Synthesis, Characterization, and Catalytic Properties of Ti, V, and Zr-HMS Prepared by Metallocene Grafting

Ti, V, and Zr-HMS molecular sieves were prepared by grafting the respective metallocene onto the pure silica HMS, XRD, N₂-physisorption, TEM, UV-Vis spectroscopy and elemental analysis were performed to characterize the samples prepared. The XRD patterns of the metal-grafted samples exhibited well-defined (100) reflections, and the intensity remained almost constant as with pure silica HMS. Surface area, hysteresis loop in N₂ adsorption isotherms and N₂ volume adsorbed decreased after metal grafting. The order of catalytic activity for 2,6-di-tert-butylphenol (2,6-DTBP) oxidation using H₂O₂ was V-HMS (91.5 % conversion) Ti-HMS(20.3 %) Zr-HMS(8.4 %). Metal leaching was detected for all the grafted samples in the reaction media; V-HMS(22 wt.%) Zr-HMS(3 wt.%) > Ti-HMS(2 wt.%). For V-HMS and Zr-HMS, further reaction after catalyst filtration indicated significant contribution to the reaction by the dissolved species.     

Immobilization of phosphotungstic acid in an amino‐containing metal–organic framework for oxidative desulfurization

A composite material has been successfully synthesized using an amino‐containing metal–organic framework (NH₂‐MOF) and phosphotungstic acid (PTA). This composite was characterized using X‐ray diffraction, high‐resolution transmission electron microscopy, nitrogen adsorption–desorption measurements, Fourier transform infrared spectroscopy and X‐ray fluorescence. Characterization results confirmed the immobilization and good distribution of PTA in the NH₂‐MOF. The PTA/NH₂‐MOF was subsequently applied in the oxidative desulfurization of dibenzothiophene (DBT) with H₂O₂ as the oxidant in n‐octane under atmospheric conditions. Under optimal reaction conditions, the oxidative desulfurization conversion of DBT reached 100%, and there was no significant decrease of the catalytic activity after four recycles. Kinetic experiments were also performed for the reaction at various temperatures, which indicated that oxidative reaction rates followed pseudo first‐order kinetics, and the apparent activation energy for the desulfurization reaction was 34.1 kJ mol^?1. The results indicated that this material exhibited excellent catalytic performance for oxidative desulfurization of DBT. Copyright © 2016 John Wiley & Sons, Ltd.     

Macroporous 3D carbon-nitrogen (CN) confined MoOx catalyst for enhanced oxidative desulfurization of dibenzothiophene

Macroporous 3D carbon doped with nitrogen confined Mo catalyst (MoO_x@CN) had been prepared by a facile one-step pyrolysis technique using silica as a template and was employed for oxidative desulfurization (ODS) of dibenzothiophene (DBT) in model fuel with H₂O₂ as oxidant. The effect of different operating conditions (i.e., reaction temperature and time, catalyst dosage, H₂O₂/DBT (O/S) molar ratio) were also systematic investigated. Under the optimal reaction condition, MoO_x@CN catalyst exhibited highly excellent ODS performance toward DBT, the highest sulfur removal efficiency can be up to 99.9% and sulfur content was wiped out from 800 ppm to 10 ppm. Due to the robust 3D structure promoting rapid transfer, in addition to the increased number of active sites induced by the Mo vacancies, the catalyst, prepared using chitosan and ammonium heptamolybdate in a mass ratio of 1:0.5, displayed rapid kinetics and low activation energy in the oxidation of dibenzothiophene. Moreover, it exhibited excellent recyclability after five cycles without any obvious decrease in catalytic activity for the oxidative desulfurization reaction.     

Preparation, characterization, and catalytic performance of a novel methyl-rich Ti-HMS mesoporous molecular sieve with high hydrophobicity

A novel methyl-rich Ti-containing hexagonal mesoporous silica (Ti-HMS) molecular sieve with high hydrophobicity has been prepared by a two-step method involving co-condensation followed by vapor-phase methyl grafting. The sample was characterized by XRD, N₂ adsorption, FTIR, UV-visible and ²⁹Si NMR spectroscopies, TG, ICP-AES, and hydrophilicity measurements, and its catalytic performance was evaluated using the epoxidation of cyclohexene as a probe reaction. The Ti-HMS material retains a typical mesoporous structure and compared with a co-condensed Ti-HMS prepared in a one-step method possesses more methyl groups and higher hydrophobicity, and also exhibits better catalytic activity and selectivity.     

