蒸汽辅助合成STW结构硅锗酸盐分子筛

采用蒸汽辅助法制备了高稳定性STW结构硅锗酸盐分子筛. 相比于传统水热方法, 使用温和的蒸汽辅助可显著减少模板剂用量, 产物结晶度与骨架Si元素含量更高. 利用X射线衍射(XRD)、 扫描电子显微镜(SEM)、 能量散射谱(EDS)、 热重(TG)分析等技术手段考察了蒸汽辅助合成硅锗酸盐分子筛过程中水对产物结构的影响, 发现随着外加水量的增加, 产物从纯相GeO₂逐渐转化为STW分子筛纯相, 最终变为GeO₂, STW与MFI结构的混相; 此外, 反应物中带入的痕量水可以优先活化Ge元素, 从而在一定程度上决定了产物构型.     

具有 MWW 结构钛硅分子筛的研究进展

 综述了具有 MWW 结构钛硅分子筛的制备方法、孔道和晶体结构的调变和修饰以及催化应用三个方面的研究进展. 与 TS-1 相比, 具有 MWW 结构钛硅分子筛的制备方法多种多样; 其孔道结构可塑性强, 通过采用层间剥离、柱撑以及分子水平硅烷化插硅扩孔技术, 可以增大和暴露孔道和外表面, 满足不同选择氧化反应的要求. 由于 MWW 结构钛硅分子筛拥有复杂而独特的孔道结构, 所以在小分子 (如直链烯烃等) 的环氧化反应, 和大分子 (环状烯烃, 二苯并噻吩等) 氧化反应中都表现出优异的催化性能. 此外, 该钛硅分子筛表现出与 TS-1 完全不同的溶剂效应, 用于烯丙基氯液相环氧化与酮类氨氧化反应主产物选择性更高.     

以胆碱为绿色无毒有机结构导向剂合成高硅Y型分子筛

分子筛作为一类重要的无机多孔晶体材料,由于其规整的孔道结构以及优异的酸性质等特点,在催化剂、吸附剂和离子交换床等许多领域有着重要而广泛的应用.而现代分子筛制备方法的发展主要得益于有机结构导向剂(OSDA)在分子筛合成中的广泛使用.但是,大部分OSDA都具有剧毒、价格昂贵、制备方法繁琐等缺点,因而限制了其大规模应用.高硅Y型分子筛的合成研究也面临同样的问题.Y型分子筛具有十二元环孔口和三维孔道结构,是目前催化裂化催化剂中的主要活性组分.目前,通过常规合成方法无法获得硅铝比大于6.0的Y型分子筛,无法满足石油化工对其酸性的要求.目前工业上主要通过后处理法得到高硅Y沸石,但该方法繁杂的后处理过程、不均匀的化学分布、大量损失的结晶度以及严重的环境污染促使人们开发直接合成高硅Y型分子筛的新方法以替代后处理过程.此外,使用OSDA一步法合成的高硅铝比Y型分子筛具有优异的热和水热稳定性.因此,使用OSDA一步直接合成高硅Y型分子筛在材料合成和催化领域一直备受关注.然而,目前尚未见关于绿色OSDA用于高硅Y型分子筛合成的报道.本研究首次将氢氧化胆碱或氯化胆碱作为一种新型、绿色、廉价的OSDA引入到高硅Y分子筛的合成凝胶体系,成功合成了高结晶度且硅铝比大于6.0的高硅Y型分子筛.实验详细考察了合成条件对硅铝比的影响,并采用XRD, XRF, NMR,TG以及N2物理吸附等表征手段研究了合成样品的物理化学性质.表征结果证明,胆碱阳离子作为一个稳定的OSDA存在于分子筛的孔结构中,并且取代了部分Na~+以平衡分子筛骨架的负电荷,因此胆碱的使用可使样品的硅铝比提高并具有更加优异的热稳定性和水热稳定性.实验确定了Na~+和OSDA~+在高硅Y分子筛合成中的竞争关系.大量的实验证据表明, Na~+进料比例对FAU骨架硅铝比有决定性的影响.首次提出采用氢氧根离子型OSDA是一种直接有效提高骨架硅铝比的方法.     

