分子围栏催化剂用于甲烷低温氧化制甲醇

《Science》杂志最近刊发了浙江大学肖丰收团队关于甲烷低温选择性氧化研究的重要进展. 基于分子围栏的概念, 作者构筑了一种具有疏水壳层结构的沸石分子筛封装金属纳米粒子, 利用原位生成的过氧化氢氧化甲烷制备甲醇. 他们报道在甲烷的转化率高达17.3%的同时保持了92%的甲醇选择性, 基于金属含量的甲醇产率高达91.6 mmol· {{\mathrm{g}}_{\mathrm{AuPd}}}^{-1} ·h ^-1.     

Au-Pd supported nanocrystals prepared by a sol immobilisation technique as catalysts for selective chemical synthesis

Catalysis by gold and gold-palladium nanoparticles has attracted significant research attention in recent years. These nanocrystalline materials have been found to be highly effective for selective and total oxidation, but in most cases the catalysts are prepared using precipitation or impregnation. We report the preparation of Au-Pd nanocrystalline catalysts supported on carbon prepared via a sol-immobilisation technique and these have been compared with Au-Pd catalysts prepared via impregnation. The catalysts have been evaluated for two selective chemical syntheses, namely, oxidation of benzyl alcohol and the direct synthesis of hydrogen peroxide. The catalysts have been structurally characterised using a combination of scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts prepared using the sol immobilisation technique show higher activity when compared with catalysts prepared by impregnation as they are more active for both hydrogen peroxide synthesis and hydrogenation, and also for benzyl alcohol oxidation. The method facilitates the use of much lower metal concentrations which is a key feature in catalyst design, particularly for the synthesis of hydrogen peroxide.     

单原子催化甲烷直接转化的研究进展

将甲烷直接转化(DMC)为高附加值化学品(如甲醇等化合物),是实现天然气高效利用的有效途径.因甲烷结构非常稳定,使其在温和条件下(反应温度≤150℃的非强酸介质体系)的高效活化极具挑战性.近年来,单原子催化剂(SACs)因其活性物种的高利用率和高选择性,已引起国内外研究者的广泛关注,并被尝试应用于多种反应.研究表明, SACs在DMC反应中表现出独特的催化性能.本综述中,我们总结了在温和条件下, SACs在DMC反应中的研究进展,重点针对热催化反应过程的催化剂设计和反应路径研究进行了归纳和分析.此外,还对光催化反应过程中涉及的SACs上的DMC反应进行了分析.最后,对温和条件下实现DMC进行了总结和展望.     

Metal/zirconia catalysts for the synthesis of methanol: characterization by vibrational spectroscopy

The activation of carbon dioxide by catalytic hydrogenation has been studied as a route for methanol synthesis. Metal/zirconia catalysts suitable for this reaction have been prepared by (i) activation of amorphous metal alloys [1] or (ii) coprecipitation of amorphous zirconia and metal oxides [2]. Vibrational spectroscopy has been used to obtain information on the catalytic reaction mechanism, by the in situ identification of adsorbed species and intermediates under reaction conditions.The reverse water-gas shift reaction, producing CO from CO₂ and hydrogen, plays a crucial role in the reaction mechanism. This reduction is shown to proceed via surface formate, adsorbed close to the metal/zirconia interface. Over Pd/ZrO₂ and Ni/ZrO₂, formate is reduced to methane without further observable intermediates. Pivotal intermediates on the route to methanol, as observed on Cu/ZrO₂ catalysts, are -bound formaldehyde and surface methylate. Addition of silver as a promoter can result in enhanced selectivities and productivities for methanol formation. The synergy between the two metals becomes evident from the spectroscopic measurements; the most prominent feature of the silver-promoted catalysts is a high concentration of surface formaldehyde, which is either preferentially formed or stabilized by the silver component.     

石墨烯负载的金属氧化物纳米颗粒的可控制备及催化性能

采用直接浸渍法、过氧化氢均相氧化沉积法和氨水催化水解法制备了石墨烯负载的铁、钴、镍金属氧化物纳米颗粒.研究了三种沉积方法对颗粒尺寸分布的影响;采用透射电子显微镜、傅里叶变换红外光谱、X射线衍射和X射线光电子能谱表征了催化剂的形貌与结构.用过氧化氢均相氧化沉淀法可制得粒径分布最均匀的纳米颗粒.过氧化氢的氧化作用可使石墨烯表面的氧化基团含量最大化,为纳米颗粒提供了足够的吸附与成核点.氨水加速了金属离子的水解与成核,导致纳米颗粒的粒径增大与不均.以苯甲醇氧化为探针反应考察了催化剂的性能.催化剂的活性按以下顺序逐渐下降:过氧化氢辅助沉积法>直接浸渍法>氨水催化水解法,与纳米颗粒尺寸增长趋势一致.纳米催化剂颗粒尺寸与其活性的良好关联性显示,发展石墨烯负载尺寸可控的纳米催化剂的方法具有重要意义.     