Characterization and catalytic performance of methyl-grafted Ti-HMS catalysts prepared by the CVD method

Methyl-grafted Ti-HMS catalysts were prepared by the chemical vapor deposition (CVD) method using TiCl₄ as titanium source and various organic silanes as silylating agents. The catalysts were characterized by XRD, N₂-adsorption-desorption, FTIR, ²⁹Si NMR, TGA, DR UV-vis, and evaluated by the epoxidation of propylene using cumene hydroperoxide (CHP) as oxidant. The results reveal that the silylated Ti-HMS catalysts are more active than the unsilylated Ti-HMS catalyst, and the methyl-grafted Ti-HMS catalyst silylated with hexamethyldisilazane (HMDSZ) exhibits better epoxidation performance than the analogues silylated with trimethylchlorosilane (TMCS) or dimethyldichorosilane (DMDCS). It is proposed that not only the form of T-O-SiMe_n (n = 2 or 3) but also the breakage of Ti-O-T (Si-O-Si or Si-O-Ti) are observed in silylation using Cl-containing silylating agents (TMCS or DMDCS), which decrease the hydrophobicity of Ti-HMS catalysts and destroy the tetracoordinated titanium species that responsible for the epoxidation performance. This phenomenon has not been observed in silylation with HMDSZ.     

Oxidative desulfurization of thiophene derivatives with H<Subscript>2</Subscript>O<Subscript>2</Subscript> in the presence of catalysts based on MoO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> under mild conditions

The catalysts based on MoO₃/Al₂O₃ were synthesized and tested using aqueous hydrogen peroxide as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO₃–WO₃)/Al₂O₃ prepared by a conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT, which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexadecyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reaction efficiently.     

Removal of dibenzothiophene in diesel oil by oxidation over a promoted activated carbon catalyst

Oxidative removal of dibenzothiophene (DBT) in n-octane solution by H₂O₂ on a promoted activated carbon (AC) catalyst was studied. DBT adsorption and catalytic behaviors on AC were examined. Effects of pH in aqueous phase, amounts of AC and formic acid (HCOOH) for promotion as well as initial molar H₂O₂/S ratio were investigated. Experimental results led to conclusion that DBT was readily oxidized by H₂O₂ over an AC catalyst promoted by HCOOH. Suitable amount of AC can improve the activity of H₂O₂ resulting in a deeper extent of sulfur removal. A 100% conversion of DBT in an octane solution by H₂O₂ oxidation was attained on the HCOOH-H₂O₂/AC catalyst at 80°C for a reaction time of 30 min.     

镍助剂对碳化钼催化剂的二苯并噻吩加氢脱硫性能的影响

 将MoO3和Ni-Mo混合氧化物在CH4/H2气氛中程序升温还原碳化制备了相应的碳化钼和碳化镍钼催化剂, X射线粉末衍射表征其物相分别为β-Mo2C和Ni-Mo2C. 考察了Ni助剂对碳化钼催化剂的制备及二苯并噻吩加氢脱硫反应性能的影响. 结果表明, Ni助剂的加入降低了碳化钼催化剂所需的还原碳化温度,提高了催化剂的比表面积,并对其二苯并噻吩加氢脱硫反应活性有明显的促进作用. Ni助剂添加量以Ni/Mo原子比为0.3为宜,此时Ni和Mo之间的催化协同效应达到最佳. 当反应压力为3.0 MPa, 反应温度为330 ℃, 空速8 h-1, H2/原料液体积比为500∶1时, 625 ℃还原碳化制备的碳化镍钼催化剂对0.6%二苯并噻吩/环己烷溶液的二苯并噻吩转化率达到96.25%, 较相应的碳化钼催化剂提高了1.57倍.     

