Biochar-based functional materials as heterogeneous catalysts for organic reactions

The development of cheap, effective and heterogeneous catalysts remains a substantial challenge in organic synthesis. Of the extensive heterogeneous catalysis, biochar materials have attracted increasing attention to be considered as an important class of support materials in organic reactions due to their distinctive characteristics such as high porosity, large specific surface area, high adsorption ability, excellent cation exchange capacity and outstanding stability. This review highlights recent advances over the past 5 years, outlining the synthetic methods of biochar materials and their applications as catalysts or catalyst supports in a range of organic reactions including oxidation, reduction, esterification, coupling, alkylation and multi-component reactions.     

High-throughput selection for heterogeneous catalysts

A catalyst library of 80 samples with different mass ratios of rare earth elements, cobalt (Co), cerium (Ce), and indium (In), was prepared by impregnation of a fresh HZSM-5 zeolite support. A high-throughput detection setup, based on UV absorption spectroscopy, was developed for heterogeneous catalyst selection. The catalytic properties of the library were tested in the selective catalytic reduction of NO by methane at 673 K. Among the Co/Ce series, the catalyst with Co/Ce = 2:1 and Co/H-ZSM5 = 2.5% has shown remarkable efficiency (up to 78%). In the Ce/In series, the reactivity of the catalyst with the support composition of Ce/In = 1:1 and Ce/H-ZSM5 = 2.0% was < or = 88%. Our initial experiments definitely indicated that this simple and inexpensive multichannel setup can be applied for the selection of other heterogeneous catalysts. According to the variation of the UV light intensity, resulting from the absorption of the reactant or product, it was possible to monitor the relative quantity of reactants or products during a catalytic reaction.     

The formation mechanism of Mo-methylidene species over Mo/HBeta catalysts for heterogeneous olefin metathesis: A density functional theory study

Density Functional Theory (DFT) calculations were performed to optimize the Mo active sites in HBeta zeolite catalysts as well as to locate the reaction pathways to form the Mo-methylidene species. Two different Mo active sites, i.e., the oxidized Mo^VIO₂ and its reduced form Mo^VO(OH), were developed and incorporated into HBeta zeolites by replacing a pair of Brønsted acidic sites. The Mo-methylidene species were found to be produced through two elementary reaction steps, and the Mo-oxametallacyclobutanes were identified as the intermediates. The activation barriers of the decompositions of the oxametallacyclobutane intermediates (Step 2) were estimated to be higher than those of the ethene addition on the Mo active sites (Step 1). The oxidation states of the Mo centers exerted marked influences on the stabilities of the intermediates as well as on the activation barriers and reaction heats of Steps 1 and 2, which were elucidated by the electronic properties of the O_b-ligands directly bonded to the Mo centers. Both free energy barriers and reaction heats have indicated that the whole processes of generating the Mo-methylidene species were preferred over the Mo(VI) rather than Mo(V) active site. Accordingly, the Mo(VI) active site was more efficient in catalyzing the formation of Mo-methylidene species in the heterogeneous Mo/HBeta catalytic systems.     

Self-supported heterogeneous catalysts for enantioselective hydrogenation

"Self-supported" catalysts were prepared by the reaction of bis-MonoPhos ligand with rhodium(I) metallic ion on the basis of molecular assembling through coordination. These polymeric metal-organic assemblies are insoluble in common organic solvents and, as a result, provide an excellent opportunity for running asymmetric catalysis heterogeneously. The application of the self-supported Rh(II) catalysts in the asymmetric hydrogenation of olefin derivatives afforded a variety of enantioenriched amino acid and amine derivatives with high yields and enantioselectivities. This strategy might provide a new direction in asymmetric catalysis, particularly for the development of practical heterogeneous asymmetric synthesis of optically active compounds.     

Simulation of heterogeneous catalysts and catalytic processes using the density functional method

The review is devoted to the use of high-level quantum-chemical calculations by the density functional method for the simulation of heterogeneous catalytic systems based on transition metals. The following problems are considered: (1) the development of methods for simulating metal particles supported on the surfaces of ionic and covalent oxides; (2) the calculation of the properties of individual transition metal atoms and small clusters adsorbed on the surfaces of MgO, α-Al₂O₃, γ-Al₂O₃, and various modifications of SiO₂ and in the pores of zeolites; (3) the mechanisms of hydrogen activation and acrolein hydrogenation on the metallic and partially oxidized surface of silver; and (4) the mechanism of formation of carbon residues upon the decomposition of methanol on nanosized Pd particles.     

