Sustainable Oxidative Cleavage of Vegetable Oils into Diacids by Organo-Modified Molybdenum Oxide Heterogeneous Catalysts

Exploiting vegetable oils to produce industrially valuable diacids via an eco‐friendly process requires an efficient and recyclable catalyst. In this work, a novel catalytic system based on organo‐modified molybdenum trioxide was synthesized by a green hydrothermal method in one simple step, using Mo powder as precursor, hydrogen peroxide, and amphiphilic surfactants cetyltrimethylammonium bromide (CTAB) and tetramethylammonium bromide (TMAB) as capping agents. The synthesized materials were first characterized by different techniques including XRD, SEM, TGA, and FT‐IR. Interestingly, various morphologies were obtained depending on the nature of the surfactants and synthetic conditions. The synthesized catalysts were employed in oxidative cleavage of oleic acid, the most abundant unsaturated fatty acid, to produce azelaic and pelargonic acids with a benign oxidant, H₂O₂. Excellent catalytic activities resulting in full conversion of initial oleic acid were obtained, particularly for CTAB‐capped molybdenum oxide (CTAB/Mo molar ratio of 1:3) that gave 83 and 68% yields of production of azelaic and pelargonic acids, respectively. These are the highest yields that have been obtained for this reaction by heterogeneous catalysts up to now. Moreover, the CTAB‐capped catalyst could be conveniently separated from the reaction mixture by simple centrifugation and reused without significant loss of activity up to at least four cycles.     

Selective Hydrolysis of Arabinogalactan into Arabinose and Galactose Over Heterogeneous Catalysts

Abstract  

The application of solid acid catalysts for the production of monomers from hemicelluloses can be one of the key steps in developing the concept of an integrated forest biorefinery. Arabinogalactans (AG) are hemicelluloses which can be extracted on an industrial scale from larch wood species and has a great potential as a sustainable feedstock for bio-based products. Hydrolysis of AG to monomers over acidic heterogeneous catalysts (Smopex-101 and Amberlyst 15) was successfully demonstrated for the first time to selectively produce arabinose as the primary product, followed by the release of galactose without further degradation of the monomers.     

Analytical Electron Microscopy of Heterogeneous Catalysts

Abstract

Conventional transmission electron microscopy (CTEM) is by now a quite well-established technique for the study of heterogeneous catalysts. It is commonly used for the determination of metallic particles shapes and size distribution on various types of carriers [1, 2]. In addition, dark field imaging and diffraction measurements (in selected area or microdiffraction mode) allows advantage to be taken of the diffraction of the electrons in order to identify the active phase on the basis of its crystal structure [3, 4].     

The Study of Heterogeneous Catalysts by High-Resolution Transmission Electron MicroscoDV

Advances in instrumentation have made it possible in recent years to study the microstructure of inorganic materials at atomic resolution using the technique of high-resolution electron microscopy (HREM). Details of instrumentation have been described elsewhere [l], and applications and trends for HREM have recently been reviewed [2]. Although HREM is primarily a technique for studying bulk defects, it is increasingly also being applied in the profile-imaging mode to derive information about surfaces [3]. The high spatial resolution of the electron microscope makes it a valuable tool for the characterization of heterogeneous catalysts. This is evidenced by the growing number of studies wherein electron micrographs are being used to describe the morphology of a particular catalyst. Profile imaging is proving particularly useful in this regard for following changes in surface structure as a function of treatment conditions [4].     

Analytical Electron Microscopy of Heterogeneous Catalysts

Conventional transmission electron microscopy (CTEM) is by now a quite well-established technique for the study of heterogeneous catalysts. It is commonly used for the determination of metallic particles shapes and size distribution on various types of carriers [1, 2]. In addition, dark field imaging and diffraction measurements (in selected area or microdiffraction mode) allows advantage to be taken of the diffraction of the electrons in order to identify the active phase on the basis of its crystal structure [3, 4].     

制备生物柴油的固体催化剂研究进展

生物柴油是一种清洁、可再生能源。对催化油脂酯交换反应制备生物柴油的固体催化剂的研究进展进行综述,分析了各种固体催化剂的特性,并对催化油脂酯交换反应的固体催化剂今后研究方向进行讨论。     

Aminolysis of Styrene Oxide Over Heterogeneous Acidic Catalysts

Silica alumina and silica zirconia mixed oxides are shown to be effective and regioselective catalysts for the aminolysis of styrene oxide under very mild experimental conditions, giving the corresponding primary ??-amino-alcohol in good to excellent yield.     

