在过渡金属催化剂上的C―C键断裂以实现生物质的升级

将当前能源生产和消费结构从过度依赖化石能源转变为高效利用可再生能源,是解决能源危机、实现碳中和的有效途径。生物质是最有前途的可再生能源之一,可以取代化石燃料以获得有价值的有机化合物。近年来,大力利用生物质能已成为一种必然趋势。用于生物质转化的传统热化学催化方法通常需要高温、高压等恶劣条件,甚至还需要外部氢或氧源。相比之下,在相对温和的条件下进行的生物质有机分子电催化转化为生产高价值化学品提供了一种绿色高效的策略。特别是,通过C―C键裂解将生物质衍生的分子转化为高价值的短链化学品至关重要。近年来,大量的研究证明过渡金属(TM)电催化剂由于其丰富的三维电子结构和独特的eg轨道增强了过渡金属-氧之间的共价键合,从而在有机物的C―C键断裂中起着至关重要的作用。此外,TM电催化剂的配位环境或电子结构会影响产物的选择性。毫无疑问,明确的反应活性位点和途径有助于深入理解催化剂结构与反应活性之间的构效关系。然而,TM电催化剂介导的生物质衍生有机分子的C―C键裂解反应用于生物质升级的研究目前尚处于起步阶段,其反应机理和催化反应过程尚不清楚。因此,有必要在原子水平上系统地了解电催化剂在C―C键裂解过程中的作用。在本综述中,我们首先依次介绍了广泛研究的TM电催化剂介导的生物质衍生有机分子(包括甘油、环己醇、木质素和糠醛)的C―C键裂解反应,并给出了一些典型的例子和相应的反应途径。然后,系统回顾了过渡金属化合物催化C―C键裂解的反应机理,揭示了界面行为,并构建了TM电催化剂的结构与裂解反应活性之间的构效关系。最后,我们简要总结了上述内容,并强调了在TM电催化剂上研究C―C键裂解的挑战和展望。我们期望这项工作可以为生物质的可控转化和合理设计C―C键裂解的TM电催化剂提供指导。

Pb^(2＋)促进乙醇氧化C―C键断裂的在线电化学透射红外光谱研究

近些年来,直接乙醇燃料电池(DEFC)凭借其能量密度高、绿色环保、毒性低等诸多优点受到了广泛关注,相关的机理研究重点关注的是如何高效地催化乙醇C―C键的断裂。本文通过建立电化学在线透射红外方法,对碱性体系下Pb^(2+)对Pt催化乙醇氧化反应(EOR)的影响进行了研究。结果发现,在不同温度、催化剂载量和电势条件下,Pb^(2+)的加入都有利于Pt催化EOR活性的提高,同时能够提高乙醇氧化电流的稳定性。我们利用电化学在线透射红外光谱(ETIRS)方法对Pt催化EOR的反应产物进行了检测,发现Pb^(2+)存在时产物碳酸根的电流效率明显高于Pb^(2+)不存在时的结果,这一结果说明了Pb^(2+)存在下Pt催化EOR中C―C键断裂比例的提高可能是反应活性提高的重要原因。

生物质转化中C―O/C―C键的活化断裂

生物质作为自然界中唯一可持续的有机碳来源,在解决环境和能源问题、创建一个碳中和的社会方面展现出巨大的潜力。木质生物质是由具有C―O/C―C键的基本结构单元构成的高分子化合物,活化、断裂这些C―O/C―C键是生物质高值化利用的关键,因此在过去十年中受到了广泛的关注。本文首先简要综述了生物质转化中C―O/C―C键催化断裂的现状,主要关注C―O/C―C键断裂的关键挑战和现有策略。我们的目标不是全面概述C―O/C―C键活化断裂的现况,而是提出与C―O/C―C键断裂相关的核心问题并且对未来的研究作出展望。我们选择了碳水化合物和木质素中几种具有代表性的C―O/C―C键来讨论它们在不同情况下协同催化断裂的机理,然后对未来的研究提出自己的见解。

Engineering the coordination structure of Cu for enhanced photocatalytic production of C_(1) chemicals from glucose

Photocatalytic decomposition of sugars is a promising way of providing H_(2),CO,and HCOOH as sus-tainable energy vectors.However,the production of C_(1) chemicals requires the cleavage of robust C−C bonds in sugars with concurrent production of H_(2),which remains challenging.Here,the photo-catalytic activity for glucose decomposition to HCOOH,CO(C_(1) chemicals),and H_(2) on Cu/TiO_(2)was enhanced by nitrogen doping.Owing to nitrogen doping,atomically dispersed and stable Cu sites resistant to light irradiation are formed on Cu/TiO_(2).The electronic interaction between Cu and nitrogen ions originates valence band structure and defect levels composed of N 2p orbit,distinct from undoped Cu/TiO_(2).Therefore,the lifetime of charge carriers is prolonged,resulting in the pro-duction of C_(1) chemicals and H_(2) with productivities 1.7 and 2.1 folds that of Cu/TiO_(2).This work pro-vides a strategy to design coordinatively stable Cu ions for photocatalytic biomass conversion.