胆碱和*BEA分子筛在硅锗铝IWR分子筛制备中的协同导向效应

分子筛的制备过程一般需要结构导向剂的参与.结构导向剂主要包括碱(土)金属离子、有机胺或季铵盐为代表的有机模板剂和固体晶种等三类.研究合成凝胶中不同结构导向剂之间的作用对于理解分子筛晶化机理意义重大.以往的研究大都集中在模板剂-模板剂、模板剂-碱(土)金属离子和模板剂-同晶之间的相互作用,迄今尚未有模板剂-异晶之间相互作用研究的报道.我们研究组首次发现模板剂和异晶在分子筛制备中存在协同导向效应.在硅锗铝IWR分子筛的合成中,我们考察了不同的季铵碱模板剂和铝源,发现只有使用胆碱作模板剂、*BEA分子筛作铝源才可以成功制得目标分子筛,相同条件下不加入*BEA分子筛或换用MOR、ZSM-5、MCM-22、USY分子筛及异丙醇铝等铝源都无法合成得到IWR分子筛.这说明*BEA分子筛在IWR分子筛的制备中起到了其他铝源所不具备的结构导向作用,因此我们称之为合成IWR分子筛的"异晶".为了研究胆碱和*BEA分子筛之间的相互作用,进而揭示模板剂-异晶协同导向制备分子筛的一般规律与反应机理,我们制备了不同晶化时间的IWR分子筛样品,使用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、紫外-拉曼光谱(UV-Raman)、固体核磁共振(MAS NMR)和N2物理吸附等手段对这些样品进行了表征.结果显示,加热过程中*BEA分子筛首先发生溶解解离, 72 h后该分子筛相完全消失;12 h开始出现CDO分子筛相,随着晶化时间延长, CDO分子筛先增多后减少,在24 h时达到最大值, 120 h时消失,说明该分子筛是晶化过程的一个中间相;IWR分子筛在12 h开始出现,此后结晶度不断升高,至168 h晶化完全.在上述表征的基础上,我们提出了模板剂-异晶协同导向制备IWR分子筛的晶化机理.IWR分子筛的晶化分为以下5个步骤:(1)*BEA分子筛溶解解离得到硅铝4元环、5元环和6元环等结构单元;(2)胆碱诱导形成硅锗5元环结构单元;(3)硅锗5元环组装生成CDO分子筛;(4)CDO分子筛溶解解离形成硅锗5元环;(5)*BEA分子筛导向的结构单元与胆碱导向的结构单元重组生成IWR分子筛.其中,步骤3和4是一对可逆反应,且可与步骤5同时进行;随着反应物原料的不断消耗,步骤5占据主导,从而导致CDO分子筛完全消失和IWR分子筛的结晶完成.由于胆碱只导向生成5元环结构单元,而构成IWR分子筛骨架结构的4元环和6元环只能由*BEA分子筛提供,因而模板剂和异晶在反应中都不可或缺,二者起到协同导向的作用.分析发现,*BEA分子筛与IWR分子筛具有共同的结构单元(4、5、6元环)和一定的结构相似性是其可以成为异晶、发挥协同导向作用的关键.上述协同导向法的关键在于模板剂和异晶分别导向生成部分结构单元,再经重组得到目标分子筛.这种方法有望用于合成通过传统水热法难以得到的分子筛,并且为新结构分子筛的开发提供新思路.使用协同导向法制备更多种类分子筛的研究正在进行中.     

以纯硅silicalite-1为晶种制备空心结构ZSM-5沸石分子筛

微孔分子筛在实际应用过程中常常受到扩散限制的影响,分子筛内部的利用率不高;制备空心结构分子筛对于改善分子筛扩散传质、提高分子筛利用率具有重要意义。以纯硅silicalite-1为晶种,以四丙基氢氧化铵(TPAOH)为结构导向剂制备ZSM-5分子筛;无定型硅铝物种首先在晶种表面晶化生长,同时碱性合成体系的碱度则可以溶解不稳定的silicalite-1晶种,通过控制调变生长与溶解的相对速率制备得到具有空心结构的ZSM-5分子筛;该多级孔道ZSM-5分子筛的制备方法简单、易操作,具有广泛的应用潜力。     

钛硅介孔分子筛

综述了钛硅介孔分子筛的合成、表征及其应用研究进展.评述了钛硅介孔分子筛的合成方法与合成条件对分子筛结构性能、钛物种的配位状态和催化性能的影响.介绍了鉴定钛硅介孔分子筛内骨架钛原子的多种波谱学方法以及钛硅介孔分子筛在选择氧化、光催化、酸催化反应中的应用,并指出钛硅介孔分子筛是一种非常有应用前景的环境友好的多相催化剂.     