Aqueous ethylation of organotin compounds in simple solution for speciation analysis by cryofocussing and detection by atomic absorption spectrometry — comparison with hydride generation

A 2³ factorial experimental design has been used to determine the optimum reaction conditions for organotin ethylation in simple aqueous solutions for speciation by Cryogenic Trapping/ Gas Chromatography/Atomic Absorption Spectrometry (CT/GC/AAS). The factors chosen and their levels of variation (? and +) were the pH of the solution (levels 3 and 5), the amount of NaBEt₄ added (levels 1 and 9 mg) to the organotins and the time of ethylation reaction (levels 10 and 20 min). Optimum conditions were investigated for monomethyltin (MMT), diethyltin (DET) and dibutyltin (DBT) in mixed solution at a concentration of 10 ng of each Sn compound in 50 ml of solution (200 ng·l^?1). The influence of the different factors on the yield of the ethylation reaction in the ranges investigated depends on the degree of substitution and the nature of the alkyl groups of the organotins. The ethylation reaction for DET and DBT is more efficient at high pH levels, MMT gives higher yields at lower pH. Both MMT and DET require a high amount of reagent, while reagent concentration has no real influence on the DBT signal. Comparison of hydride generation and ethylation as derivatisation procedures for organotin speciation has been performed in simple solutions. Under these analytical conditions, hydride generation is shown to be slightly more sensitive than ethylation by a factor of 1.4 for MMT and DET and 2 for DBT. However derivatisation using ethylation provides more reproducible results and is not affected by inorganic interferents.     

PMAA microgel surface-supported phase transfer catalyst as reusable microreactors for ultra-deep desulfurization

The reusable microreactors, poly(methacrylic acid) (PMAA) microgels surfacely covered with 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (AEM) and K₂{W(=O)(O₂)₂(H₂O)}₂ (W2) complexes, have been synthesized by using an ion exchange reaction between AEM located on PMAA microgels and W2 in aqueous solution. The final composite microspheres and intermediate products are characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectrophotometer, and thermogravimetric analysis, respectively. The results indicated the PMAA/AEM/W2 composite microspheres with surface-wrinkling morphology and core-shell structure. The feasibility of the composite microspheres used as reusable microreactors in catalytic oxidation of dibenzothiophene (DBT) was investigated. Additionally, the effects of some factors, including the amount of the microreactors, temperature, H₂O₂/DBT molar ratio, the loaded amount of AEM, DBT concentration, and recycling times, on the catalytic oxidation were examined. The results demonstrated that the prepared composite microspheres possess high catalytic performance and reusability in the catalytic oxidation of DBT.     

活性炭负载TiO2光催化氧化二苯并噻吩的研究

以活性炭负载的TiO2为光催化剂,H2O2为氧化剂,30W紫外灯为光源,对含二苯并噻吩（DBT）的模型硫化物进行光催化氧化脱硫研究。考察了TiO2的煅烧温度、负载量、催化剂用量、H2O2用量和光照时间对DBT去除率的影响。实验结果表明,用溶胶 凝胶法制备的TiO2 /活性炭催化剂对DBT具有很好的光催化效果。最佳反应条件为,催化剂煅烧温度400℃,TiO2的负载量为32％,催化剂用量0.7g/100mL, H2O2最佳用量为10mL,即O/S（摩尔比）为14。在最佳反应条件下,光照时间8h,DBT去除率为90％, 此反应为一级动力学反应。     

Selective oxidation of organic sulfides by mononuclear and dinuclear peroxotungsten(VI) complexes

Clean conversion of a variety of sulfides and dibenzothiophene (DBT) to the corresponding sulfoxide or sulfone could be achieved in high yields at room temperature using mononuclear as well as dinuclear diperoxo complexes of tungsten as oxidants, by a variation of reaction conditions. The compounds could also effectively catalyze oxidation of sulfides by H₂O₂ to selectively yield sulfone with reasonably good turnover frequency (TOF).     