Self-supported chiral catalysts for heterogeneous enantioselective reactions

The development of heterogeneous chiral catalysts for enantioselective reactions is highly desirable in order to overcome some drawbacks of homogeneous catalysts. Different from the conventional approaches by using various types of supports or biphasic systems for the recovery and reuse of homogeneous catalysts, a conceptually new strategy for heterogenization of homogeneous chiral catalysts, that is, a "self-supporting" approach, has been developed to use homochiral metal-organic coordination polymers generated by the self-assembly of chiral multitopic ligands with metal ions, and thus obviates the use of any support. In this concept article, the success of this "self-supporting" strategy will be exemplified in heterogeneous catalysis of asymmetric carbonyl-ene, sulfoxidation, epoxidation, and asymmetric hydrogenation reactions.     

Selection of heterogeneous catalysts for acetophenone hydrogenation

The electronic structures of acetophenone species adsorbed on supported mono- and polymetallic catalysts have been calculated by the simple LCAO MO method. A correlation between the catalyst selectivity and the order of the -bond formed upon adsorption has been found, from which the selectivity of several polymetallic catalysts has been predicted and experimentally confirmed.

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l-Menthol as new scaffold for designing chiral phase-transfer catalysts

We herein report, a new class of chiral phase-transfer catalysts derived from l-menthol. The moderately good enantioselectivity exhibited by these catalysts have been explained based on single crystal X-ray data and molecular modelling studies.     

A fluorophore's electron-deficiency does matter in designing high-performance near-infrared fluorescent probes

The applications of most fluorescent probes available for Glutathione S-Transferases (GSTs), including NI3 which we developed recently based on 1,8-naphthalimide (NI), are limited by their short emission wavelengths due to insufficient penetration. To realize imaging at a deeper depth, near-infrared (NIR) fluorescent probes are required. Here we report for the first time the designing of NIR fluorescent probes for GSTs by employing the NIR fluorophore HCy which possesses a higher brightness, hydrophilicity and electron-deficiency relative to NI. Intriguingly, with the same receptor unit, the HCy-based probe is always more reactive towards glutathione than the NI-based one, regardless of the specific chemical structure of the receptor unit. This was proved to result from the higher electron-deficiency of HCy instead of its higher hydrophilicity based on a comprehensive analysis. Further, with caging of the autofluorescence being crucial and more difficult to achieve via photoinduced electron transfer (PET) for a NIR probe, the quenching mechanism of HCy-based probes was proved to be PET for the first time with femtosecond transient absorption and theoretical calculations. Thus, HCy2 and HCy9, which employ receptor units less reactive than the one adopted in NI3, turned out to be the most appropriate NIR probes with high-sensitivity and little nonenzymatic background noise. They were then successfully applied to detecting GST in cells, tissues and tumor xenografts in vivo. Additionally, unlike HCy2 with a broad isoenzyme selectivity, HCy9 is specific for GSTA1-1, which is attributed to its lower reactivity and the higher effectiveness of GSTA1-1 in stabilizing the active intermediate via H-bonds based on docking simulations.

An abnormal and intriguing phenomenon that the fluorophore''s electron-deficiency could affect a probe''s performance is now revealed for the first time.     

铜基非贵金属异相催化剂在环境修复中的应用（英文）

近年来,全球经济和工业高速发展带来的环境问题,不仅严重影响着经济社会的可持续发展,更极大地危害着人类健康.石油化工、医药生产和交通运输等过程产生的气、液、固相污染物可直接或间接造成臭氧层空洞、光化学烟雾及水体污染等重大环境问题.气相污染物中,CO和可挥发性有机物(VOCs)不仅具有生物毒性,更是形成光化学烟雾等大气污染的主要前驱体.NO_x和SO2会造成酸雨的形成,极大地破坏生态系统.工业废水中难分解的有机污染物可对环境造成持续性破坏.而不完全燃烧产生的碳烟颗粒物不仅影响气候和大气环境,同时可导致心血管疾病高发,危害人体健康.源头控制是环境污染治理的关键,而催化净化是当前污染物源头控制最有效的技术之一.因此,设计和开发稳定、高效的环境修复催化剂是科学家们面临的一个关键问题.传统贵金属(Pt,Rh,Pd)催化剂虽然催化活性高,但是存在价格昂贵且易中毒等不足.而过渡金属及其氧化物因具有高活性、价格低廉和高储量等特点有望成为贵金属的替代催化剂.铜是具有3d轨道的过渡金属,有活泼的物理化学性质,是工业中大量应用的有色金属.铜基氧化物因高氧化还原电势和低环境危害被广泛应用于热催化、电催化和光催化.基于文献报道,铜基催化剂主要分为三类:铜氧化物(CuO_x),负载型铜氧化物(CuO_x/support)和固溶体铜氧化物(CuO_x-X).本篇综述首先探讨了铜氧化物的价态、晶体结构、形貌、暴露晶面以及载体与催化剂活性之间的内在联系,阐明铜基催化剂结构与性能的构效关系及高效催化剂的设计原则;继而全面总结了近年来不同类型的铜基材料在催化净化环境污染物中的应用,主要介绍了以下5类反应:CO的催化氧化,NO_x的选择性催化还原(SCR),VOCs的完全燃烧,废水中有机污染物降解,以及碳烟颗粒物催化燃烧.我们深入阐述铜氧化物的催化活性位点和催化机制;分析负载型铜基催化剂的比表面积、分散度、协同作用和界面作用对催化剂的活性和稳定性的影响;阐明固溶体催化剂的独特原子组成设计与性能关系,为高效催化剂设计提供思路.此外,本综述对铜基催化剂在环境催化中的研究现状以及尚未解决的问题进行了剖析与展望.通过铜氧化物表面调控,复合催化剂的界面调控,具有更高稳定性和抗中毒性的高效催化剂有望开发成功,而团簇及单原子铜催化剂也有望在此领域有所突破.     