超细微MEL结构铜硅分子筛的合成及理化性质

过渡金属杂原子分子筛的合成及其性质表征近年来引起了广泛关注[1～3].将铜离子嵌入分子筛、层柱状材料中作为活性中心,在汽车尾气处理[4]及有机物选择氧化反应[5]中呈现出良好的催化活性,其研究在理论和应用上均具有重要意义.超细微分子筛(粒径小于1×10-7m)具有比普通分子筛更高的比表面积和比活性,在不同领域有特殊的用途,其合成方法一直是分子筛研究工作者探索的热门课题.本文采用“络合物法”[6]首次合成了超细微纳米晶MEL结构铜硅分子筛,并通过XRD,TEM,XRF,FTIR,ESR,TG-DTA及NH3-TPD对其理化性质进行了研究.1　实验部分M…     

微孔-介孔复合结构分子筛的合成及表征研究

以工业现有的ZSM-5作为原料,经一定化学处理的ZSM-5作为部分硅铝源,与介孔分子筛的凝胶在水热条件下进行组装得到具有微孔、介孔双孔分布的复合分子筛,并采用XRD、N2吸附脱附、IR、SEM、TEM等测试手段对合成样品进行分析表征,考察了主要合成条件对分子筛性能的影响.结果表明,合成过程中微孔与介孔结构之间会相互转化,样品中微孔与介孔特征峰存在此消彼长的关系.非临氢反应结果表明,复合分子筛具有较高的异构化选择性.     

基于分子筛模板的银/硅铝无定形结构复合材料的合成及光谱性质

利用硅铝无定形结构作为保护层的银纳米颗粒在杀菌和催化领域具有重要应用. 银纳米颗粒的形貌控制是其优异性能的重要保证, 尤其是具有规则结构的银纳米颗粒的合成一直是该领域的难点. 本文以亚稳态结构的硅铝分子筛作为模板, 在室温条件下采用离子交换方法, 通过调整银离子的含量和离子交换时间, 控制银在分子筛中的分布和含量, 在还原剂N(C₂H₅)₃存在下, 通过微波还原反应获得了不同银/硅铝无定形结构比例的复合材料. 透射电子显微镜测试结果表明, 不同比例的前驱体经微波法还原后, 小尺寸的银纳米颗粒可以分布在无定形的硅铝基质中; 当增大银的比例后, 银纳米颗粒则出现项链式结构, 并且由无定形硅铝薄层链接并包裹. 这类结构既具有银纳米颗粒的催化性能, 同时又在硅铝薄层的保护下表现出良好的稳定性, 在杀菌和催化领域具有广泛的应用前景.     

磷酸硅锌铝分子筛（ZnAPSO—5）的合成,结构及性能研究

以二乙氨基乙醇为导向剂,用水热晶化法合成了磷酸硅锌铝分子筛纯相,测定其组成为Zn_(1.12)Si_0.38Al_(10.88)P_(11.62)O_(48),并对其结构和性能进行了研究.实验结果表明,ZnAPSO-5具有AlPO_4-5型分子筛结构,由于锌和硅进入骨架同晶取代了部分铝和磷,致使ZnAPSO-5分子筛有了B酸酸性,而热稳定性也较磷酸锌铝分子筛(ZAPO-5)有所提高.     

