Catalytic properties of platinum-promoted acid cesium salts of molybdophosphoric and molybdovanadophosphoric heteropoly acids in the gas-phase oxidation of benzene to phenol with an O<Subscript>2</Subscript> + H<Subscript>2</Subscript> mixture

Acid salts Cs _x H_{3 + n ? x} PMo_{12 ? n} V _n O₄₀ (n = 0, 1, 2, or 3; x = 2.5 or 3.5) with coprecipitated or supported platinum were studied using thermogravimetry, IR spectroscopy, and temperature-programmed reduction. The thermal region of the full stability of these salts is limited by the decomposition temperature of the corresponding acid H₃PMo₁₂O₄₀ (～400°C) or H_{3 + n} PMo_{12 ? n} V _n O₄₀ (～300–350°C). The degree of reduction of heteropoly anions with hydrogen is regulated by temperature. Deeply reduced heteropoly anions (at 300°C) are slowly oxidized with oxygen with structure and composition regeneration. The states of molybdenum and vanadium on the surface of samples with coprecipitated platinum Pt_0.1-Cs_2.5H_0.5PMo₁₂O₄₀ (1) and Pt_0.1-Cs_2.5H_2.5PMo₁₀V₂O₄₀ (2), which were studied using XPS, correspond to reduced or reoxidized heteropoly anions in the bulk. Platinum metal particles of ～5 nm in size were observed in high-resolution TEM images obtained after the reduction and storage of sample 1 in air. A heteropoly compound forms two texture levels: spherical nanoparticles of 10–20 nm in size are collected in closely packed globules of 100–300 nm in size. Detailed texture studies, which were performed using nitrogen adsorption isotherms, demonstrated texture mobility under the ambient conditions. The cesium salts of the heteropoly acids were tested in the gas-phase oxidation of benzene to phenol with an O₂ + H₂ mixture at 180°. The effect of platinum concentration on the specific catalytic activity in the presence of deeply reduced heteropoly anions was monitored. The samples containing the salt Cs_2.5H_0.5PMo₁₂O₄₀ exhibited the highest activity in the formation of phenol. The introduction of vanadium into the heteropoly anion impaired the catalytic performance of both deeply and slightly reduced samples.     

Dawson结构磷钼钒酸铯催化H_2O_2氧化苯合成苯酚

采用乙醚反萃取方法合成了Dawson结构磷钼钒酸H8P2Mo16V2O62,进而与碳酸铯反应得到Dawson结构磷钼钒酸铯催化剂CsnH8-nP2Mo16V2O62(n=1-5),利用X射线粉末衍射(XRD)、红外(FTIR)以及SEM等对催化剂进行分析,并以H2O2为氧化剂,评价其在苯液相氧化直接羟基化合成苯酚反应中的催化性能,系统的研究了反应时间、催化剂用量、H2O2用量、反应溶剂等反应条件对催化反应的影响。结果表明,合成Cs3H5P2Mo16V2O62在催化反应中表现出优良的催化活性,优化条件下,苯酚收率达到31.0%;催化剂回收方便,可多次重复使用,在反应过程中,催化剂的Dawson结构没有明显变化。     

Highly selective oxidation of amines to imines by Mn2O3 catalyst under eco-friendly conditions

Enhancing the selectivity of imines for the oxidative self-coupling of primary amines was found to be challenging in the heterogeneous catalysis. Three different manganese oxides (M-3, M-4, M-5) were synthesized by controlling the calcination temperature using a simple template-free oxalate route. The prepared manganese oxides were systematically characterized using XRD, N₂ sorption, SEM, TEM, XPS, H₂-TPR techniques. M-4 gave 96.2% selectivity of imine at 100% conversion of benzylamine, which was far more superior than other existing protocols. Mn³⁺/Mn⁴⁺ ratio was found to affect the selectivity of the imines. The probable reaction pathway for amines oxidation catalyzed by manganese oxides was proposed for the first time.     