Screening heterogeneous catalysts for the pyrolysis of lignin

The pyrolytic conversion of pure lignin at 600 °C in flowing helium over five catalysts is described and compared to the control bed material, sand. Product distribution as char, liquid, and gas are described as well as the composition of the liquid and gas fractions. The catalysts examined were HZSM-5, KZSM-5, Al-MCM-41, solid phosphoric acid, and a hydrotreating catalyst, (Co/Mo/Al₂O₃). The sand yielded a liquid phase that was 97% oxygenated aromatics and a gas phase that was CO (18 vol%), CO₂ (16 vol%), and CH₄ (12 vol%). HZSM-5 was the best catalyst for producing a deoxygenated liquid fraction yielded almost equal amounts of simple aromatics (46.7%) and naphthalenic ring compounds (46.2%). The gas phase over this catalyst consisted of CO (22 vol%), CO₂ (14 vol%), H₂ (12 vol%), and CH₄ (10 vol%). The Co/Mo/Al₂O₃ hydrotreating catalyst yielded a liquid consisting of 21% aromatics, 4% naphthalenics, and 75% oxygenated aromatics and a gas phase that was rich in hydrogen: H₂ (18 vol%), CO₂ (16 vol%), CO (12 vol%), and CH₄ (8 vol%).     

Development of heterogeneous catalysts for transesterification of triglycerides

This paper describes a preliminary work done towards the development of new metallic heterogeneous catalysts to be used in the transesterification reaction of triglycerides, which is of considerable interest in the production of biodiesel. Biodiesel is a mixture of mono-alkyl esters of fatty acids, and is currently manufactured by transesterification of triglycerides with methanol using NaOH or KOH as liquid base catalyst. Catalysts as such are corrosive to the equipment, and as these catalysts are present in the liquid phase, must be neutralized after the completion of the reaction, typically using HCl, thus producing salt streams. Moreover, due to the presence of free fatty acids, it reacts to form soaps as unwanted by-products, hence requiring more expensive separation processes. Therefore, there is a great need for the development of industrial processes for biodiesel production using solid acid catalysts. The key benefit of using solid acid catalysts is that no polluting by-products are formed, and the catalysts do not have to be removed since they do not mix with the biodiesel product.     

A window diagram for key component analysis in on-line gas chromatography

Window diagrams that optimize for the separation of only one or a few components in a complex mixture are applied to on-line process analysis when speed of analysis is more important than a complete separation of all components in the sample. A window diagram based on retention indexes is the most useful for quickly evaluating the feasibility of a given pair of phases. The one with the most useful output is one based on partition ratios, as this can be used directly with the columns in hand. A PC-based spreadsheet program with integral specific retention volume data for the common liquid phases is described as a tool for selecting the optimum ratio of lengths for the columns in hand.     

