氧化铝负载催化剂作用下以甲醇为烷基化试剂的苯酚气相转化制备苯甲醚(英文)

苯甲醚作为重要的化学品和医药中间体而广泛应用于香料、调味剂及有机合成.液相法是传统的苯甲醚制备工艺,例如在碱性环境下,通过酚钠与硫酸二甲酯反应,溴苯与甲醇反应,酚钠与氯代甲烷反应均可制得苯甲醚.然而,这些方法具有环境处理负担较重和所用原料毒性较强等不足而备受限制.因此,环境友好的绿色苯甲醚合成工艺的开发成为必然,苯酚的气相烷基化工艺由此提出.其中,以碳酸二甲酯(DMC)为烷基化试剂的苯酚气相转化苯甲醚制备方法最受关注.DMC是常用的绿色高效烷基化试剂,但其价格相对较高,在一定程度上增加了苯甲醚制备工艺的复杂性和产品成本.鉴于DMC可由甲醇经氧化羰基化制得,因此以甲醇为烷基化试剂的苯酚气相烷基化转化制备苯甲醚方法成为另一研究热点.然而,与DMC的烷基化性能相比,以甲醇为烷基化试剂的反应产物分布较为复杂,作为苯酚O-烷基化(在苯酚的羟基氧原子上发生的烷基化)产物的苯甲醚相对较难获得,而苯酚的C-烷基化(在苯酚的芳环上发生的烷基化)产物甲基酚产率更易提高.总体而言,与DMC烷基化方法相比,以甲醇为烷基化试剂的苯酚气相转化制备苯甲醚方法有待改善,相关反应机理也更欠明晰,因此具有重要的研究价值.本文研究了γ-Al_2O_3(AA)负载型催化剂上以甲醇为烷基化试剂的苯酚气相转化制备苯甲醚方法,考察了反应温度、气体空速、苯酚与甲醇配比以及催化剂中K负载量和焙烧温度等对反应性能的影响,并分析了该体系中的反应机理.研究表明,在AA上负载的8种化合物(NaCl,MgCl_2,Fe_2(SO_4)_3,Co(NO_3)_2,ZnCl_2,La(NO_3)_3,Ce(NO_3)_3和KH_2PO_4)的催化剂中,KH_2PO_4/AA的催化性能最佳,相应催化剂中K离子负载量为7.53 wt%,于700 oC焙烧8 h.苯酚与甲醇气相反应过程中,苯甲醚最大收率出现在400–450 oC,且随甲醇与苯酚的摩尔比升高而增加,但随空速的提高而降低.另外,在KH_2PO_4/AA催化剂的高K含量,以及低温、高空速、低甲醇含量的物料配比的条件下,对苯酚的O-烷基化过程有利.产物除主产物苯甲醚以外,还有少量甲基苯酚、甲基苯甲醚以及二甲基苯酚等副产物.在K含量为7.53 wt%的KH_2PO_4/AA催化剂作用下,苯甲醚收率最高时反应条件为400–450 oC,空速小于0.18 h儃1,甲醇与苯酚摩尔配比为5.本文所开发的催化剂制备方法简单,反应条件温和,产物收率较高,因此具有较好的应用前景.X射线衍射结果显示,经高温焙烧及固相反应后,KH_2PO_4/AA催化剂中产生了K_3Al_2(PO_4)_3新物相.推测该反应机理是酸性氧化铝促进甲醇脱羟基负离子以及K离子促进酚羟基脱氢质子,所形成的甲基正离子进一步与苯氧基负离子结合得到苯甲醚的"钾离子-酸"双功能催化作用过程     

Polymer supported catalysts for oxidation of phenol and cyclohexene using hydrogen peroxide as oxidant