Hydrocarbon oxidation with an oxygen-hydrogen mixture: Catalytic systems based on the interaction of platinum or palladium with a heteropoly compound

A series of studies of hydrocarbon oxidation by the O₂ + H₂ mixture in the presence of catalytic systems based on Pt or Pd and a heteropoly compound (HPC) is reviewed. The catalytic systems were prepared from Pd(II) complexes with the heteropoly tungstate anions PW₁₁O ₂₉ ^7? and PW₉O ₃₄ ^9? , the complex salt [Pt(NH₃)₄][H₂Mo₁₂O₄₀]₂ · 7H₂O, mixtures of H₂PtCl₄ or H₂PtCl₆ with H_{3 + n} PMo_{12 ? n} V _n O₄₀ (n = 0–3) heteropoly acids, or supported platinum dispersed in HPC solutions. The interaction of metal ions and particles with HPCs in the initial state and after thermal and redox treatments was investigated by NMR, IR spectroscopy, XPS, EXAFS, HREM, and TPR. The catalytic systems were tested in the liquid-phase oxidation of alkanes, cyclohexane, cycloalkenes, benzene, toluene, and phenol with the O₂ + H₂ mixture at low temperatures. Effective supported catalysts based on platinum nanoparticles associated with the redox-active HPCs H₃PMo₁₂O₄₀ and H₄PMo₁₁VO₄₀ were prepared for gas-phase benzene oxidation into phenol. The oxidation mechanism includes the interaction between dioxygen and platinum (or palladium) and the participation of the HPC in the formation of active oxygen species of radical nature.     

Synthesis of magnetic CuFe2O4 nanoparticles as green catalyst for toluene oxidation under solvent-free conditions

A green method was developed for the synthesis of CuFe₂O₄ magnetic nanoparticles using a Neem leave extract. The prepared nanoparticles with an average size of 19.7 nm were used as an effective catalyst for the oxidation of various aryl alkanes in moderate to excellent yields under solvent-free conditions. The catalyst was characterized by powder- XRD, SEM and TEM study. The key advantages of this protocol are simple preparation, a recyclable heterogeneous catalytic system, and benign reaction condition with good to excellent yields with high selectivity toward acid (42–87%).     

Poisoning of a platinum catalyst with thiophene under reforming conditions

Russian Chemical Bulletin -     

石墨相氮化碳负载钒作为多相催化剂用于苯直接氧化制苯酚

苯酚是一种重要的化工原料,目前苯酚的工业生产路线普遍存在工艺流程复杂、苯酚收率低和环境污染严重等问题.为实现苯酚的绿色生产,苯直接氧化制苯酚的合成路线受到各国研究者的广泛关注.在苯直接羟基化反应常用的 N2O, O2和 H2O2三类氧化剂中, N2O由于来源有限,其工业应用受到极大限制;而 O2不易活化,且反应过程中常需还原剂存在,苯酚收率低;相比之下, H2O2作为氧化剂,其唯一副产物是 H2O,而且反应条件温和,因而以 H2O2为氧化剂的苯羟基化反应是最具工业应用前景的苯酚合成路线.然而,由于苯分子中的 C?H键非常稳定,活化能较高,同时产物苯酚的反应活性要高于反应物苯,因此,为实现苯的高效转化,积极探索研究高活性和稳定性的催化剂变得尤为重要.在我们之前的研究中发现,包含大π体系的氧化石墨烯载体有利于具有同样π共轭体系的反应物苯的吸附,进而促进苯的转化,提高反应活性.而石墨相氮化碳(g-C3N4)具有与氧化石墨烯类似的π共轭体系,且表面具有大量的活性位点和缺陷位,对苯环类物质具有较好的活化作用,这使其可能成为更优异的载体材料.基于此,以 g-C3N4为载体,采用浸渍法制备了一系列不同钒含量的催化剂xV/g-C3N4,并通过 XRD, FT-IR, TEM, TG等表征技术对催化剂进行了系统研究,以期揭示催化剂结构与反应活性之间的构效关系. XRD的表征结果表明,xV/g-C3N4仍具有载体 g-C3N4的层状堆积结构,且该结构不受钒负载量变化的影响.同时, xV/g-C3N4中钒物种的分散度较高,未发生团聚晶化.更直观地,通过 TEM观察发现,xV/g-C3N4中的钒物种均匀分散. FT-IR的表征结果说明钒物种与 g-C3N4之间存在较强的相互作用.此外,通过 TG表征发现, g-C3N4高温稳定性较好,即使焙烧温度高达550°C,其结构仍不受影响.综上所述,在xV/g-C3N4催化剂中,载体 g-C3N4的结构非常稳定,经负载钒物种以及焙烧处理后仍能保持不变;而钒物种与 g-C3N4之间存在较强的相互作用,且均匀分散,使催化剂具有较高的稳定性和较好的催化性能.在以 H2O2为氧化剂,80 wt%醋酸溶液为溶剂的苯直接氧化制苯酚反应中,xV/g-C3N4催化剂显示了良好的催化活性,其中反应活性最高的是8V/g-C3N4催化剂,在最佳反应条件下,苯酚的收率和选择性分别达到24.4%和99.2%.同时,通过计算 TOF值发现,8V/g-C3N4的 TOF值高达13.1 h-1,远高于文献中报道的以 C3N4为载体的催化剂的 TOF值(0.52–0.59 h-1),这表明xV/g-C3N4催化剂具有优异的催化活性.此外,以8V/g-C3N4为代表又进一步考察了催化剂的稳定性,在回收重复实验中催化剂的活性保持稳定.     