An organic‐inorganic heterogeneous catalyst based on Keplerate polyoxometalates for oxidation of dibenzothiophene derivatives with Hydrogen peroxide

An organic‐inorganic material (NH₄)₂(MimAM)₄₀[Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂] have been synthesized by reacting [(NH₄)₄₂[Mo^VI₇₂ Mo^V₆₀O₃₇₂(CH₃COO)₃₀(H₂O)₇₂] with the ionic liquid 3‐Aminoethyl‐1‐methylimidazolium bromide. The catalyst showed remarkably a high catalytic performance in the oxidation of dibenzothiophene (DBT) derivatives with H₂O₂ 35% as a safe and green oxidant. The main parameters affecting the process including catalyst, acid additive, hydrogen peroxide amounts and temperature have been investigated in detail. Sulfur removal of DBT in n‐heptane reached to 98.3% yield at 40 °C using 2.5 mmol H₂O₂ and 100 mg of (NH₄)₂(MimAM)₄₀[Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂] after 90 min. Under the optimal conditions, BT (benzothiophene), DBT (dibenzothiophene) and 4,6‐DMDBT (4,6‐dimethyl‐dibenzothiophene) achieved high desulfurization efficiency. Our results showed that the reactivity order of different model sulfur compounds are thiophene <4,6‐dimethyl dibenzothiophene< dibenzothiophene. The catalysts could be easily separated from the reaction solution by simple filtration and recycled for several times without loss of activity.     

Water-soluble polymer anchored peroxotitanates as environmentally clean and recyclable catalysts for mild and selective oxidation of sulfides with H2O2 in water

Anchoring of peroxotitanium (pTi) species to linear water-soluble acrylic acid based polymers, poly(sodium acrylate) (PA) and poly(sodium methacrylate) (PMA) led to the successful synthesis of a pair of new, water-tolerant and recyclable catalysts of the type [Ti₂(O₂)₂O₂(OH)₂]^4-—L (L = PA or PMA), highly effective in chemoselective sulfoxidation of organic sulfides with 30% H₂O₂ in aqueous medium at ambient temperature. The catalytic protocol is high yielding (TOF up to 11,280 h^?1), operationally simple as well as environmentally clean and safe, being free from halide, or any other toxic auxiliaries. The catalysts are sufficiently stable to afford easy recyclability for at least 10 consecutive reaction cycles of sulfoxidation with consistent activity selectivity profile. Oxidation of dibenzothiophene (DBT) to respective high purity sulfoxide or sulfone could also be accomplished using the same catalysts by variation of reaction conditions.     

Controllable preparation of highly dispersed TiO2 nanoparticles for enhanced catalytic oxidation of dibenzothiophene in fuels

The aggregation of nanoparticle catalysts is one of the main problems in catalytic reactions. In this study, a series of TiO₂ nanoparticle catalysts with various dispersions were prepared and applied in the catalytic oxidation of dibenzothiophene (DBT) systems. Compositions and structures of the as‐prepared samples were analyzed by means of wide‐angle X‐ray diffraction, Raman and X‐ray photoelectron spectroscopies. The dispersions of TiO₂ nanoparticles were controlled by calcining at various temperatures and verified using transmission electron microscopy. It was found that the activities of TiO₂ nanoparticles in the catalytic oxidation of DBT were positively correlated with the dispersions. TiO₂ nanoparticles calcined at 500 °C (500‐TiO₂) showed the best catalytic activity and the oxidation of DBT reached 99.8% under mild conditions. Based on the results of GC–MS analysis, radical trapping experiments and electron spin resonance spectra, ^?O₂^? radicals were proved to be the main active species in the oxidation process, and a mechanism is proposed. Meanwhile, the recycling performance of 500‐TiO₂ was investigated, and no obvious decrease was observed after six recycles.     

