RESUMO
Herein, we present a new type of high-performance catalyst for aerobic oxidation of organosulfur compounds based on tungsten carbide. The synthesis of tungsten carbide was performed via microwave irradiation of the precursors, which makes it possible to obtain a catalyst in just 15 min. The synthesized catalyst was investigated by a variety of physicochemical methods: X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, electron microscopy, and N2 adsorption/desorption. It was shown that active centers containing tungsten in the transition oxidation state (+4) play a key role in the activation of oxygen. The main factors influencing the conversion of dibenzothiophene (DBT) were investigated. It should be noted that 100% conversion of DBT can be achieved under relatively mild conditions: 120 °C, 3 h, 6 bar, and 0.5% wt catalyst. The catalyst retained its activity for at least six oxidation/regeneration cycles. The simplicity and speed of synthesis of the proposed catalyst in combination with its high activity and stability open broad prospects for its further use both for oxidative desulfurization and for other reactions of aerobic oxidation of organic substrates.
RESUMO
In this work, new heterogeneous Mo-containing catalysts based on sulfonic titanium dioxide were developed for the oxidation of sulfur-containing model feed. The synergistic effect of molybdenum and sulfonic group modifiers allows for enhancing catalytic activity in dibenzothiophene oxidative transformation, and a strong interaction between support and active component for thus obtained catalysts provides increased stability for leaching. For the selected optimal conditions, the Mo/TiO2-SO3H catalyst exhibited 100% DBT conversion for 10 min (1 wt % catalyst, molar ratio of H2O2:DBT, 2:1; 80 °C). Complete oxidation of DBT in the presence of the synthesized catalyst is achieved when using a stoichiometric amount of oxidizing agent, which indicates its high selectivity. The enhanced stability for metal leaching was proved in recycling tests, where the catalyst was operated for seven oxidation cycles without regeneration with retainable activity in DBT-containing model feed oxidation with hydrogen peroxide under mild reaction conditions. In 30 min of the reaction (H2O2:S = 2:1 (mol), 0.5% catalyst, 5 mL of acetonitrile, 80 °C), it was possible to reduce the content of sulfur compounds in the diesel fraction by 88% (from 5600 to 600 ppm).
RESUMO
We have studied for the first time the role of hydrophobicity of the mesoporous silicate SBA-15 on the activity and the service life of a catalyst in the peroxide oxidation of sulfur-containing compounds. Immobilization of the molybdate anion on the SBA-15 support via ionic bonding with triethylammonium groups allows us not only to decrease the reaction temperature to a relatively low value of 60 °C without a drop in the dibenzothiophene conversion degree but also to increase the service life of the catalyst to many times that of the known analogs. The support and catalyst structures were investigated by low-temperature nitrogen adsorption/desorption, Fourier-transform infrared spectroscopy, X-ray fluorescence analysis, and transmission electron microscopy. Immobilization of the molybdate anion on the SBA-15 support, modified with ammonium species, prevents the leaching of active sites. However, only alkyl-substituted ammonium species minimize DBT sulfone adsorption, which significantly increases the catalyst's service life. The synthesized catalyst Mo/Et3N-SBA-15 with hydrophobic properties is not sensitive to the initial sulfur content and hydrogen peroxide amount and retains its activity for at least six cycles of oxidation without regeneration. These catalysts can be efficiently used for clean fuel production.