生物质转化中C―O/C―C键的活化断裂

Sustainable fuels and chemicals are receiving unprecedented attention worldwide in the context of achieving global carbon neutrality. Biomass, as the only natural and sustainable carbon-based source, shows great potential in addressing our current environmental/energy problems and in creating a carbon-neutral society. Lignocellulosic biomass is made up of basic structural units containing C―O/C―C bonds, and the catalytic cleavage of these C―O/C―C bonds is the key for biomass valorization; thus, garnering considerable attention in the past decade. This viewpoint begins with a brief report on the current status of catalytic activation/cleavage of C―O/C―C bonds during biomass conversion, and then goes on to discuss the key challenges experienced and possible strategies that can be implemented using cooperative catalysis. Our goal is not to provide a comprehensive overview of the activation/cleavage of the C―O/C―C bonds in biomass, but rather to highlight the core questions and challenges related to this process and the requirements for future investigations. We selected several representative C―O/C―C bonds in carbohydrates and lignin to discuss their catalytic mechanism in terms of total/selective bond cleavage, and then present our own insights for future studies. Therefore, this article mainly discusses the following two aspects: (1) The activation and cleavage of C―O bonds, which includes total and selective C―O bond cleavage in furan-based fuel precursors and lignin. When aiming to produce liquid fuels, including alkanes and arenes from biomass, the total cleavage of C―O bonds is essential. During the hydrodeoxygenation (HDO) of furan-based fuel precursors, various C―O bonds need to be cleaved, especially the C―O bond of each tetrahydrofuran ring, which has the highest bond energy. When compared with the total HDO of fuel precursors, the removal of the phenolic hydroxyl groups in lignin to produce arenes is more challenging because of the competition between the over-hydrogenation of the benzene rings and the cleavage of phenolic C―O bonds. The selective or partial cleavage of C―O/C―C bonds to form highly functionalized chemicals has recently attracted great interest and is believed to be a dynamic future research avenue. For example, the production of phenol from lignin or lignin-model compounds, through the selective removal of methoxy groups and para-side-chain groups, while preserving the phenolic hydroxyl groups, has been extensively explored in the past few years. (2) The other important aspect of this article is the cleavage of the C―C bonds in carbohydrates and lignin. The cleavage of carbohydrate C―C bonds occurs via retro-aldol condensation, which produces propylene glycol, ethylene glycol, ethanol, and lactic acid. The cleavage of C―C bonds in lignin is challenging because the bond energy of the C―C bonds is generally higher than that of the C―O bonds in lignin. Therefore, in this section, we discuss the cleavage of the strongest 5―5' bond in lignin. Finally, some subjective perspectives and future directions are provided, also highlighting several major challenges in this field.      

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。     

Ag(111)表面Ag配位结构的分等级组装

表面辅助的金属有机纳米结构因其结构稳定性和潜在应用受到广泛关注。在金属有机纳米结构中,金属原子来源于外部沉积的金属或金属表面原子。外部沉积的金属原子种类多样,取决于目标纳米结构。然而,金属表面原子受限于表面科学常用的金、银和铜单晶金属表面。金属有机纳米结构大多包括Au配位或是Cu配位结构,而只有少量的用表面Ag原子构成。分子金属相互作用的进一步研究有助于预期纳米结构的精确控制形成。至于构建基元,有机分子通过M―C、M―N和M―O键与表面金属原子配位。末端炔反应或者乌尔曼耦合能够实现C―M―C节点的形成。Cu和Au原子能够与含有末端氰基或吡啶基官能团的分子配位形成N―M―N键。另外,表面Ag增原子能够通过Ag―N配位键与酞菁分子配位。然而,M―O配位键的相关研究较少。因此,我们计划使用末端羟基分子与Ag增原子配位形成金属有机配位纳米结构去研究O―Ag节点。我们通过扫描隧道显微镜利用4, 4’-二羟基-1, 1’: 3’, 1’’-三联苯分子(4, 4’-dihydroxy-1, 1’: 3’, 1’’-terphenyl,H3PH)和Ag增原子成功构筑了一系列二维有序纳米结构。在室温下,蒸镀的H3PH分子自组装形成由环氢键连接的密堆积结构。当退火温度提升到330 K,一种新的纳米结构出现了,该结构由O―Ag配位键和氢键共同作用形成。进一步地提升退火温度至420 K,蜂巢结构和共存的二重配位链出现,这两种结构中仅由O―Ag―O键构成。为分析金属分子反应路径和O―Ag―O键的能量势垒,我们对该体系进行密度泛函理论计算。计算结果显示,O―Ag键形成的能量势垒是1.41 eV,小于O―Ag―O节点1.85 eV的能量势垒。这也解释了分等级金属-有机纳米结构形成的原因。我们的实验结果提供了一种利用有机小分子和金属增原子来设计和构筑分等级二维纳米结构的有效方法。     

