MCM-41分子筛负载亚硒核过氧钨酸盐催化剂催化二苯并噻吩氧化脱硫

石油在作为燃料使用过程中常常产生各种污染,特别是油品中的含硫化合物不仅会降低油品品质,而且燃烧后产生的硫氧化物可污染大气,形成酸雨,危害人类健康.因此,油品深度脱硫是一项十分重要而紧迫的工作.
　　目前油品脱硫方法有很多种,主要分为加氢脱硫与非加氢脱硫.加氢脱硫反应条件苛刻,脱硫效率低,对设备要求高,因而非加氢脱硫正在被广泛研究.其中氧化脱硫反应条件温和,脱硫效率高,对设备要求不高,有望实现规模化应用.在氧化脱硫反应中,催化剂是研究重点,尤其是催化剂效率及可回收能力.本课题组合成的亚硒核过氧钨酸盐是一种具有高选择性和高催化活性的催化剂,但它在反应后无法实现回收再利用,从而限制了其广泛应用.为了提高该催化剂的可回收能力,本文尝试制备负载型亚硒核过氧钨酸盐用于氧化脱硫反应中,考察其催化效率及可回收能力.
　　分子筛具有孔结构,比表面积大且较为稳定,是理想的催化剂载体.本文采用浸渍法制备了MCM-41分子筛负载的亚硒核过氧钨酸盐,为了提高负载能力,减少催化剂溶脱,还制备了MCM-41-NH2分子筛负载的亚硒核过氧钨酸盐,并运用红外光谱、X射线衍射、N2吸附-脱附和透射电镜对它们进行了表征.结果显示,亚硒核过氧钨酸盐在MCM-41和MCM-41-NH2分子筛内分散均匀,表明负载成功.将负载型亚硒核过氧钨酸盐催化剂用于模拟油样二苯并噻吩(DBT)氧化脱硫实验,并用气相-火焰光度检测仪跟踪实验.结果表明,负载型和非负载型催化剂均具有较高的催化性能.模拟油样在负载型催化剂作用下氧化脱硫反应2 h后, DBT转化率达98.7%,实现了深度脱硫.此外,还优化了反应时间、反应温度及氧化剂和催化剂用量.与其它催化剂相比,在相似脱硫效率情况下,负载型催化剂的催化效率更高,反应条件更加温和,催化剂用量更少,因而更加环保和节能.对反应产物进行了红外光谱、气相-质谱联用分析以及气相色谱保留时间对比分析,结果表明DBT脱硫反应产物为DBTO2.结合相关文献,对该催化剂上DBT氧化脱硫提出了一种可能的催化氧化反应机理.
　　反应后将负载型催化剂回收过滤,洗涤和干燥后,进行下一轮氧化脱硫反应.结果表明, MCM-41分子筛负载的亚硒核过氧钨酸盐在循环使用过程中, DBT转化率下降较快,循环使用4次后, DBT转化率降至80%,而MCM-41-NH2分子筛负载的催化剂在循环使用4次后, DBT转化率仍达90%.这表明MCM-41-NH2分子筛负载的亚硒核过氧钨酸盐催化剂具有更好的稳定性和回收使用性能.
　　综上所述,负载型亚硒核过氧钨酸盐是一种高效的氧化脱硫催化剂,在较为温和的反应条件下即可实现深度催化氧化脱硫,其循环使用性能也得到明显提高.本结果可为该催化剂未来在工业上广泛应用提供一定参考.     

Copper catalyzed oxidation of sulfides to sulfoxides with aqueous hydrogen peroxide

Copper(II) complex 1 catalyzes the oxidation of sulfides to sulfoxides with 30% H₂O₂ in high yields. Addition of a catalytic amount of TEMPO to the reaction mixture enhances the conversion and selectivity. Complex 1 can be recycled without loss of activity.     