Effect of supports for the direct oxidation of benzene to phenol over supported FeCl3 catalyst

The effect of supports on oxidation of benzene to phenol with hydrogen peroxide as an oxidant was tested by using supported FeCl₃ as catalysts. Their activities were affected by acid-base properties of supports. Silica gel which gave strong acid site near the active site had the highest activity among the investigated supports. Several kinds of silica gel which had different pore sizes were used. The maximum activity was obtained at the pore size of 3.5 nm and the reason was discussed.     

Mechanisms for the Ni-mediated oxidation of benzene to phenol by N2O

The gas-phase Ni⁺-mediated benzene oxidation by N₂O on both quartet and doublet potential energy surfaces are surveyed using density functional theory (DFT). Geometries and energies for all relevant intermediates are calculated. The initial N₂O reduction for forming NiO⁺ takes place only via reaction with the excited Ni⁺(⁴F) through the N–O insertion mechanism. The second step of the oxidation can involve two mechanisms: ‘nonradical’ through benzene H migration following the formation of the boat complex of benzene–NiO⁺ or ‘oxygen-insertion’ via rearrangement to an arenium intermediate from the chair-type benzene–NiO⁺ encounter complex. Both mechanisms are energetically available.     

温和条件下Au/HY催化剂催化氧化丙三醇制丙醇二酸

研究了不同载体负载的Au催化剂催化丙三醇水相选择性氧化制丙醇二酸.与Au/CeO2,Au/AC,Au/REY和Au/NaY催化剂相比,Au/HY上获得了高收率的丙醇二酸.在60°C和0.3 MPa氧气压力下,丙三醇转化率达98%,丙醇二酸收率为80%.表征结果表明,小尺寸的Au纳米颗粒对生成丙醇二酸有明显促进作用;反应过程中丙三醇先被催化氧化生成甘油酸,再被进一步氧化生成丙醇二酸.     

An efficient catalyst for ring opening of epoxides with phenol and thiophenol under solvent-free conditions

An efficient and rapid procedure for ring opening reaction of various epoxides with phenol and thiophenol derivatives was developed. The procedure can be obtained at room temperature under solvent-free condition in presence of (C₄H₁₂N₂)₂[BiCl₆]Cl·H₂O (1 mol %). This catalyst can be reused several times without significant loss of activity.     

不同条件下苯与丙烯烷基化反应的催化剂失活研究

对不同条件下苯与丙烯烷基化反应Hβ催化剂的寿命、失活催化剂的积炭量和积炭性质进行了研究。在5.7MPa下,随反应温度变化,反应介质在反应过程中所经历的相态变化不同,导致催化剂的寿命、失活催化剂的积炭量和积炭的性质也存在着较大差异。300℃时,反应介质处于接近于体系临界点的超临界相或高压液相状态,催化剂寿命最长,积炭量大。失活催化剂积炭的元素分析及TPO-MS表征结果发现,积炭的碳氢比与反应温度有关,温度越高,碳氢比越高;而积炭的脱炭温度与反应时间（催化剂寿命）相关,催化剂寿命越长,相应的脱炭温度也越高。     

V2O5/C catalyst for liquid phase oxidation of glyoxal to glyoxylic acid

Science China Chemistry - A study of the catalytic activity of V2O5/C catalyst for the oxygen oxidation of glyoxal has been made, showing that glyoxylic acid can be formed without control of pH...     