Polymer supported transition metal complexes of N,N′-bis (o-hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by anchoring its amino derivative Schiff base (AHPHZ) on cross-linked (6 wt%) polymer beads and then loading iron(III), copper(II) and zinc(II) ions in methanol. The loading of HPHZ Schiff base on polymer beads was 3.436 mmol g⁻¹ and efficiency of complexation of polymer anchored HPHZ Schiff base for iron(III), copper(II) and zinc(II) ions was 83.21, 83.40 and 83.17%, respectively. The efficiency of complexation of unsupported HPHZ Schiff base for these metal ions was lower than polymer supported HPHZ Schiff base. The structural information obtained by spectral, magnetic and elemental analysis has suggested octahedral and square planar geometry for iron(III) and copper(II) ions complexes, respectively, with paramagnetic behavior, but zinc(II) ions complexes were tetrahedral in shape with diamagnetic behavior. The complexation with metal ions has increased thermal stability of polymer anchored HPHZ Schiff base. The catalytic activity of unsupported and polymer supported HPHZ Schiff base complexes of metal ions was evaluated by studying the oxidation of phenol (Ph) and epoxidation of cyclohexene (CH). The polymer supported metal complexes showed better catalytic activity than unsupported metal complexes. The catalytic activity of metal complexes was optimum at a molar ratio of 1:1:1 of substrate to oxidant and catalyst. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) in oxidation of phenol and epoxidation of cyclohexene was better with polymer supported metal complexes in comparison to unsupported metal complexes. The energy of activation for oxidation of phenol (22.8 kJ mol⁻¹) and epoxidation of cyclohexene (8.9 kJ mol⁻¹) was lowest with polymer supported complexes of iron(III) ions than polymer supported Schiff base complexes of copper(II) and zinc(II) ions.     

Regioselective Friedel-Crafts alkylation of indoles with epoxides using nano MgO

Abstract

3-Alkylindole derivatives were produced by ring opening of epoxides in the presence of magnesium oxide nanoparticles as an efficient catalyst. Solvent-free conditions, stoichiometric amounts of reactants, and improved reaction times and yields are the most important advantages of this method. MgO nanoparticles are synthesized successfully. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer- Emmet-Teller (BET) surface measurement were used to characterize the structure and morphology of the catalyst.     

Phase Diagram at Low Temperature of the System ZrO2/Nb2O5

Various compositions of the ZrO₂/Nb₂O₅ system were synthesized and the experimental conditions for obtaining reproducible results were established. The gel was precipitated at constant pH = 10, aged at room temperature for 18 h and, after filtration, dried at 110 °C for 24 h. The phase diagram of the ZrO₂/Nb₂O₅ system was established between 600 and 1300 °C. Phase transitions of ZrO₂ and Nb₂O₅ were observed with XRD; and two ternary compounds, 6 ZrO₂ · Nb₂O₅ and 12 Nb₂O₅ · ZrO₂, were identified. The samples with a Nb₂O₅ content between approximately 10 and 40 mole% showed the greatest specific area and are thus best for use as catalyst supports.     

沉积-沉淀法和沉积-还原法制备Nb2O5负载的金纳米粒子及其催化CO氧化活性

采用不同的沉积法制备了氧化铌(Nb2O5)负载的金纳米粒子催化剂,即沉积-沉淀(DP)法、尿素辅助的DP法、沉积-还原(DR)法和一步法制备了1 wt%Au/Nb2O5催化剂.在众多类型Nb2O5(包括商业Nb2O5)中,采用水热法制备的层间型Nb2O5(Nb2O5(HT))最适合用作载体.结果表明,较大比表面积的Nb2O5(HT)使得金以纳米颗粒形式分散于其上.在优化的条件下,以DP和DR法沉积于Nb2O5(HT)上的金纳米粒子平均粒径为5 nm.采用DR法制备的Au/Nb2O5(HT)催化剂上CO转化率为50%时的温度为73oC.不沉积金的条件下,即使在250oC, Nb2O5(HT)对CO氧化反应也没有催化活性.因此,金的沉积对活性的促进作用非常明显.该简易Au/Nb2O5催化剂将金催化剂的类型扩展到酸性载体,这将增加新的应用.     