Peroxotungstate immobilized on ionic liquid-modified silica as a heterogeneous epoxidation catalyst with hydrogen peroxide

Peroxotungstate immobilized on ionic liquid-modified SiO2 is capable of heterogeneously epoxidizing a wide range of olefins with the maintenance of the catalytic activity of homogeneous analogue. The epoxidation was immediately stopped by the removal of the catalyst, and no tungsten species could be found in the filtrate after the removal of the catalyst. These results can rule out any contribution to the observed catalysis from the tungsten species that leached into the reaction solution, and the observed catalysis is truly heterogeneous in nature. Furthermore, the catalyst was reusable without the loss of the catalytic performance.     

Selective and mild oxidation of thiols to sulfonic acids by hydrogen peroxide catalyzed by methyltrioxorhenium

Aromatic and aliphatic thiols are oxidized in acetonitrile at 20 °C by hydrogen peroxide in the presence of methyltrioxorhenium as the catalyst to yield the corresponding sulfonic acids in high isolated yields (85-94%).     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-aniline complex

Sn-aniline complex was prepared by a simple procedure.Cyclic and acyclic ketones were oxidized into lactones or esters with very high selectivity and yield with 30% hydrogen peroxide in the presence of Sn-aniline complex.     

Highly efficient C-H insertion reactions of hydrogen peroxide catalyzed by homogeneous and heterogeneous methyltrioxorhenium systems in ionic liquids

A convenient and efficient C-H insertion reaction of environment friendly H₂O₂ into representative hydrocarbon derivatives by homogeneous methyltrioxorhenium (MTO), heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium (PVP/MTO) and microencapsulated polystyrene/methyltrioxorhenium (PS/MTO) systems in ionic liquids, is described. In some cases a higher activity was observed if compared with the same reaction in molecular solvents. The heterogeneous catalysts are stable systems under the reaction conditions and can be recycled for more transformations.     

Indirect catalytic epoxidation with hydrogen peroxide electrogenerated in ionic liquids

Hydrogen peroxide was generated in room temperature ionic liquids by electrolysis, which was then used for the epoxidation of lipophilic alkenes under a carbon dioxide-saturated environment and in the presence of catalytic amount of manganese salt. ¹³C NMR showed that the active peroxymonocarbonate (HCO₄⁻) was generated from the mixture of H₂O₂, CO₂, and water in the ionic liquids. Most lipophilic alkenes were selectively epoxidized within 4-5 h. The ionic liquids can be recovered and reused without any deterioration in the performance.     

Selective oxidation of sulfides to sulfoxides and sulfones using 30% aqueous hydrogen peroxide and silica-vanadia catalyst

A green, efficient and selective approach for the oxidation of sulfides to sulfoxides and sulfones with stoichiometric amount of 30% aq. H₂O₂ is reported. The reaction is performed in methanol with silica-vanadia as heterogeneous and reusable catalyst.     

Oxidation of caffeine with hydrogen peroxide catalyzed by metalloporphyrins

The biomimetic oxidation of caffeine with hydrogen peroxide using metalloporphyrins as catalysts, which are known to be good biomimetic models of cytochrome P450 enzymes, is investigated. The two manganese porphyrins tested, chloro[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(III), [Mn(TDCPP)Cl], and chloro [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]manganese(III), [Mn(TPFPP)Cl], afford high conversions of caffeine for all substrate/catalyst molar ratios. Selectivity was found to be dependent on the catalyst employed, and a new spiro racemic compound is described and fully characterized in the solid state from X-ray diffraction studies.     

Enantioselective oxidation of sulfides with hydrogen peroxide catalyzed by vanadium complex of sterically hindered chiral Schiff bases

Sterically hindered chiral Schiff base ligands 4a-d were prepared from an aldehyde derived from BINOL. The vanadium complexes of the ligands catalyze an efficient, enantioselective H₂O₂-promoted sulfoxidation of alkyl aryl sulfides, and enantioselectivities as high as 98-99% ee are observed in the sulfoxidation of benzyl aryl sulfides.     