Oxidation of organic compounds by hydrogen peroxide using polymer-anchored azo-metal catalysts

Polymer-anchored azo complexes of Cu(II) and Ni(II) were synthesized by the reaction of chloromethylated polystyrene, 3-aminophenol, and 1-nitroso-2-naphthol with the metal chlorides. The catalytic activities of these complexes were studied in the oxidation of various organic substrates including alkenes, alcohols, alkanes, and sulfides with 30 % aqueous hydrogen peroxide. The structures of both catalysts have been investigated by physiochemical methods. Both catalysts proved to be very stable and could be reused more than five times without significant loss of activity. Furthermore, these catalysts require very mild reaction conditions.     

碳质与金属催化剂热催化裂解甲烷产氢研究进展

甲烷裂解制氢方法具有产氢纯度高和清洁无污染的特点,被认为是当前最有前景的制氢方法之一.现阶段甲烷裂解制氢的研究工作主要集中于制备活性与稳定性兼备的催化剂.我们综述了近年来甲烷裂解制氢反应中碳质催化剂和金属催化剂两大系列催化剂的研究进展,从载体、活性组分、助剂3个方法对目前催化剂裂解甲烷产氢性能的影响进行了系统分析,总结了反应机理和催化剂的失活与再生情况,在以上基础上对催化剂未来的发展趋势进行了展望.     

Efficient Catalytic Production of Hydrogen Peroxide Using Tin-containing Zeolite Fixed Palladium Nanoparticles with Oxidation Resistance

The metal surfaces tend to be oxidized in air through dissociation of the O−O bond of oxygen to reduce the performances in various fields. Although several ligand modification routes have alleviated the oxidation of bulky metal surfaces, it is still a challenge for the oxidation resistance of small-size metal nanoparticles. Herein, we fixed the small-size Pd nanoparticles in tin-contained MFI zeolite crystals, where the tin acts as an electron donor to efficiently hinder the oxidation of Pd by weakening the adsorption of molecular oxygen and suppressing the O−O cleavage. This oxidation-resistant Pd catalyst exhibited superior performance in directly synthesizing hydrogen peroxide from hydrogen and oxygen, with the productivity of hydrogen peroxide at ≈10,170 mmol g_Pd⁻¹ h⁻¹, steadily outperforming the catalysts tested previously. This work leads to the hypothesis that tin is an electron donor to realize oxidation-resistant Pd within zeolite crystals for efficient catalysis to overcome the limitation of generally supported Pd catalysts and further motivates the use of oxidation-resistant metal nanoparticles in various fields.     

Epoxidation of alpha,beta-unsaturated ketones using hydrogen peroxide in the presence of basic hydrotalcite catalysts

The basic layered hydrotalcites have been used as catalysts for the epoxidation of alpha,beta-unsaturated ketones in heterogeneous reaction media using hydrogen peroxide as an oxidant. A wide variety of alpha,beta-unsaturated ketones were oxidized to the corresponding epoxyketones in excellent yields under mild reaction conditions. For example, 2-cyclohexen-1-one gave 2,3-epoxycyclohexanone in 91% yield at 40 degrees C for 5 h with high efficiency in hydrogen peroxide. The catalytic activity of the hydrotalcites increased as the basicity of their surfaces increased. In the case of the epoxidation of less reactive substrates, adding a cationic surfactant such as n-dodecyltrimethylammonium bromide (DTMAB) to the above oxidation system accelerated the epoxidation reaction. These hydrotalcite catalysts were easily separated from the reaction mixture and were reusable.     