不同沉淀剂制备的 Co3O4低温催化氧化甲醛

室内空气中低浓度甲醛严重危害人类健康,高效去除甲醛成为人们关注的课题.在各种去除甲醛的方法中,吸附法简单快速,但是存在饱和吸附量的限制;光催化降解法能够去除低浓度甲醛,却会产生一些如臭氧等二次污染物;低温催化氧化甲醛由于其高效和产物矿化完全而成为具有实际应用前景的技术.虽然贵金属负载型催化剂具有室温去除甲醛的能力,可是高昂的成本使其难以大规模应用.过渡金属氧化物因其良好的催化氧化性能和较低的成本逐渐成为研究重点.
　　近期研究发现,含钴的氧化物具有较高的催化氧化甲醛能力,同时一些碱金属如钠或钾的加入可增加催化剂表面羟基物种,从而有效促进了甲醛氧化.沉淀法具有操作简单和条件易于控制等特点,因此本文选取不同的沉淀剂(NH3·H2O, KOH, NH4HCO3, K2CO3, KHCO3)采用沉淀法制备了 Co3O4催化剂并进行了甲醛催化氧化性能测试.采用 X射线衍射(XRD)、原子吸收光谱(AAS)、氢气程序升温脱附(H2-TPD)、X射线光电子能谱(XPS)和原位漫反射红外光谱(in suit-DRIFTS)等表征手段探讨了不同沉淀剂制备的催化剂催化甲醛氧化性能差异的原因.
　　结果显示,在以 KHCO3为沉淀剂制备的 Co3O4催化剂(KHCO3-Co)上甲醛(100 ppm)完全氧化成 CO2的温度为90°C,明显优于其他样品.在以 NH4HCO3为沉淀剂制备的 Co3O4表面负载2 wt%的 K2CO3后(PC/AHC-Co)具有和 KHCO3-Co相似的催化性能. XRD结果表明,各沉淀剂制备的 Co3O4均为尖晶石型,晶粒尺寸约为18nm,衍射峰位置无明显偏移说明没有其他金属离子掺杂进 Co3O4晶体.结构表征还表明,采用含碳酸根或碳酸氢根离子试剂制备的样品具有较高的比表面积、孔体积和孔径,可能是焙烧阶段碳酸钴分解产生大量 CO2形成的,而负载 K2CO3的样品各参数均大幅降低,说明表面 K2CO3填补或堵塞了部分孔结构. AAS结果表明, KHCO3-Co和 PC/AHC-Co所含 K离子浓度相近并显著高出其他沉淀剂制备样品, XPS结果也证明了这一点.这可能是由于在用 KHCO3沉淀钴离子的过程中,钾离子裹挟在沉淀物中不易被洗涤干净,并且保留在焙烧后的样品中. H2-TPR和 XPS结果显示,用 KHCO3作为沉淀剂时可以增加 Co3O4催化剂表面 Co3+/Co2+比例从而提高了氧化能力,虽然本文 PC/AHC-Co样品有着最高的 Co3+/Co2+比例,但相对较低的比表面积和孔径减少了活性中心,使得其活性与 KHCO3-Co相似.insuit-DRIFTS结果表明, NH4HCO3-Co催化剂上羟基基团在甲醛吸附阶段会被大量消耗,并有二氧亚甲基(DOM)中间物种大量生成.在氧化阶段,随着温度升高, DOM逐渐减少,而甲酸盐和碳酸氢盐物种逐渐增多,最后各物种趋近催化剂的初始状态.在 KHCO3-Co催化剂上,甲醛吸附阶段有大量 DOM和甲酸盐物种生成,而羟基基团消耗并不明显.在氧化阶段随着温度升高, DOM逐渐减少,甲酸盐逐渐增多并最后消失,整个过程并未观测到碳酸氢盐物种生成.这说明 KHCO3-Co样品在催化氧化甲醛反应中能够再生羟基基团,进而提高了催化氧化甲醛活性.
　　综上所述,以 KHCO3为沉淀剂制备的 Co3O4样品具有最佳的甲醛催化氧化性能,其在沉淀过程中样品上会残留一定量钾离子,其作用与在 Co3O4表面负载相当量的 K2CO3相似. Co3O4催化氧化甲醛活性高的主要原因是催化剂表面存在 K+和 CO32-并且具有适当的 Co3+/Co2+混合价态.     

Phosphorus pentoxide supported on silica gel and alumina (P2O5/SiO2, P2O5/Al2O3) as useful catalysts in organic synthesis

Phosphorus pentoxide supported on silica gel or alumina (P₂O₅/SiO₂, P₂O₅/Al₂O₃) has been used in many organic transformations as versatile solid catalysts. These catalysts have received considerable attention as an inexpensive, eco-friendly, highly reactive, easy to handle and non-toxic acid catalyst for various organic transformations, affording the corresponding products in excellent yields and high selectivity. In this review, some applications of these catalysts in organic reactions are discussed.     

