Deicy Barrera

Non-hydrothermal Synthesis of Cylindrical Mesoporous Materials: Influence of the Surfactant/Silica Molar Ratio

Ordered mesoporous materials of MCM-41 and SBA-15 type were synthesized under non-hydrothermal conditions using different molar ratios of surfactant/silica, ranging from 0.07 to 0.27 for MCM-41 and from 0.009 to 0.021 for SBA-15. Nitrogen adsorption/desorption isotherms at 77 K were used to evaluate the specific surface areas, with values up to 1450 m2/g and 1100 m2/g being obtained for MCM-41 and SBA-15, respectively. Scanning electron microscopy was carried out to study the morphology of the materials. The sizes of the primary mesopores and the pore thicknesses were assessed by a geometrical method using X-ray diffraction and nitrogen adsorption data. The results for the pore sizes were compared with those obtained by a recently reported method (VBS-method) and the Non-Local Density Functional Theory (NLDFT) model, both proposed to evaluate the pore-size distribution of these materials. It was found that, under the synthesis conditions, the surfactant/silica molar ratio had an important effect on the final characteristics of these materials.

Surface modified mesoporous nanocast carbon as a catalyst for aqueous sulfide oxidation and adsorption of the produced polysulfides

In this work, a mesoporous nanocast carbon prepared using SBA-15 as a template was modified by surface oxidation to produce unique catalysts for sulfide oxidation/elimination from an aqueous medium. Different characterization techniques (BET, SEM, Raman, FTIR, potentiometric titration, elemental analyses, cyclic voltammetry) showed that treatment with concentrated HNO3 at 80 °C for 5, 15 and 30 min attacks the carbon structure creating different oxygen surface functionalities in concentrations varying from 0.4–1.1 mmol g−1 with a small effect on the surface area (1080–1148 m2 g−1) and pore volumes (micropore 0.17–0.20 cm3 g−1 and mesopores 0.36–0.50 cm3 g−1). These materials showed high activities for the oxidation of sulfide in an aqueous medium forming polysulfides, e.g., S22−, S32− and S42−, which are rapidly eliminated from the aqueous medium. These results are discussed regarding efficient sulfide oxidation at redox surface oxygen sites leading to the formation of higher polysulfides followed by adsorption of these relatively large and more hydrophobic molecules into the mesopores.

Natural and Modified Montmorillonite Clays as Catalysts for Synthesis of Biolubricants

In this study, natural and modified clays were evaluated as catalysts in an esterification reaction to obtain bio-based lubricants. The biolubricants are environmentally preferred to petroleum-based lubricants because they are biodegradable and non-toxic. Other advantages include very low volatility due to the high molecular weight and excellent viscosity properties with temperature variations. Modifications in natural clay were performed intending to obtain materials with different textural properties that could improve the reaction under study. The modified clays were obtained in two ways: by pillarization using Al13 Keggin polyoxocations or by acid treatments with H2SO4, HCl and HNO3. All samples were evaluated for the esterification reaction of fatty acids from castor oil (FACO) using 2-ethyl-hexanol. During the reaction step, a zeolite-based adsorbent was used for water removal to increase the reaction equilibrium conversion. Gas chromatography and nuclear magnetic resonance were performed to ensure the formation of the products. The highest conversion of fatty acids to esters was obtained using pillared clays. Adding adsorbent in the reaction medium (10 g of 3A zeolite to 100 g of FACO), the conversion improved from 74–88 wt % after 6 h at 50 °C.