Metal–Support Cooperative Catalysts for Environmentally Benign Molecular Transformations

Metal–support cooperative catalysts have been developed for sustainable and environmentally benign molecular transformations. The active metal centers and supports in these catalysts could cooperatively activate substrates, resulting in high catalytic performance for liquid‐phase reactions under mild conditions. These catalysts involved hydrotalcite‐supported gold and silver nanoparticles with high catalytic activity for organic reactions such as aerobic oxidation, oxidative carbonylation, and chemoselective reduction of epoxides to alkenes and nitrostyrenes to aminostyrenes using alcohols and CO/H₂O as reducing reagents. This high catalytic performance was due to cooperative catalysis between the metal nanoparticles and basic sites of the hydrotalcite support. To increase the metal–support cooperative effect, core–shell nanostructured catalysts consisting of gold or silver nanoparticles in the core and ceria supports in the shell were designed. These core–shell nanocomposite catalysts were effective for the chemoselective hydrogenation of nitrostyrenes to aminostyrenes, unsaturated aldehydes to allyl alcohols, and alkynes to alkenes using H₂ as a clean reductant. In addition, these solid catalysts could be recovered easily from the reaction mixture by simple filtration, and were reusable with high catalytic activity.     

甲烷部分氧化制合成气 Ⅰ．甲烷在过渡金属上的活化

文中用同位素交换（Ｄ_２─ＣＨ_４）反应来测量四种过渡金属负载型催化剂对甲烷的活化能力，并与Ｓｖｅｎｓｓｏｎ等从头算的计算结果作了比较，表明最有效活化甲烷分子的Ｃ─Ｈ键的金属是铑（Ｒｈ）．文中还测定了在甲烷部分氧化制合成气反应中，四个不同催化剂的催化活性与选择性，并与它们对甲烷的活化能力进行对比，可以看出甲烷部分氧化反应中，反应活性高的催化剂有效地活化甲烷，断裂Ｃ─Ｈ键，而且氘代甲烷产物分布以形成ＣＤ_４产物为主要成份．     

Selective Styrene Oxidation to Benzaldehyde over Recently Developed Heterogeneous Catalysts

The selective oxidation of styrene under heterogeneous catalyzed conditions delivers environmentally friendly paths for the production of benzaldehyde, an important intermediate for the synthesis of several products. The present review explores heterogeneous catalysts for styrene oxidation using a variety of metal catalysts over the last decade. The use of several classes of supports is discussed, including metal–organic frameworks, zeolites, carbon materials and silicas, among others. The studied catalytic systems propose as most used oxidants tert-butyl hydroperoxide, and hydrogen peroxide and mild reaction conditions. The reaction mechanism proceeds through the generation of an intermediate reactive metal–oxygen species by catalyst-oxidant interactions. Overall, most of the studies highlight the synergetic effects among the metal and support for the activity and selectivity enhancement.     

甲烷部分氧化制合成气Ⅰ．催化剂设计

在已有的关于甲烷催化部分氧化和催化氧化资料的基础上，假设了一个甲烷部分氧化反应的机理，并据此提出了催化剂设计的原则．在分析了Ｏ２，ＣＯ和Ｈ２等在金属表面上的吸附热的基础上，得出如下结论：金属Ｎｉ，Ｐｔ，Ｐｄ，Ｒｈ，Ｒｕ和Ｉｒ可作为甲烷部分氧化催化剂的主要组分，Ｃｕ将是最佳助剂，具有较好的氢溢流功能的Ａｌ２Ｏ３可作为最佳载体     

Oxidative Rearrangement of Isatins with Arylamines Using H2O2 as Oxidant: A Facile Synthesis of Quinazoline‐2,4‐diones and Evaluation of Their Antibacterial Activity

A green and highly efficient synthetic method for the synthesis of quinazoline‐2,4‐diones with hydrogen peroxide as the terminal oxidant has been developed. The reaction features the mild reaction conditions, broad substrate scope, metal‐free catalysts, and sole byproduct water. A plausible mechanism for this process was proposed. Moreover, an antibacterial activity study was performed to evaluate the antimicrobial activities towards two Gram‐negative bacterial strains (Escherichia coli , and Klebsiella pneumonia ) and two Gram‐positive bacterial strains (Staphylococcus epidermidis , and Staphylococcus aureus ) using the Broth microdilution method.     

甲烷直接催化氧化制备甲醇近期研究进展北大核心CSCD

甲烷合成甲醇的方法包括间接法和直接催化氧化(DMTM)法,但是间接法对设备要求高,且甲烷转化率与甲醇选择性均不理想,DMTM法可通过一步反应高选择性制备甲醇,有巨大的应用潜力。对于甲烷DMTM法合成甲醇,均相催化体系通常需要特殊反应介质与贵金属催化剂相结合,虽然反应效率高,但对反应设备有腐蚀性,产物不易分离,应用前景差。液相-异相催化一般使用H_(2)O_(2)作为氧化剂,Au、Pd、Fe和Cu等金属元素作为催化剂主要活性组分,·OH是主要的氧化活性物,可在低温下实现甲烷的活化氧化。因此,异相催化体系是目前研究的主流。气相-异相催化主要使用O_(2)和N_(2)O为氧化剂,前者氧化性更强,后者对于产品选择性更好,此外,厌氧体系中H_(2)O也可直接作为氧供体,常用Cu、Fe、Rh等元素作为催化剂。沸石分子筛是使用最广泛的载体,金属氧化物、金属有机骨架化合物(MOFs)和石墨烯也均有涉及,多金属协同催化已经取得了很好的效果。本文主要总结与概述了热催化甲烷直接催化氧化制备甲醇的近年相关研究,并对今后的研究方向做出了展望。     

