Ping Mei

Mesoporous titania–silica–polyoxometalate nanocomposite materials for catalytic oxidation desulfurization of fuel oil

A series of mesoporous titania–silica–polyoxometalate (HPW–TiO2–SiO2) nanocomposite materials with different silica–titania ratios were prepared in the presence of non-ionic surfactant by evaporation induced self-assembly method. XRD, TEM, nitrogen adsorption–desorption isotherm and FTIR measurements indicated these materials possess mesoporous structure with relatively uniform channel-like pores and large internal BET surface areas. The incorporated polyoxometalate clusters preserve intact their Keggin structure into the mesoporous frameworks. The nanocomposites were used as catalysts for oxidative desulfurization of model fuel, which was composed of dibenzothiophene (DBT) and hydrocarbon, while H2O2 is used as oxidant. The catalytic oxidation results show that the catalysts are very active in refractory bulky molecule organosulfur compounds in fuel oil. The mesoporous HPW–TiO2–SiO2 also shows high selectivity for DBT oxidation in the presence of benzene and achieved the goal of desulfurization. The surface acid strength and acidic sites were characterized by NH3–TPD and Py-FT-IR. It revealed that Lewis acidic sites play an important role in the removal of organic sulfur compounds from the DBT–petroleum ether–benzene system. After regeneration of used catalysts three times, the activity of catalysts has not obviously decreased.

Self-assembled HPW/silica–alumina mesoporous nanocomposite as catalysts for oxidative desulfurization of fuel oil

Mesoporous silica–alumina–polyoxometalate (HPW/SiO2–Al2O3) nanocomposite materials with silica–aluminum molar ratios of 10–80 have been successfully synthesized by evaporation induced self-assembly method with non-ionic surfactant P123 as template agent. The surface areas and pore sizes of the obtained HPW/SiO2–Al2O3 materials are in the range of 509–623xa0m2xa0g−1 and 3.6–3.8xa0nm, respectively, with different silica–aluminum molar ratios. The incorporated polyoxometalate clusters preserve their intact Keggin structure into the mesoporous frameworks. The Py–FTIR investigations indicate that the surface acidity of catalysts gradually increases with an increase in the percentage of aluminium, and the Lewis acidity sites are predominant. The nanocomposites were used as catalysts, and H2O2 as oxidant for oxidative desulfurization (ODS) of model fuel, which was composed of benzothiophene (BT), petroleum ether and benzene. The results show that the adsorption capacity and ODS performance of catalysts have close relationship with their surface acidity. An appropriate amount of Lewis acidity sites can contribute to the selective oxidation of the BT due to the preferential adsorption of BT on the catalyst surface, while the Brönsted acidity sites have a negative impact on the selective oxidation of the BT. As a result, the mesoporous HPW/SiO2–Al2O3 with silica–aluminum molar ratio of 50 shows the highest selectivity for BT oxidation in the presence of benzene and has achieved the goal of desulfurization. In addition, the catalyst shows excellent reusing ability, which makes it a promising catalyst in ODS process.

The adsorption of dibenzothiophene using activated carbon loaded with cerium

Cerium-loaded activated carbon was prepared by classical soaking impregnation method and tested for dibenzothiophene adsorption from model fuels. The new adsorbents showed much better adsorption capacity and selectivity towards DBT than the virgin carbon. The adsorbents were characterized by N2 adsorption, Boehm titration and FTIR. The improved performance is mainly due to changes in surface chemistry. The results show that the performance of activated carbon as desulfurization adsorbents can be considerably enhanced by a simple cerium loading method.

Synthesis and Characterization of a ZrO2/AC Composite as a Novel Adsorbent for Dibenzothiophene

Zirconium dioxide was impregnated into a commercial activated carbon (AC) by hydrothermal treatment employing an aqueous ZrOCl2•8H2O solution. The ZrO2/AC composites thus prepared were tested as adsorbents for dibenzothiophene (DBT) from a model diesel fuel. In comparison to the pure AC, impregnation of ZrO2 was found to lead to a ca. 17% increase in the adsorption capacity. The optimal ZrO2 loading and hydrothermal pH were determined as 0.1 mmol/g and 7, respectively. The spent adsorbents were regenerated by toluene washing, with the ZrO2/AC composite exhibiting a higher adsorptive capacity than pure AC even after three such recycles. The ZrO2/AC composite was also characterized by the physical adsorption of nitrogen and Boehm titrations. The results indicated that surface acidic sites on the impregnated ZrO2 may play an important role in the improved desulphurization performance of the composite.

Synthesis and Performance of Mesoporous Phosphotungstic Acid/Alumina Composite as a Novel Oxidative Desulfurization Catalyst

A series of mesoporous phosphotungstic acid/alumina composites (HPW/Al2O3) with various HPW contents were synthesized by evaporation-induced self-assembly method. These composites were characterized by nitrogen adsorption-desorption, TEM, FTIR, and UV-vis, and were tested as catalysts in oxidation desulfurization of model fuel composed of dibenzothiophene (DBT) and hydrocarbon, using H2O2 as the oxidant. These composites exhibited high activity in catalytic oxidation of DBT in model fuel and good reusing ability. The best performance was achieved by using the mesoporous HPW/Al2O3 with 15wt% HPW content, which resulted in a DBT conversion of 98% after 2 h reaction at 343 K, and it did not show significant activity degradation after 3 recycles. Characterization results showed that the mesoporous structure of alumina and the Keggin structure of HPW were preserved in the formed composite. These results suggested that HPW/Al2O3 could be a promising catalyst in oxidative desulfurization process.

Synthesis of mesoporous silica-zirconia supported phosphotungstic acid and its catalytic performance for oxidative desulfurization of fuel

Mesoporous silica-zirconia supported phosphotungstic acid was synthesized by evaporation induced self-assembly method and used as oxidative desulfurization catalysts. The structural properties of as-prepared catalysts were characterized using various analytical techniques including X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and nitrogen adsorption desorption. The experimental results showed that HPW was highly dispersed on mesoporous framework. The surface acidity of catalysts was analyzed by FTIR measurement of adsorbed pyridine.The surface Lewis acidity was improved with increasing the content of zirconium in the samples. The mesoporous composites were used as catalysts with H2O2 as oxidant for oxidative desulfurization of model fuel. The catalytic activity results showed that the surface Lewis acid sites acted as selective adsorption active sites for dibenzothiophene, which facilitated the sulfur removal from model fuel in the presence of arene. A slight decrease in activity of the recovered catalyst used in the proceeding rounds indicated the reusability of the catalyst.

Photocatalytic Degradation of Rhodamine B over Sulfated SiO2-TiO2 Composite by Sulphuric Acid Impregnation Method

Abstract Sulfate modified SiO2-TiO2 photocatalysts with different SO42− loadings were prepared by incipient-wetness impregnation method using H2SO4 solution with various concentrations. The as-prepared SO42−/SiO2-TiO2 samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer- Emmett-Teller (BET) method, Uv-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and terephthalic acid photoluminescence probing technique (TA-PL), respectively. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic degradation of rhodamine B under ultraviolet light irradiation. The effects of H2SO4 solution concentration on the structure, morphology, surface properties and photocatalytic activity of SO42−/SiO2-TiO2 samples were investigated. The results indicated that the catalyst prepared with 4 mol/L H2SO4 solution, it showed the highest photocatalytic activity. The higher photocatalytic activity could be attributed to the improved surface properties and the enhanced separation rate of photoinduced electron-hole pairs.