Deep oxidative desulfurization of benzothiophene and dibenzothiophene with a peroxophosphotungstate–ionic liquid brush assembly

A novel, efficient and reusable heterogeneous catalytic assembly of peroxophosphotungstate held in an ionic liquid brush was synthesized and an extraction and catalytic oxidative desulfurization (ECODS) procedure was developed for a model oil of benzothiophene (BT) and dibenzothiophene (DBT) using 30 wt% hydrogen peroxide as terminal oxidant and methanol as solvent under mild conditions. Several factors that affect sulfur removal were investigated in detail. The highest sulfur removal can reach 100% for BT in 7 h at 70 °C when the molar ratio of H₂O₂, S and catalyst is 10:1:0.025. The sulfur removal for DBT can also reach 100% in 4 h at 50 °C with the same molar ratio of H₂O₂, S and catalyst. The experimental results demonstrate that this ECODS process has no apparent scale‐up effect. The catalyst can be easily recovered (via simple filtration) and recycled five times without a significant decrease in activity. Copyright © 2015 John Wiley & Sons, Ltd.     

反应控制相转移催化环氧化苯乙烯

研究了磷钨杂多酸盐反应控制相转移催化H2O2直接氧化苯乙烯制环氧苯乙烷的反应,考察了溶剂、H₂O₂用量、催化剂用量、反应温度、时间、苯乙烯浓度等因素对反应的影响。 获得的适宜的反应条件为：乙酸乙酯为溶剂,n(苯乙烯)∶n(H₂O₂)∶n(催化剂)=300∶300∶1,反应温度60 ℃,反应时间6 h,反应液中苯乙烯质量分数为10%。 在该条件下,苯乙烯的转化率为85.5%,环氧苯乙烷的选择性为84.9%。 催化剂可过滤回收,循环使用2次后的活性无明显下降。     

Regulating sulfur removal efficiency of fuels by Lewis acidity of ionic liquids

It is urgent to develop a new deep desulfurization process of fuels as the environmental pollution increases seriously. In this work, a series of Lewis acidic ionic liquids (ILs) [C₄³MPy]Cl/nZnCl₂ (n=1, 1.5, 2, 3) were synthesized and used in extraction and catalytic oxidative desulfurization (ECOD) of the fuels. The effects of the Lewis acidity of ILs, the molar ratio of H₂O₂/sulfur, temperatures, and different substrates including dibenzothiophene (DBT), benzothiophene (BT) and thiophene (TS), on sulfur removal were investigated. The results indicated that [C₄³MPy]Cl/₃ZnCl₂ presented near 100% DBT removal of model oil under conditions of 323 K, H₂O₂/DBT molar ratio 6:1. Kinetics for the removal of DBT, BT and TS by the [C₄³MPy]Cl/₃ZnCl₂-H₂O₂ system at 323 K is first-order with the apparent rate constants of 1.1348, 0.2226 and 0.0609 h^-1, and the calculated apparent activation energies for DBT, BT and TS were 61.13, 60.66, and 68.14 kJ/mol from 298 to 308 K, respectively. After six cycles of the regenerated [CC₄³MPy]Cl/₃ZnCl₂, the sulfur removal had a slight decrease. [CC₄³MPy]Cl/₃ZnCl₂ showed a good desulfurization performance under optimal conditions.     

Graphene wrapped phthalocyanine: Enhanced oxidative desulfurization for dibenzothiophene in fuel

Graphene wrapped metal phthalocyanine (MPc/RGO, M = Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) composites are synthesized by a facile ‘in situ hydrothermal’ method, using graphene oxide, M (CH₃COO)₂ and phthalic anhydride as the precursors. A biomimetic catalytic system of MPc/RGO and molecular O₂ have high activity for ultra‐deep removal of dibenzothiophene (DBT) in model oil containing n‐octane. Compared with pure graphene oxide and MPc, MPc/RGO composites displayed highly enhanced catalytic activity for the oxidation of dibenzothiophene in n‐octane. The conversion ratio of DBT was up to 97.51% after 180 min treatment at 60 °C and atmospheric pressure. The photostability of RGO/MPc composites photocatalystic degradation of dibenzothiophene was investigated. Mechanistic studies revealed that the RGO/MPc ? O₂ · species were the main active intermediate via the π‐π stacking interaction of MPc and RGO. The RGO wrapped phthalocyanine materials offer great potential as active photocatalysts for degradation of thiophene derivatives in fuel.