Patterson P. Souza

Nanostructured vanadium-doped iron oxide: catalytic oxidation of methylene blue dye

V-doped iron oxides are used as heterogeneous catalysts to oxidize the dye methylene blue in an aqueous medium containing hydrogen peroxide. XRD and Mossbauer spectroscopy reveal that vanadium is incorporated into the iron oxide structure. The H2O2 pretreatment of the solid catalyst promotes important surface and structural changes in the iron oxides primarily due to the formation of peroxo-vanadium complexes, which specifically enhance the catalytic properties of the material. Transmission electron microscope images show that the H2O2 treatment also tends to decrease the mean particle size of the material grains. V-doped iron oxides were found to play an important role as solid catalysts in H2O2 reactions. The prepared vanadium containing iron oxide was confirmed to exhibit remarkable catalytic activity for the oxidation of methylene blue, an important contaminant from textile industry. In fact, the ESI-MS spectrum obtained for methylene blue after reaction with the V-doped oxide shows hydroxylation by hydroxyl radicals in solution forming species with m/z = 130 and m/z = 110.

Modified Niobium Oxyhydroxide Catalyst: An Acetalization Reaction to Produce Bio-additives for Sustainable Use of Waste Glycerol

We report the synthesis and characterization of new niobium oxyhydroxide catalysts from ammonium niobium oxalate (NH4[NbO(C2O4)2(H2O)](H2O)n) or niobium chloride (NbCl5) precursors. The materials have been modified by incorporating a surfactant, specifically cetyltrimethylammonium bromide, on the catalyst surface to impart partial hydrophobicity to the catalyst. The change in the precursor during the synthesis changes properties associated with the morphology, texture and number of acid sites. These properties provide increased contact at the interface between the hydrophilic and hydrophobic regions to improve the catalytic properties, particularly in biphasic reactions. Acetalization reactions were tested using three different glycerols: commercial glycerol p.a., a crude residual originating from biodiesel production and the same material after desalination. The results show 65 and 60 % conversion for the acetalization under mild reactions conditions.

The combined effect between Co and carbon nanostructures grown on cordierite monoliths for the removal of organic contaminants from the liquid phase

Carbon nanostructures were grown on the surface of cordierite monoliths using Fe or Co nanoparticles by catalytic chemical vapor deposition (CCVD) using ethanol in order to intensify the interaction of this support with organic contaminants. The materials produced were extensively characterized by X-ray diffraction, thermal analysis, elemental analysis, atomic absorption spectrometry, Raman spectroscopy and scanning and transmission electron microscopies. These materials were tested in the removal of quinoline and methylene blue from liquid solutions. Promising results were attributed to the combined effect of the hydrophobic carbon nanostructures in adsorbing the organic contaminants with cobalt metal cores that are able to promote the oxidation of the adsorbed molecules via a heterogeneous Fenton process.

Fe/C and FeMo/C hybrid materials for the biphasic oxidation of fuel contaminants

In the present work, hybrid magnetic nanoparticles based on Fe and FeMo coated with carbon nanostructures (Fe/C and FeMo/C) were produced by catalytic chemical vapor deposition at different temperatures using ethanol as the carbon source. Scanning electron microscopy, thermal analysis, Raman spectroscopy, X-ray diffraction, and Mossbauer spectroscopy analyses suggested that hematite was reduced by ethanol at 700 and 900 °C, producing carbon nanostructures such as nanofibers and nanotubes. The Fe/C and FeMo/C hybrid composites showed remarkable magnetic and amphiphilic properties. The composites were successfully used to oxidize sulfur and nitrogen contaminants present in fuels in a biphasic system.

Synthetic Niobium Oxyhydroxide as a Bifunctional Catalyst for Production of Ethers and Allyl Alcohol from Waste Glycerol

A synthetic niobia was modified by treatment with hydrogen peroxide to be used as a catalyst for converting glycerol into petrochemical compounds. The catalytic properties of niobium oxyhydroxide were obtained by generating acidic and oxygenated groups (peroxo groups) on the solid surface. Compounds like ethers and allyl alcohol were obtained. A very active H2O2-modified catalyst showed high activity for the oxidation and dehydration of 91% of glycerol conversion using H2O2 and 46% of allyl alcohol selectivity in volatile phase. The product was analyzed by gas chromatography-mass spectrometry (GC-MS), thermogravimetry-mass spectrometry (TGA-MS) and nuclear magnetic ressonance (NMR). These results strongly suggest that the reactions involve acid and oxidizing species generated after the reaction of niobium with H2O2. H and C multidimensional NMR spectroscopy confirmed the results obtained with GC-MS and showed the production of several compounds after niobia treatment.

Generating active and non-selective oxidizing species by previous treatment of niobium-doped mesoporous silica with hydrogen peroxide

Active catalysts for oxidation of non-selective organic compounds were produced by doping silica with niobium followed by treatment of Nb-doped mesoporous silica with hydrogen peroxide. Low angle XRD patterns revealed that niobium replaced silicon in the silica framework. TEM images confirmed the isomorphic substitution as indicated by the increase of the interplanar spacing after incorporation with Nb in the silica framework. The H2O2 treatment strongly affected the morphology of Nb-doped silica, but EDS and XPS measurements showed that the niobium is maintained in the silica structure even after H2O2 treatment. The isomorphic substitution of Si4+ by Nb5+ in the silica framework can generate acidic sites on the Nb-doped silica, which can contribute to the electron transfer in the oxidation process of organic compounds. Catalytic tests using rhodamine B as a model molecule of textile effluents showed that both processes of Nb doping and treatment with H2O2 are essential to obtain a highly active and oxidizing system. The better performance of Nb-doped silica treated with H2O2 was assigned to formation of niobium-peroxo groups, which act as excellent oxidizing sites.