纤维素及其衍生物催化脱氧转化制化学品

Biomass, as a renewable carbon resource in nature, has been considered as an ideal starting feedstock to produce various valuable chemicals, fuels, and materials, and thus, can help build a sustainable chemical industry. Because cellulose is one of the richest components in lignocellulosic biomass, the efficient transformation of cellulose plays a crucial role in biomass utilization. However, there are many oxygen-containing groups in cellulose, and therefore, the selective removal of particular functional groups from cellulose becomes an essential step in the synthesis of the chemicals or fuels that can meet the requirements set by current chemical industries. In the past decades, several efficient catalytic systems have been developed to selectively split the C―O bonds inside cellulose and its derivatives, thereby producing various valuable chemicals. In this review article, we highlight recent progress made in the selective deoxygenation of cellulose and its derived key platforms such as glucose and 5-hydroxymethyl furfural (HMF) into ethanol, dimethyl furfural (DMF), 1, 6-hexanediol (1, 6-HD), and adipic acid. The selection of these reactions is primarily because these chemicals are of great significance in chemical industries. More importantly, the formation of these chemicals represents the cleavage of different C―O bonds in biomass molecules. For instance, the synthesis of ethanol requires cleaving of only one C―O bond and two C―C bonds of the glucose unit inside cellulose. If two or more C―O bonds in the sugar or sugar acids are cleaved, olefins, oxygen-reduced sugars, and adipic acid will be attained. HMF has a furan ring linked by hydroxyl/carbonyl groups, and hence, either a furanic compound (e.g., DMF) or linear products (e.g., 1, 6-HD and adipic acid) can be synthesized by selective removal of hydroxyl/carbonyl oxygen or ring oxygen atoms. This article focuses on the selective cleavage of particular C―O bonds via heterogeneous catalysis. Efficient catalytic systems using hydrogenolysis and/or deoxydehydration strategies for these transformations are discussed. Moreover, the functions of typical catalysts and reaction mechanisms are presented to obtain insight into the C―O bond cleavage in these biomass molecules. Additionally, other factors such as reaction conditions that also influence the deoxygenation performance are analyzed. We hope that these knowledge gained on the catalytic deoxygenation of cellulose and its derived platforms will promote the rational design of effective strategies or catalysts in the future utilization of lignocellulosic biomass.     

纤维素及其衍生物催化脱氧转化制化学品

纤维素是木质纤维素生物质中最为丰富的组分,将其催化转化制备高附加值化学品在生物质资源化利用中占据极为重要的一席之地。由于纤维素中氧含量过高,需选择性地脱除部分氧原子才可获得满足当前化学工业对各类高值化学品的要求。近年来,针对纤维素以及由其衍生的关键平台分子葡萄糖和5-羟甲基糠醛(HMF)等催化脱氧的研究已引起广泛关注,并取得诸多重要进展。在此,我们总结了具有代表性的多相催化剂体系,讨论了利用氢解或脱水脱氧策略分别将纤维素和葡萄糖等分子中一个或多个C―O键裁剪制备乙醇、烯烃或己二酸等的研究。我们还着重介绍了HMF和其衍生的呋喃化合物选择性剪切C―OH/C＝O键或呋喃环中的C―O―C键分别制备二甲基呋喃和1, 6-己二醇等催化体系。此外,对各多相催化剂的作用机制和特定C―O断键机理也分别进行了探讨,以期深入理解纤维素及其衍生物的催化脱氧反应。     

普通烷烃C―H键的活化官能化

普通烷烃C―H键是指不受杂原子和碳不饱和官能团影响的sp3C―H键,如甲烷、链烷烃和环烷烃的C―H键等。它们具有较大的键能和较小的酸碱性,因而呈现惰性,通常不易在温和条件下发生断裂。同时,除个别烷烃以外,普通烷烃往往具有不同性质和不同位置的C―H键,其反应选择性也是一个难点。近半个世纪以来,金属参与的惰性C―H键活化及官能化反应得到了重视与发展。其中,在没有官能团导向作用下,过渡金属催化剂对甲烷C―H键和普通烷烃一级C―H键进行选择性亲电活化和氧化加成,从而导致官能化反应发生是比较有效的。本文介绍了这些方法的研究进展,包含机理分析以及相关反应的建立。     

Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH,IWW, and UTL by Substitution of Ge for Al

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post‐synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites ( ITH , IWW , and UTL ) on the post‐synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2–13) and IWW (Si/Ge=3–7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra‐large pore zeolite UTL (Si/Ge=4–6) the hydrolysis of the interlayer Ge?O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two‐step degermanation/alumination procedure by the partial post‐synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.     