Recent advances in the application of nanocatalysts in C-N coupling reactions

The development of various methodologies for the formation of carbon-nitrogen bonds is one of the valuable tasks in the field of organic synthesis because the final products are extensively utilized in pharmaceuticals, biologically active compounds, and natural products. The utilization of nanosized metal catalysts with high surface energy, large surface-to-volume ratio, excellent thermal stability, and reactive morphology in C-N cross-coupling reactions has received considerable attention, in recent years. The excellent catalytic performance, the high yield of products, carrying out the reactions under relatively mild and ligand-free conditions, and less toxicity to the environment, recoverability, and reusability of catalysts for several times without a remarkable degradation in activity are advantages of these nanocatalysts. This review intends to summarize the latest progress in the fabrication of nanocatalysts and their applications in the construction of carbon-nitrogen bonds via cross-coupling reactions. Abundant nanocatalysts based on metal and metal oxide nanoparticles/complexes including copper, palladium, nickel, cobalt, silver, gold, zirconium, and zinc have successfully been applied in these reactions. Various aspects of the reactions, different strategies of fabrication of nanocatalysts, and their recyclability have been surveyed. Literature has been investigated from 2015 to 2021.     

室温下钯-金属酞菁/分子筛复合催化剂催化甲烷选择氧化制甲醇

 在交换了 Fe2+, Co2+或 Cu2+的 Y 型分子筛上, 采用苯酐-尿素固相合成法制备了组装在 Y 型分子筛超笼中的金属酞菁类催化剂. 以 H2O2 为氧化剂, 考察了该金属酞菁/分子筛复合物上甲烷选择氧化制甲醇反应的性能, 并优化了反应条件. 结果表明, 在室温下, 金属酞菁/分子筛复合催化剂 FePc/Y, CoPc/Y 和 CuPc/Y 对 H2O2 氧化甲烷反应均有催化作用. 在这些复合物上进一步担载可催化 H2O2 原位生成的 Pd, Au 或 PdAu 贵金属, 并考察了其催化分子氧选择氧化甲烷反应的性能. 贵金属与金属酞菁/分子筛复合催化剂的偶合实现了室温下分子氧对甲烷的活化. 其中, Pd 与 CuPc/Y 间的协同效应使得室温下甲烷选择氧化反应活性有了较大提高.     

Hydrogen-Deuterium Isotope Exchange of Methane via Non-redox Palladium Catalysis

Under mild conditions, Pd(II) catalysts coordinated to tridentate NHC-amidate-ether ligand successfully activated the carbon-hydrogen bond to facilitate the hydrogen/deuterium isotope exchange on methane. The structural features and catalytic behavior suggested an intriguing non-redox catalytic system derived from the amidate nitrogen. As the amidate nitrogen acts as an internal base, the metal center was able to maintain the oxidation state throughout the reaction. Accordingly, the catalytic system demonstrated its reactivity and stability during the H/D exchange on methane resulting in a high degree of deuterium conversions (44 %) and turnover number (346) under low temperature conditions.     

Recent topics of transfer hydrogenation

A number of transition metal catalysts have been developed for transfer hydrogenation of organic molecules. This method provides a useful process for the reduction of unsaturated molecules without the need for explosive hydrogen gas. An important development in this area is the design of new ligands that improve activity and selectivity under mild reaction conditions. Polydentate ligands are good candidates for producing high performance metal catalysts. This digest describes recent developments in transfer hydrogenation as well as asymmetric reactions using metal catalysts containing polydentate ligand systems.     

过氧化氢直接氧化苯制备苯酚的多相催化研究进展*

作为一种绿色、洁净的氧化剂,使用过氧化氢直接氧化苯来制备苯酚的过程极具吸引力。综述了分子筛、碳基材料、金属氧化物、金属有机框架等多相催化剂在氧化苯制备苯酚反应中的应用,主要讨论了催化剂的合成路线、反应机理和催化性能,希望能为新的多相催化体系的合理设计提供有益的视角。