CoAl2O4/Al2O3载体对钴基费托催化剂反应性能影响的研究

通过浸渍和高温焙烧,制得表面附着CoAl₂O₄微晶颗粒的改性Al₂O₃载体,并采用等体积浸渍法制备负载型Co基催化剂。结合 N₂物理吸附、XRD、H₂-TPR、XPS及H₂化学吸附等表征手段,研究改性载体及其负载钴基催化剂的织构特征;采用费托合成反应评价其催化性能。结果表明,Al₂O₃改性后,表面CoAl₂O₄的存在有效减少了载体与活性组分Co的相互作用,显著提高了催化剂的还原度和催化活性。载体的改性量在20%左右达到最佳值,继续增加,催化剂还原度和活性基本不再升高。载体改性促使催化剂CH₄选择性有所降低,C₅₊选择性略有提高。     

Ni-Nb2O5和Ni-Cu-Nb2O5催化甲烷燃烧活性研究

在微型固定床反应器中考察了新型甲烷催化燃烧催化剂Ni-Nb2O5和Ni-Cu-Nb2O5的活性．实验结果表明，含Nb2O5的Ni及Ni-Cu双金属催化剂具有好的催化甲烷低温燃烧性能，其甲烷转化率与反应温度、活性组分含量和空速有关．70％Ni担载量的Ni-Nb2O5催化剂可使甲烷在500℃时完全转化，并具有稳定的催化活性．Ni-Cu-Nb2O5体系催化剂中，Ni／Cu比为65／25时催化剂具有最佳的活性；该催化剂中Nb2O5可以在一个比较宽的范围内调节，并在此调节范围内可使甲烷在550℃温度下完全转化．     

Catalytic enantioselective Friedel-Crafts alkylation at the 2-position of indole with simple enones

A procedure for the enantioselective alkylation of indole at the 2-position with simple non-chelating enones is described for the first time. Reaction between 4,7-dihydroindole and enones in the presence of zirconium(IV)-BINOL complexes, followed by a p-benzoquinone oxidation gives indoles alkylated at the 2-position with good yields and moderate enantioselectivities.     

Para-selectivity of SAPO-5 and mordenite catalysts in the alkylation of cumene with 2-propanol

Alkylation of cumene with 2-propanol was studied on SAPO-5 and mordenite catalysts. The primary products of the alkylation on every catalyst examined here were p- and m-diisopropylbenzene (DIPB) in a ratio of 75:25. The p-DIPB fraction in DIPB isomers (para-selectivity) decreased with increasing yield of DIPB, due to the secondary reaction of p-DIPB to m-DIPB. On SAPO-5, mordenite and silica-alumina, this secondary reaction proceeds through dealkylation of p-DIPB to cumene, followed by re-alkylation of the resultant cumene to m-DIPB. The dealkylation of p-DIPB would occur preferentially over that of m-DIPB. This was due to the higher reactivity of p-DIPB and probably to the reactant molecular shape selectivity of SAPO-5 and mordenite. The para-selectivity was improved by supporting boron oxide on SAPO-5 and mordenite; this improvement was caused by suppression of the secondary dealkylation of p-DIPB.     

Mesoporous Pt-SiO2 and Pt-SiO2-Ta2O5 catalysts prepared using Pt colloids as templates.

Sol‐gel synthesis of silica and silica–tantalum oxide embedded platinum nanoparticles is carried out using Pt colloids as templates. These colloids are prepared by reduction with Na[AlEt₃H] and stabilized with different ligands (ammonium halide derivatives, non‐ionic surfactants with polyether chains, and 2‐hydroxy‐propionic acid). The aim of the present study is to prepare mesoporous silica embedded Pt colloids combining the “precursor concept” with the model of catalyst preparation using preformed spheres. Nanoparticles of Pt incorporated in high surface area mesoporous materials are formed after calcination. Further, it is observed that calcination of these catalysts causes partial aggregation and oxidation of the parent colloids, a process that is largely dependent on the nature of the stabilizing ligands. Several methods have been used for characterization of these materials: adsorption‐desorption isotherms at 77 K, H₂ chemisorption, X‐ray diffraction(XRD), ²⁹Si and ¹³C magic angle spinning (MAS) NMR, ammonia diffuse reflectance Fourier transform infrared spectroscopy (NH₃‐DRIFT), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS). It is found that both metal oxide systems exhibit Brønsted acidity (weaker for silica and quite strong for silica–tantalum oxide). In addition, NH₃‐DRIFT experiments demonstrate the oxidative properties of the surface. Part of the adsorbed NH₄⁺ species is oxidized to N₂O. Testing these catalysts in the reduction of NO and NO₂ with isopentane under lean conditions indicate that the activity of these catalysts is indeed dependent on the size of the platinum particles, with those of size 8–10 nm demonstrating the best results. The support likely contributes to this effect, particularly after Ta incorporation into silica.     