Hydrogen auto-transfer under aerobic oxidative conditions: Efficient synthesis of saturated ketones by aerobic C-C cross-coupling of primary and secondary alcohols catalyzed by a Au_6Pd/resin catalyst

Au and Au-containing bimetallic nanoparticles are promising catalysts for the green synthesis of fine chemicals. Here, we used a Au6Pd/resin catalyst for the aerobic C-C cross-coupling of primary and secondary alcohols to produce higher ketones under mild conditions. This is of importance to the construction of a C-C bond. Various substrates were used in the reaction system, and moderate to good yields were obtained. The catalysts can be reused at least five times without decrease of yield. The control experiment and XAFS characterization results showed that hydrogen au- to-transfer occurred on metallic Pd sites even under oxidative conditions. On alloying with Au, the Pd sites became resistant to oxidation and readily abstracted the β-H of the alcohols and transferred the hydride to the C=C bond in the reaction intermediate to give the saturated product.

Production of bio-ethanol by consecutive hydrogenolysis of corn-stalk cellulose

Current bio-ethanol production entails the enzymatic depolymerization of cellulose,but this process shows low efficiency and poor economy.In this work,we developed a consecutive aqueous hydrogenolysis process for the conversion of corn-stalk cellulose to produce a relatively high concentration of bio-ethanol(6.1 wt%)without humin formation.A high yield of cellulose(ca.50 wt%)is extracted from corn stalk using a green solvent(80 wt%1,4-butanediol)without destroying the structure of the lignin.The first hydrothermal hydrogenolysis step uses a Ni–WO_(x)/SiO_(2)catalyst to convert the high cumulative concentration of cellulose(30 wt%)into a polyol mixture with a 56.5 C%yield of ethylene glycol(EG).The original polyol mixture is then subjected to subsequent selective aqueous-phase hydrogenolysis of the C–O bond to produce bioethanol(75%conversion,84 C%selectivity)over the modified hydrothermally stable Cu catalysts.The added Ni component favors the good dispersion of Cu nanoparticles,and the incorporated Au3+helps to stabilize the active Cu^(0)-Cu^(+)species.This multi-functional catalytic process provides an economically competitive route for the production of cellulosic ethanol from raw lignocellulose.

Photocatalytic conversion of waste plastics to low carbon number organic products

As a great threat to all livings on earth,waste artificial plastics now are everywhere,from oceans to our cells[1].The world cannot withstand the growing waste plastic in million tonnes every year,which has already caused environmental pollution and economic losses[2].Besides the efforts for preparing novel plastics with the self‐decomposition ability,methods are needed to clear away these waste plastics leftover from history or recycle well this organic carbon resource[3].Photocatalysis is a potential solution for the conversion of waste plastics under mild conditions.In this perspective,we highlight the effect of photocatalytic approaches toward the generation of low carbon number organic products(C_(n) products,n≤8)from waste plastics,which can proceed under an inert or aerobic atmosphere.Notably,critical analysis of the carbon source in products is necessary to reveal the active species for the C–X bonds(X=C,N,and O)cleavage of plastics.Finally,we outline potential avenues for further development of this emerging field to enhance the yield of C_(n)(n≤8)products from waste plastics.

Efficient splitting of alcohols into hydrogen and C–C coupled products over ultrathin Ni‐doped ZnIn_(2)S_(4) nanosheet photocatalyst

Integrating selective organic synthesis with hydrogen(H_(2))evolution in one photocatalytic redox reaction system sheds light on the underlying approach for concurrent employment of photogenerated electrons and holes towards efficient production of solar fuels and chemicals.In this work,a facile one‐pot oil bath method has been proposed to fabricate a noble metal‐free ultrathin Ni‐doped ZnIn_(2)S_(4)(ZIS/Ni)composite nanosheet for effective solar‐driven selective dehydrocoupling of benzyl alcohol into value‐added C–C coupled hydrobenzoin and H_(2) fuel,which exhibits higher performance than pure ZIS nanosheet.The remarkably improved photoredox activity of ZIS/Ni is mainly attributed to the optimized electron structure featuring narrower band gap and suitable energy band position,which facilitates the ability of light harvesting and photoexcited charge carrier separation and transfer.Furthermore,it has been demonstrated that it is feasible to employ ZIS/Ni for various aromatic alcohols dehydrocoupling to the corresponding C–C coupled products.It is expected that this work can stimulate further interest on the establishment of innovative photocatalytic redox platform coupling clean solar fuels synthesis and selective organic conversion in a sustainable manner.