Biomimetic oxidation of metribuzin with hydrogen peroxide catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides

The biomimetic oxidation of metribuzin, a pre- and post-emergence herbicide with hydrogen peroxide catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides [TAPFe(III)Cl], has been studied yielding 6-t-butyl-3-methylthio-1,2,4-triazine-5(4H)-one, 4-amino-6-t-butyl-3,5(2H,4H)-dione and 6-t-butyl-1,2,4-triazin-3,5(2H,4H)-dione under various reaction conditions.     

Selective synthesis of sulfoxides and sulfones by tantalum(V) catalyzed oxidation of sulfides with 30% hydrogen peroxide

The reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum(V) chloride in acetonitrile, i-propanol, or t-butanol selectively provided the corresponding sulfoxides in high yields. On the other hand, the reaction of sulfides with 30% hydrogen peroxide-catalyzed by tantalum(V) chloride or tantalum(V) ethoxide in methanol effectively gave the sulfones.     

Alcohols oxidation with hydrogen peroxide promoted by TPAP-doped ormosils

Organically modified silica gels doped with TPAP (tetra-n-propylammonium perruthenate) are effective catalysts for the oxidation of alcohols by hydrogen peroxide at room temperature, provided that the oxidant H₂O₂ solution is added slowly. The effect of the surface catalyst polarity is the opposite of that found in aerobic alcohols oxidation and is consistent with the polar nature of the primary oxidant.     

Highly selective and efficient oxidation of sulfides with hydrogen peroxide catalyzed by a chromium substituted Keggin type polyoxometalate

The catalytic oxidation of sulfides into the corresponding sulfones by a chromium substituted Keggin type polyoxometalate, (TBA)₄[PW₁₁CrO₃₉]·3H₂O, was achieved using mild reaction conditions. Excellent yields were obtained using four equivalents of 30% H₂O₂. Under these reaction conditions, the sulfide group was highly reactive and other functional groups such as hydroxyl or a double bond were unaffected. Using a commercially available, eco-friendly, and cheap oxidant, mild reaction conditions, operational simplicity, practicality, short reaction times, high to excellent yields, and excellent chemoselectivity are some of the advantages of this catalytic system.     

Selective oxidation of naphthalene derivatives with ruthenium catalysts using hydrogen peroxide as terminal oxidant

The selective oxidation of naphthalene and its derivatives to give naphthoquinones has been investigated in detail. The reaction can be carried out effectively in the presence of a catalytic amount of Ru complexes (0.2 mol%) and phase transfer catalysts (PTC) using H₂O₂ as the terminal oxidant and water as the solvent. The effect of different ruthenium complexes, phase transfer catalysts, and the concentration of hydrogen peroxide were studied. Compared to previous procedures for this type of reactions, acidic solvents and high concentration of hydrogen peroxide are not necessary, which makes the reaction more environmentally friendly.     

First enantioselective iron-porphyrin-catalyzed sulfide oxidation with aqueous hydrogen peroxide

The asymmetric oxidation of sulfides by H(2)O(2) to give optically active sulfoxides (ee up to 90%) was carried out in methanol and water using chiral water-soluble iron porphyrins as catalysts.     

Tantalum(V) or niobium(V) catalyzed oxidation of sulfides with 30% hydrogen peroxide

Tantalum(V) and niobium(V) are effective catalysts for the oxidation of sulfides with 30% hydrogen peroxide. The reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum(V) chloride or niobium(V) chloride in acetonitrile, i-propanol or t-butanol selectively provided the corresponding sulfoxides in high yields. The corresponding sulfones are efficiently obtained from the reaction of sulfides with 30% hydrogen peroxide in methanol catalyzed by tantalum(V) or niobium(V).     

Quinones synthesis via hydrogen peroxide oxidation of dihydroxy arenes catalyzed by homogeneous and macroporous-polymer-supported ruthenium catalysts

Ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dm-Pheox) complex 2a and its macroporous-polymeric-catalyst 4 were found to be very rapid and efficient catalysts in the hydrogen peroxide oxidation of 1,2- and 1,4-dihydroxy arenes. Most of the quinone products were delivered in 99% yield. The polymeric-catalyst 4 could be reused at least five times.