Aerobic cascade oxidation of substituted cyclopentane-1,2-diones using metalloporphyrin catalysts

A method for the aerobic cascade oxidation of cyclopentane-1,2-diones using metal porphyrins as catalysts, yielding hydroxydiacids 2, ketoacid 3 and diketoacids 4 which are the intermediates of important biologically active compounds is reported. This method is operationally simple and can be employed under ambient conditions.     

Autothermal reforming of methane over Ni catalysts supported over ZrO2-CeO2-Al2O3

Ni catalysts supported on Al2O3, ZrO2-Al2O3, CeO2-Al2O3 and ZrO2-CeO2-Al2O3 were prepared by coprecipitation method, and their catalytic performances for autothermal reforming of methane to hydrogen were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. The relationship between the structures and catalytic activities of the catalysts was discussed. The results showed that the catalytic activity and stability of the Ni/ZrO2-CeO2-Al2O3 catalyst was better than those of other catalysts with the highest CH4 conversion, H2/CO and H2/COx ratio at 750 ℃. The catalyst showed a little deactivation along the reaction time during its 72 h on stream with the mean deactivation rate of 0.08%/h. The catalytic performance of the Ni/ZrO2-CeO2-Al2O3 catalyst was also affected by reaction temperature, no2 ： nCH4 molar ratio and nH2O ： nCH4 molar ratio. TPR, XRD and XPS measurements indicated that the formation of ZrO2-CeO2 solid solution could improve the dispersion of NiO, and inhibit the formation of NiAl2O3, and thus significantly promoted the catalytic activity of the Ni/ZrO2-CeO2-Al2O3 catalyst.     

Rare earth metal triflates catalyzed electrophilic nitration using N2O5

A mild,efficient and eco-friendly process for the electrophilic nitration is described using N₂O₅ as a green nitrating agent in the presence of rare earth metal triflates[RE（OTf）₃]under mild conditions.     

Determination of surface V=O species of V2O5 catalysts during reaction condition by using in-situ Narp technique

NARP (Nitric oxide-Ammonia Rectangular Pulse) technique was applied for the in-situ measurement of the number of surface V=O species of V₂O₅ catalysts. When V₂O₅ catalyst was exposed to flowing benzene/O₂/N₂ mixture gas at 573–673 K, the surface concentration of V=O species decreased and finally reached a steady state which was dependent on the [O₂]/[Benzene] ratio in the feed gas. It was confirmed by XPS spectra that the decrease in the surface V=O species is attributed to the reduction of the V₂O₅ surface. Although calcination of V₂O₅ at above 873 K reduced the surface concentration of V=O species, it recovered after a cyclic reduction-oxidation treatment at 673 K, which modifies the near-surface layer of V₂O₅. The dependence of the surface V=O species on calcination temperature was correlated with the flatness of the surface and the diffusion of lattice oxygen in near-surface layer.     

In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states

Niobium oxide (Nb₂O₅) films and powders have been obtained via the sol-gel route from an NbCl₅ precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500  °C and 800  °C, respectively, while at 300  °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb₂O₅ in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb₃-O stretching modes and the appearance of polaron absorption were noted with Li⁺ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail. Received: 21 August 1997 / Accepted: 9 October 1997     

Synthesis of five-membered N-heterocycles using Rh based metal catalysts

Abstract

One of the highly emerging and an important aspect of organic chemistry is the metal catalyzed synthesis of heterocycles. The methodologies used earlier for their synthesis were less approachable to the organic chemist because of their high cost, highly specified instrumentation, and inconvenient methods. For both the stereoselective and regioselective synthesis of five-membered nitrogen containing heterocycles, cyclic reactions that are Rh-catalyzed have known to be very efficient. The present review covers the varied applications of Rh as a catalyst and its importance in the formation of five-membered nitrogen containing heterocycles. The fascinating research that has been done in this area is enclosed in this review.