甲醛还原Pt/TiO2催化剂用于温和条件下高效催化氧化甲醛

通过浸渍法(IM)和沉积-沉淀(DP)法制备了一系列Pt/TiO2(P25)催化剂,并分别用甲醛溶液和氢气还原处理催化剂.利用原位红外监测催化剂表面吸附物种在反应过程中的变化,探究了催化剂制备和还原条件及Pt负载量对催化剂结构和催化氧化甲醛活性的影响.结果显示,用DP法制备并用甲醛还原的Pt/P25催化剂中Pt颗粒分散均匀,并具有合适的粒径和高浓度的表面活性氧,显示出良好的甲醛氧化活性.在空速30000 ml/(g·h)、反应温度30°C和甲醛初始浓度50 mg/m3的条件下,0.4%Pt/P25(DP-HCHO)上的甲醛转化率达到98%,并能稳定运行100 h以上.相比之下, Pt/P25(DP-H2)由于表面活性氧较少,不利于甲酸盐氧化,活性较低. Pt/P25(IM-H2)虽然具有高浓度的表面活性氧,却同时具有最大的Pt颗粒粒径,在甲醛转化为甲酸盐和甲酸盐氧化两步反应中的活性均较差,因而甲醛氧化活性最差.     

甲醛还原Pt/TiO2催化剂用于温和条件下高效催化氧化甲醛

通过浸渍法(IM)和沉积-沉淀(DP)法制备了一系列Pt/TiO2(P25)催化剂,并分别用甲醛溶液和氢气还原处理催化剂.利用原位红外监测催化剂表面吸附物种在反应过程中的变化,探究了催化剂制备和还原条件及Pt负载量对催化剂结构和催化氧化甲醛活性的影响.结果显示,用DP法制备并用甲醛还原的Pt/P25催化剂中Pt颗粒分散均匀,并具有合适的粒径和高浓度的表面活性氧,显示出良好的甲醛氧化活性.在空速30000 ml/(g·h)、反应温度30°C和甲醛初始浓度50 mg/m3的条件下,0.4%Pt/P25(DP-HCHO)上的甲醛转化率达到98%,并能稳定运行100 h以上.相比之下, Pt/P25(DP-H2)由于表面活性氧较少,不利于甲酸盐氧化,活性较低. Pt/P25(IM-H2)虽然具有高浓度的表面活性氧,却同时具有最大的Pt颗粒粒径,在甲醛转化为甲酸盐和甲酸盐氧化两步反应中的活性均较差,因而甲醛氧化活性最差.     

gamma-1,2-H2SiV2W10O40] immobilized on surface-modified SiO2 as a heterogeneous catalyst for liquid-phase oxidation with H2O2

An organic-inorganic hybrid support has been synthesized by covalently anchoring an N-octyldihydroimidazolium cation fragment onto SiO2 (denoted as 1-SiO2). This modified support was characterized by solid-state 13C, 29Si, and 31P NMR spectroscopy, IR spectroscopy, and elemental analysis. The results showed that the structure of the dihydroimidazolium skeleton is preserved on the surface of SiO2. The modified support can act as a good anion exchanger, which allows the catalytically active polyoxometalate anion [gamma-1,2-H2SiV2W10O40]4- (I) to be immobilized onto the support by a stoichiometric anion exchange (denoted as I/1-SiO2). The structure of anion I is preserved after the anion exchange, as confirmed by IR and 51V NMR spectroscopy. The catalytic performance for the oxidation of olefins and sulfides, with hydrogen peroxide (only one equivalent with respect to substrate) as the sole oxidant, was investigated with I/1-SiO2. This supported catalyst shows a high stereospecificity, diastereoselectivity, regioselectivity, and a high efficiency of hydrogen peroxide utilization for the oxidation of various olefins and sulfides without any loss of the intrinsic catalytic nature of the corresponding homogeneous analogue of I (i.e., the tetra-n-butylammonium salt of I, TBA-I), although the rates decreased to about half that with TBA-I. The oxidation can be stopped immediately by removal of the solid catalyst, and vanadium and tungsten species can hardly be found in the filtrate after removal of the catalyst. These results rule out any contribution to the observed catalysis from vanadium and tungsten species that leach into the reaction solution, which means that the observed catalysis is truly heterogeneous in nature. In addition, the catalyst is reusable for both epoxidation and sulfoxidation without any loss of catalytic performance.