Cerium-based catalysts for N-oxidation of pyridine-based derivatives: homogeneous and heterogeneous systems

Herein, the catalytic properties of the cerium (IV) salt, cerium (IV)-sandwiched polyoxometalate (POM) and cerium (IV)-sandwiched polyoxometalate intercalated in layered double hydroxides (LDHs) in the H₂O₂-based green oxidation reactions have been evaluated. These cerium (IV)-based systems were applied as homogeneous and heterogeneous catalysts for the oxidation of pyridines. Despite the fact that the cerium (IV)-sandwiched polyoxometalate as a homogeneous reaction system gives good results, there are some disadvantages in recovery and reusability process. To overcome these problems, new nano catalyst was synthesized by intercalation of the Cerium (IV)-sandwiched polyoxometalate into tris(hydroxymethyl) aminomethane-modified layered double hydroxides (Tris-LDH-CO₃). The as-prepared nanocomposite was characterized and used as an effective heterogeneous catalyst for the oxidation of pyridines under mild conditions in the presence of H₂O₂ as an oxidant. The new heterogeneous nanocomposite can be recovered and reused easily from the reaction media at least ten times without significant decrease in catalytic activity.

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用于高性能锂-硫电池的氮化硼纳米片/碳纤维改性隔膜

通过静电纺丝、热亚胺化和碳化过程,将氮化硼纳米片(BNNSs)负载在碳纤维(CFs)表面,组成用于修饰商业聚丙烯(PP)隔膜的氮化硼纳米片/碳复合纤维(BNNSs/CFs)复合材料。BNNSs和CFs的协同作用为电池提供了额外的导电路径,并将可溶性多硫化锂固定在正极区域。结果表明,采用10BNNSs/CFs-PP隔膜的电池在0.05C下的初始放电容量高达1 295.7 mAh·g^-1,当电流密度增加到1C时,以10BNNSs/CFs-PP为隔膜的电池也具有良好的长期循环稳定性,在400次循环后最终容量高达568.1mAh·g^-1,每次循环容量衰减0.073%。     

A microwave-heated infrared reaction cell for the in situ study of heterogeneous catalysts

A transmission infrared microreactor cell which holds a pressed disc in a controlled atmosphere and allows microwave and conventional heating up to 423 K is demonstrated using the oxidation of carbon monoxide over the standard catalyst EUROPT-1. Optical characteristics are determined by the choice of CaF2 as the window material, allowing transmission from 77,000-1000 cm(-1). An oscillating microwave power regime with a peak height of 200 W is used and time-resolved infrared spectra and mass spectrometry show oscillations in the reaction which correspond to the microwave heating.     

用于高性能锂-硫电池的氮化硼纳米片/碳纤维改性隔膜

通过静电纺丝、热亚胺化和碳化过程,将氮化硼纳米片(BNNSs)负载在碳纤维(CFs)表面,组成用于修饰商业聚丙烯(PP)隔膜的氮化硼纳米片/碳复合纤维(BNNSs/CFs)复合材料。BNNSs和CFs的协同作用为电池提供了额外的导电路径,并将可溶性多硫化锂固定在正极区域。结果表明,采用10BNNSs/CFs-PP隔膜的电池在0.05C下的初始放电容量高达1 295.7 mAh·g^-1,当电流密度增加到1C时,以10BNNSs/CFs-PP为隔膜的电池也具有良好的长期循环稳定性,在400次循环后最终容量高达583.1mAh·g^-1,每次循环容量衰减0.069%。     

用于高性能锂-硫电池的氮化硼纳米片/碳纤维改性隔膜

通过静电纺丝、热亚胺化和碳化过程,将氮化硼纳米片(BNNSs)负载在碳纤维(CFs)表面,组成用于修饰商业聚丙烯(PP)隔膜的氮化硼纳米片/碳复合纤维(BNNSs/CFs)复合材料。BNNSs和CFs的协同作用为电池提供了额外的导电路径,并将可溶性多硫化锂固定在正极区域。结果表明,采用10BNNSs/CFs-PP隔膜的电池在0.05C下的初始放电容量高达1 295.7 mAh·g^-1,当电流密度增加到1C时,以10BNNSs/CFs-PP为隔膜的电池也具有良好的长期循环稳定性,在400次循环后最终容量高达568.1mAh·g^-1,每次循环容量衰减0.073%。     

Microencapsulated linear polymers: "soluble" heterogeneous catalysts

A new strategy for supporting catalysts based on the microencapsulation of linear polymers is presented. In this paper, we present a DMAP capsule that is capable of catalyzing acylation reactions. The catalyst is compared to DMAP on cross-linked and linear polystyrene, as well as small molecule DMAP. Rapid optimization through modification of encapsulation conditions is demonstrated. The optimization provides a dynamic range of catalysis from 90 to 300% of the rate of DMAP on polystyrene.     

Design of heterogeneous catalytic systems: New cement-containing catalysts

A procedure for new cement-containing (MO–Al₂O₃, M=Ca, Zn, Ni, Cu) supports, adsorbents and catalysts has been designed.