibility. Cu (from copper(II) nitrate) was loaded (2.99; 5.01; 10.01 and 19.97 wt.%) onto supports (SiO2) by wet impregnation. The study was carried out within the temperature range of 50-350 ºC. The catalysts described in this paper have high catalytic activity in the total oxidation of BTX. The conversion of benzene in this study exceeded 85% at 150 ºC.