生物柴油制备中非均相催化剂的研究进展

生物柴油是一种环境友好型可再生能源,而其生产过程中的催化剂是一个关键性问题。综述了近年来新开发研制的非均相催化剂,重点介绍了催化剂的催化效果、催化剂的合成、催化剂与产物的分离及重复使用等情况,并对其优缺点进行了评述。     

Hemicellulose Hydrolysis in the Presence of Heterogeneous Catalysts

A prominent autocatalytic effect in the hydrolysis of hemicelluloses was observed in the presence of heterogeneous cation-exchange catalysts, Amberlyst 15 and Smopex 101. The kinetic models proposed were based on the reactivities of the non-hydrolysed sugar monomer units and the increase of the rate constant as the reaction progresses and the degree of polymerization decreases. General kinetic models were derived and the kinetic parameters, describing the autocatalytic effect, were determined by non-linear regression analysis. The kinetic model explained very well the overall kinetics, as well as the product distribution in the hydrolysis of hemicelluloses.

     

Heterogeneous Catalysts for Halide-Free Carbonylation of Dimethyl Ether

Acidic cesium salts of 12-tungstophosphoric acid promoted with rhodium, Rh/Cs_xH_3-xPW₁₂O₄₀ (1.5x2 and Rh0.1%), were shown to be novel and effective catalysts for halide-free carbonylation of dimethyl ether (DME) to methyl acetate. The catalysts were characterized by chemical analysis, nitrogen adsorption, XRD, SEM, TGA-DTA and IR spectroscopy. Their behavior may be explained by assuming that (1) activation of the C—O bond in the DME molecule and formation of a metal-alkyl bond occurs in the presence of the strong acid sites and (2) these strong acid sites act in conjunction with Rh carbonyl complexes, which are responsible for CO insertion and acetate formation.     

Hemicellulose Hydrolysis in the Presence of Heterogeneous Catalysts

A prominent autocatalytic effect in the hydrolysis of hemicelluloses was observed in the presence of heterogeneous cation-exchange catalysts, Amberlyst 15 and Smopex 101. The kinetic models proposed were based on the reactivities of the non-hydrolysed sugar monomer units and the increase of the rate constant as the reaction progresses and the degree of polymerization decreases. General kinetic models were derived and the kinetic parameters, describing the autocatalytic effect, were determined by non-linear regression analysis. The kinetic model explained very well the overall kinetics, as well as the product distribution in the hydrolysis of hemicelluloses.     

负载型金催化剂在多相催化中的应用

文章综述了近年负载型金催化剂在环境保护及化学工业方面的应用研究进展,包括CO的常温催化氧化、卤代有机化合物的消除、氮氧化物的还原、丙烯的选择性氧化和氢氧直接氧化法合成双氧水。     

Unprecedented Reductive Esterification of Carboxylic Acids under Hydrogen by Reusable Heterogeneous Platinum Catalysts

Supported metal catalysts have been tested for an unprecedented reductive dimerization of carboxylic acids to esters under 8 bar hydrogen in solvent‐free conditions. Among various metal‐loaded tin oxide catalysts, platinum‐loaded tin dioxide (Pt/SnO₂) shows the highest ester yield for the reaction of dodecanoic acid. Among Pt catalysts on various supports, Lewis acidic oxides, especially SnO₂, show high activity. The most active catalyst, 5 wt% Pt/SnO₂ reduced at 100 °C, is effective for the reductive esterification of various carboxylic acids, and the catalyst is reusable for nine cycles, demonstrating the first successful example for the title reaction. Infrared (IR) studies of a model compound (formic acid) on some metal oxides indicate a strong Lewis acid‐base interaction between SnO₂ and the carbonyl oxygen. For Pt/SnO₂ catalysts with different Pt particle sizes, the activity increases with decreasing size of Pt metal. A cooperative catalysis of the Pt metal nanoparticles and the Sn⁴⁺ Lewis acid sites is proposed.

     

Aerobic Oxidative Intramolecular Aromatic Coupling via Heterogeneous Metal Catalysts

An aerobic, heterogeneously catalyzed oxidative intramolecular coupling reaction of aromatic compounds is reported here. Using commercially available, recyclable heterogeneous metal catalysts, the coupling reactions of o‐terphenyls and 1,ω‐biarylalkanes proceeded quickly under mild conditions, i.e., at room temperature under oxygen as a co‐oxidant almost all within 1 h, to provide the corresponding coupled products like triphenylenes and phenanthrenes in good to excellent yields. This reaction is an easily handled, practical, and atom‐economical coupling method, which is of great importance in modern organic syntheses.

     

高通量筛选技术在多相催化研究中的应用

通过对组合催化研究的关键因素－－催化剂高通量筛选技术的评价分析认为：在对已有的催化体系和催化剂优化的同时，如何高校研制开发新筛选检测技术，诸如反应器设计和检测器的选择，是组合催化研究的主导思想，对此的深刻理解和运用将增强实验室的创新能力。