Catalytic cracking mechanisms of tar model compounds

B3LYP/6-31G(d,p) method was used to investigate the catalytic cracking mechanism of biomass tar model compound.Phenol,toluene and benzene were selected as the tar model compounds and CaO was selected as the catalyst.The pathways of tar compound radical absorbed by CaO were determined firstly through comparing enthalpy changes of the absorption,and then Mulliken population changes were analyzed.The results show that the absorption of tar model compound radical and CaO is an exothermic reaction.Formation of C—O—Ca is more easily than that of C—Ca—O and formation of Caromatic—Caromatic—Ca—O is more easily than that of Caromatic—C(O)—Ca—O.The C—C bond Mulliken populations in tar model compound radicals are reduced by 11.9%,10.5% and 15.5% in the case of a hydrogen atom removed,and those are 15.7%,14.3% and 16.3% in the case of two hydrogen atoms removed through the absorption of CaO.Catalytic ability of CaO acting on the tar model compound is in an order of phenol>benzene>toluene.

Ionization and Dissociation of Benzene and Aniline under Deep Ultraviolet Laser Irradiation

We report a study on photo-ionization of benzene and aniline with incidental subsequent dissociation by the customized reflection time-of-flight mass spectrometer utilizing a deep ultraviolet 177.3 nm laser.Highly efficient ionization of benzene is observed with a weak C4H3+fragment formed by undergoing disproportional C-C bond dissociation.In comparison,a major C5H6+·fragment and a minor C6H6+·radical are produced in the ionization of aniline pertaining to the removal of CNH·and NH·radicals,respectively.First-principles calculation is employed to reveal the photo-dissociation pathways of these two molecules having a structural difference of just an amino group.It is demonstrated that hydrogen atom transfer plays an important role in the cleavage of C-C or C-N bonds in benzene and aniline ions.This study is helpful to understand the underlying mechanisms of chemical bond fracture of benzene ring and related aromatic molecules.

Reflux-synthesized bulk and diluted W-Nb-O mixed oxide bronzes for the valorization of short-chain oxygenates aqueous mixtures

This work reports the preparation of bulk and KIT-6-diluted W-Nb-O mixed oxide bronzes by a reflux method. The influence of the incorporation of Nb and a mesoporous silica on the physicochemical features of the catalysts is studied. The addition of Nb favors the formation of single-phase oxide bronze structure, with improved Lewis acidity;while the incorporation of KIT-6 gives rise to well-dispersed mixed metal oxide particles on the diluter. These diluted W-Nb-O catalysts present enhanced surface areas and mesopore volumes. The materials have been tested in the valorization of an aqueous model mixture (acetol/propanal/ethanol/acetic acid/water weight ratio of 5/25/10/30/30), through C-C bond formation reactions. The increase in the Lewis nature of surface acid sites stands as the key point to maximize the total organic yield during the reaction (C5-C10 products). The best catalysts maintain their catalytic behavior after five consecutive uses.

Manganese-Catalyzed Ring-Opening C—C Bond Fluorination of Cyclobutanols

Manganese-catalyzed C—C bond cleavage of cyclobutanols has attracted great attention due to the high abundance and cheap and eco-friendly behaviour.A manganese-catalyzed ring-opening C—C bond fluorination of cyclobutanols is reported.Under mild conditions,the reaction provides a straightforward access to γ-fluorinated ketones using 10 mol% Mn(OAc)_(2) as catalyst and electrophilic fluorination reagent,which was generated in situ from HF·Et 3N and PhIO,as fluorine source.The reaction has an excellent functional-group tolerance and displays a broad substrate scope,affording the corresponding products in 50%~76%yields.

Oxidative cross-coupling: an alternative way for C–C bond formations

Coupling reaction usually refers to the direct C–C bond formation between two carbon fragments.Generally, cross-coupling reactions between nucleophiles and electrophiles have been extensively studied and become the classic model for bond constructions. Another reaction model, bond formation from two nucleophiles through oxidative cross-coupling, has received more and more attention over the past few years. This paper will discuss the concept of oxidative cross-coupling and give an overview of its recent development.

Recent advances in radical-mediated fluorination through C-H and C-C bond cleavage

The C-H and C-C bonds are abundant in organic compounds,yet generally inert in chemical transformations.Therefore,direct functionalization of inert chemical bonds remains challenging.The fluorine-containing compounds are of special interest for their uses in medicinal chemistry.Direct fluorination of C-H and C-C bonds undoubtedly represents one of the most ideal and attractive approaches to incorporate fluorine atom into complex molecules.Herein,we summarize the recent advances in radical-mediated C-H and C-C bond fluorination.Three types of transformations are discussed:(1)direct C-H abstraction/fluorination of alkanes;(2)decarboxylative fluorination of alkyl carboxylic acids;(3)ring-opening fluorination.

A facile access for the C–N bond formation by transition metal-free oxidative coupling of benzylic C–H bonds and amides

Using 2,3-dichloro-5,6-dicyano-p-benzoquinone(DDQ)as the oxidant,we communicate an efficient oxidative C–N coupling of benzylic C–H bonds with amides to afford a series of amination products in good yields.A wide range of functional groups as well as various sulfonamides and carboxamides are well tolerated.Moreover,this reaction involves both the challenging C–H functionalization and C–N bond formation.