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.     

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.     

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.     

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.     

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.     

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     

双功能[Sn,Al]-Beta分子筛一步催化葡萄糖生成5-羟甲基糠醛

以部分脱铝的Beta分子筛为母体,采用同晶置换法将Sn植入骨架制备双功能[Sn,Al]-Beta分子筛,并应用于葡萄糖一步催化生成5-羟甲基糠醛(5-HMF)反应中.样品中Sn与Al的含量通过酸洗的浓度和酸洗的时间以及SnCl4处理的时间来控制.由于骨架中有与Al相关为B酸位,和Sn相关的L酸位,[Sn,Al]-Beta可作为一种双功能的固体酸催化剂.优化了[Sn,Al]-Beta催化葡萄糖一步催化生成5-HMF的反应参数,在最优Sn/Al比条件下,葡萄糖转化率为60.0%,5-HMF选择性为62.1%.     

Catalytic combustion of ethyl acetate over ceria-promoted platinum supported on Al2O3 and ZrO2 catalysts

Platinum-supported catalysts prepared by impregnation of mixed CeO₂/Al₂O₃ and CeO₂/ZrO₂ oxides using the sol-gel method were characterized and used in the combustion of ethyl acetate. In each series, the effect of CeO₂ loading (3 and 5 wt%) was studied. Characterization data from the studied catalysts (specific area measurements, hydrogen chemisorption, programmed temperature reduction (TPR), X-ray diffraction (XRD), photoelectron spectra (XPS) and transmission electron microscopy (TEM)) revealed significant changes in porosity and metal dispersion in each series. The catalytic activity of the solids, evaluated in the total combustion of ethyl acetate, exhibited a positive effect with the addition of Ce in the zirconia series whereas no significant changes was observed in the alumina series.     

Influence of ceria modification on the properties of TiO2-ZrO2 supported V2O5 catalysts for selective catalytic reduction of NO by NH3

TiO(2)-ZrO(2) (hereafter denoted as Ti-Zr) supported V(2)O(5) catalysts with different loadings of CeO(2) were synthesized, and their physicochemical properties were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), in situ Fourier transform infrared spectroscopy (in situ FT-IR) and temperature-programmed reduction (TPR). Their catalytic activities toward the NO(x) reduction reaction with NH(3) were tested. We found that with the addition of CeO(2), more NO was removed in a wide temperature range of 220-500 °C. As the CeO(2) content was increased from 10% to 20% (i.e., the molar ratio of Ce to Ti-Zr), NO conversion increased significantly; after that, increasing CeO(2) content, however, decreased NO conversion. In particular, the addition of CeO(2) to V(2)O(5)/Ti-Zr suppressed the coke deposition and rendered a stable and high catalytic activity. The characterization results indicated that: (1) the deposited vanadium and cerium oxides were highly dispersed over the Ti-Zr support, and in addition to ZrV(2)O(7), a common binary compound observed in V(2)O(5)/Ti-Zr, CeVO(4) and Ce(3)ZrO(8) was formed upon increasing CeO(2) content; (2) the introduction of CeO(2) to V(2)O(5)/Ti-Zr sample promoted the redox ability of the resulting catalysts; and (3) the Ce-containing catalysts possessed the greater amount of surface acidic and active intermediate.     

Thermal behaviour of high surface area V2O5/TiO2 catalysts

Thermal analysis (TG and DTA) was employed for the characterization of V₂O₅/TiO₂ catalysts supported on high surface area TiO₂. The results obtained are consistent with a uniform spreading of vanadium oxide on TiO₂ surface for V₂O₅ content less than 15% by weight.The presence of V₂O₅ on the surface of TiO₂ affects the anatase-rutile phase transition lowering the temperature at which it occurs.DTA measurements, performed on catalysts after many months from the preparation, show the appearance of an exothermic peak in the range 280°–340°C. This signal has been related to the oxidation of V(IV) to V(V) on the catalyst surface.Catalysts characterization, performed by chemical analysis and FT-IR spectroscopy, has confirmed this interpretation.It has been suggested that a slow modification of the catalyst occurs, leading to an increase of the V(IV) content during the time.

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Zusammenfassung Zur Charakterisierung von V₂O₅/TiO₂-Katalysatoren auf hochoberflächigem TiO₂ Trägermaterial wurde die Thermoanalyse (TG und DTA) angewendet. Für einen V₂O₅-Gehalt von weniger als 15 Gew.% entsprechen die erhaltenen Ergebnisse einer gleichmäßigen Verteilung des Vanadiumoxides an der TiO₂-Oberfläche.Die Gegenwart von V₂O₅ an der Oberfläche von TiO₂ beeinflußt die Anatas-Rutil-Phasenumwandlung, indem sie die zugehörige Temperatur verringert.DTA-Messungen an Katalysatoren mehrere Monate nach ihrer Herstellung zeigten das Auftreten eines exothermen Peaks im Bereich 280°–340°C. Dieses Signal wurde der Oxidation von V(IV) zu V(V) an der Katalysatoroberfläche zugeschrieben.Diese Interpretation konnte durch eine Charakterisierung des Katalysatoren durch chemische Analyse und FT-IR-Spektroskopie bestätigt werden.Es wurde angedeutet, daß der Katalysator mit der Zeit einer langsamen Modifikation unterliegt, die zu einem Ansteigen des V(IV)-Gehaltes führt.

     

Study of properties of Al2O3 and TiO2 supported palladium catalysts in reactions of tetrachloromethane hydrogenation

Properties of Al₂O₃- and TuO₂-supported palladium catalysts modified with calcium oxide were studied. Catalyst samples 2% Pd/CaO-TiO₂ and 2% Pd/CaO-Al₂O₃ were examined by the methods of temperature-programmed reduction in a flow of hydrogen, temperature-programmed desorption of ammonia and carbon(IV) oxide, and X-ray diffraction analysis.     

Emergence of CO2 electrolyzers including supported molecular catalysts

With access to cheap, sustainable electricity, electrocatalysis is a promising technology for converting electric power into storable chemical fuels or value-added chemical compounds. This has sparked the development of electrocatalysts that need to operate at high product selectivity and high energy efficiency. Electrocatalytic alcohol oxidation, oxygen activation and nitrogen and carbon dioxide (CO₂) reduction are examples of reactions with a huge industrial potential. Notably, electrocatalytic reduction of CO₂ has recently developed as a favourable pathway to convert this greenhouse gas into value-added chemicals and fuels. Earth-abundant metals stabilized by carbon/nitrogen macrocycle ligands are well-known efficient and selective catalysts for the electrochemical reduction of CO₂ in homogeneous conditions. Recently, such catalysts have also been used in supported conditions and implemented in flow cell electrolyzers, showing promising performances. This review provides a synopsis for the evolution of CO₂ electrolyzers using molecular catalysts.