The Structures of Uncommon Cationic N‐alkenyl Purine and Pyrimidine Bases

The structures of 1,3 bis‐(allyl)cytosinium bromide ( 1 ), 7,9 bis‐(allyl)adeninium bromide hydrate ( 2 ) and 3‐(butenyl)adeninium bromide ( 3 ) have been determined. 1 is dimeric via N―H…Br hydrogen bonds, which further associate into ribbons via weaker C―H…Br interactions. 2 is also dimeric, now from N―H…N hydrogen bonds, which build up further through a complex array of hydrogen bonds involving both the anion and water of crystallization (O―H…N, O―H…Br, C―H…Br). 3 does not dimerise but forms polymeric sheets via a series of N―H…N, C―H…N and C―H…Br hydrogen bonds.     

双金属促进的均相碳氢键活化反应

The strategy of transition-metal-catalyzed C―H activation has been greatly developed in recent years. Direct transformations of inert C―H bonds undoubtedly provide powerful ways to construct various C―C and C―X (X = heteroatom) bonds, with enhanced atom- and step-economy. Impressive efforts have been devoted to this research all along. However, concerns about reactivity and selectivity remain to be tackled, due to their strong dependence on directing groups and acidic reactive sites. In this regard, more effective catalytic systems are of great importance and therefore in high demand. Bimetallic C―H activation, by virtue of the cooperative effect, has emerged as a promising solution to this issue. The intriguing interactions between two metals with substrates afford exceptional reaction efficiency and selectivity. Intensive interest in both experimental and computational studies has been recently triggered. In this minireview, diverse bimetallic catalytic reactions are summarized into three categories according to the initiator in the C―H activation step, namely, bimetallic catalyses based on palladium, nickel, and other metals. Experimental results as well as density functional theory (DFT) calculations are invoked in the plausible mechanistic considerations. In the first part, collaborative modes based on palladium are described, in which magnesium, chromium, cobalt, and silver are successfully engaged as accessory partners. Most of them stabilize the C―H activation transition states by decreasing the energy, thus facilitating the cleavage of C―H bonds. Notably, some reactions previously reported as examples of monomeric palladium catalysis are now reinvestigated as bimetallic scenarios, in light of computational discussions. In the second part, reactions based on the synergy of nickel, and zinc or aluminum, are generalized, in which zinc or aluminum acts as a Lewis acid to increase the acidity of C―H bonds. It has been shown that the choice of different kinds of Lewis acids and ligands has a great influence on the reaction chemo-, regio-, and stereoselectivity. Gratefully, even enantioselective transformations can be achieved using the cooperation of nickel and aluminum. Moreover, a key reaction intermediate in the bimetallic C―H activation by nickel and aluminum has been isolated, providing guidance for this bimetallic catalytic system in further mechanistic studies and applications. In the last part, synergetic catalysis based on various other metals is presented. Bimetallic regimes of ruthenium/copper, rhodium/bismuth, iridium/aluminum, manganese/zinc, and zirconium/aluminum have been elegantly applied to C―H activation reactions. Multifarious action modes are proposed on account of the mechanistic research.     

Pt/NbPWO双功能催化剂的制备及氢解碱木质素制备芳香单体

Lignin is a natural aromatic polymer that accounts for nearly 30% of lignocellulose and is considered the only renewable aromatic (re)source for producing aromatic chemicals or liquid fuels via the cleavage of C―O ether bonds and C―C bonds. Thus far, the majority of investigations involving the production of valuable compounds via lignin hydrogenolysis have focused on the cleavage of relatively labile C―O bonds only, which restricts the efficiency of hydrogenolysis. Therefore, in this work, a bifunctional Pt/NbPWO catalyst was synthesized using hydrothermal and wet impregnation methods. It was found that aromatic monomers with a yield of 18.02% could be obtained by breaking the C―O and C―C bonds in alkali lignin. This reaction was applicable to breaking the key C―C bonds when the C―O ether bonds were broken in lignin polymers. The hydrogenolysis mechanism most likely involves the abundant Brønsted acid and Lewis acid sites on the catalyst that facilitate C―C bond activation. Additionally, the synergy between the support and Pt species in the Pt/NbPWO catalyst was primarily emphasized.