核壳结构Fe3O4@UiO-66-NH2磁性纳米复合材料的合成及其催化Knoevenagel缩合反应性能

金属有机骨架(MOF)材料是由过渡金属离子与有机配体通过配位键连接构成的高度有序的超分子化合物.这类材料比表面积大,孔隙率高,热稳定性好,而且具有规整可调控的孔结构、易于功能化的骨架金属离子和有机配体,在多相催化领域具有潜在应用前景.将纳米尺寸的MOF材料等多孔材料作为催化剂,可以提高反应传质效率,从而提高催化反应活性,但纳米MOF催化剂的分离和回收困难.将磁性纳米粒子和MOF材料组装成核壳结构的磁性MOF材料,不仅可简化催化剂的分离回收,而且通过控制壳层材料的厚度可以实现催化剂的高活性和高选择性.我们曾将磁核Fe3O4纳米粒子交替放入含有一种MOF材料前体的DMF溶液中,采用层层组装法制备了磁性Fe3O4@UiO-66-NH2纳米复合材料.经过十步组装后的材料的透射电镜(TEM)结果证实为核壳结构.但未出现明显的UiO-66-NH2的X射线衍射(XRD)特征峰,说明壳层材料UiO-66-NH2的结晶度较低;同时由于其孔结构的破坏或堵塞,在反应中出现明显失活.本文进一步改进自组装方法制备了核壳结构的磁性Fe3O4@UiO-66-NH2纳米复合材料,用XRD、傅里叶变换红外光谱(FT-IR)、TEM、扫描电镜(SEM)和氮气吸附等方法对材料的组成和结构进行了表征,并考察了其在Knoevenagel缩合反应中的催化性能.结果表明,所制材料是以Fe3O4为核,以UiO-66-NH2为壳的核-壳结构材料.经三次组装后出现了一系列UiO-66-NH2的XRD特征峰,说明采用新方法制备的复合材料中壳层材料UiO-66-NH2结晶度高,晶体结构规整.N2吸附-脱附结果表明,材料具有较高的比表面积和孔容.该复合材料在Knoevenagel缩合反应中表现出与纳米UiO-66-NH2相当或更好的催化活性和选择性,而且因壳层材料的孔道限阈效应而对底物表现出尺寸选择性.由于材料结晶度和晶体结构规整度的提高,催化剂稳定性更好,通过简单磁性分离即可分离和回收催化剂,循环使用4次而未出现明显失活.相对于本课题组之前报道的Fe3O4@CuBTC-NH2,Fe3O4@IRMOF-3和Fe3O4@UiO-66-NH2材料,本文所制的Fe3O4@UiO-66-NH2是一类结构更加稳定的高效固体碱催化剂.     

核壳结构Fe_3O_4@UiO-66-NH_2磁性纳米复合材料的合成及其催化Knoevenagel缩合反应性能（英文）

金属有机骨架(MOF)材料是由过渡金属离子与有机配体通过配位键连接构成的高度有序的超分子化合物.这类材料比表面积大,孔隙率高,热稳定性好,而且具有规整可调控的孔结构、易于功能化的骨架金属离子和有机配体,在多相催化领域具有潜在应用前景.将纳米尺寸的MOF材料等多孔材料作为催化剂,可以提高反应传质效率,从而提高催化反应活性,但纳米MOF催化剂的分离和回收困难.将磁性纳米粒子和MOF材料组装成核壳结构的磁性MOF材料,不仅可简化催化剂的分离回收,而且通过控制壳层材料的厚度可以实现催化剂的高活性和高选择性.我们曾将磁核Fe_3O_4纳米粒子交替放入含有一种MOF材料前体的DMF溶液中,采用层层组装法制备了磁性Fe_3O_4@UiO-66-NH_2纳米复合材料.经过十步组装后的材料的透射电镜(TEM)结果证实为核壳结构.但未出现明显的UiO-66-NH_2的X射线衍射(XRD)特征峰,说明壳层材料UiO-66-NH_2的结晶度较低;同时由于其孔结构的破坏或堵塞,在反应中出现明显失活.本文进一步改进自组装方法制备了核壳结构的磁性Fe_3O_4@UiO-66-NH_2纳米复合材料,用XRD、傅里叶变换红外光谱(FT-IR)、TEM、扫描电镜(SEM)和氮气吸附等方法对材料的组成和结构进行了表征,并考察了其在Knoevenagel缩合反应中的催化性能.结果表明,所制材料是以Fe_3O_4为核,以UiO-66-NH_2为壳的核-壳结构材料.经三次组装后出现了一系列UiO-66-NH_2的XRD特征峰,说明采用新方法制备的复合材料中壳层材料UiO-66-NH_2结晶度高,晶体结构规整.N_2吸附-脱附结果表明,材料具有较高的比表面积和孔容.该复合材料在Knoevenagel缩合反应中表现出与纳米UiO-66-NH_2相当或更好的催化活性和选择性,而且因壳层材料的孔道限阈效应而对底物表现出尺寸选择性.由于材料结晶度和晶体结构规整度的提高,催化剂稳定性更好,通过简单磁性分离即可分离和回收催化剂,循环使用4次而未出现明显失活.相对于本课题组之前报道的Fe_3O_4@CuBTC-NH_2,Fe_3O_4@IRMOF-3和Fe_3O_4@UiO-66-NH_2材料,本文所制的Fe_3O_4@UiO-66-NH_2是一类结构更加稳定的高效固体碱催化剂.     

碳纳米管/杂多酸/聚吡咯复合催化剂的制备及催化烯烃环氧化性能

以磷钼酸(PMo)、吡咯(Py)和碳纳米管(CNTs)为原料,通过原位聚合方法制备了PPy-PMo@CNTs复合材料.采用傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等手段对材料进行了结构表征.结果表明,磷钼酸和聚吡咯被引入到碳纳米管载体上,且聚吡咯在碳纳米管表面形成了一层薄层.N2吸附-脱附测试结果表明,PPy-PMo@CNTs为介孔材料.将以乙腈为溶剂,过氧化氢为氧化剂的烯烃环氧化反应作为模型反应,考察了催化剂PPy-PMo@CNTs的催化活性.结果表明,在60℃,反应底物为1 mmol,催化剂投量为10 mg的条件下,该催化剂表现出较好的催化活性.中断和循环实验结果表明,催化剂具有较好的稳定性,在相同的反应条件下经过5次循环后,环辛烯的转化率依然保持在约65%.     

核-壳结构磁性金属有机骨架材料Fe3O4@UiO-66-NH2的合成、表征及催化性能

UiO-66-NH_2是以Zr4+为金属,以2-氨基对苯二甲酸为配体制备得到的金属有机骨架材料,它是目前报道中具有较高热稳定性和化学稳定性的材料之一。本文以Fe_3O_4为核,以UiO-66-NH_2为壳,采用层层自组装方法制备了核-壳结构的磁性金属有机骨架材料Fe_3O_4@UiO-66-NH_2。利用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)和氮气吸附等对其进行了表征,并考察了该磁性材料在克脑文盖尔(Knoevenagel)缩合反应中的催化性能。结果表明,该磁性材料Fe_3O_4@UiO-66-NH_2为核-壳结构,壳层厚度约为100 nm,氨基含量为1.70 mmol·g-1。该磁性复合材料具有Fe_3O_4和UiO-66-NH_2的双重功能,既可以磁性分离,又具有UiO-66-NH_2的孔结构和催化性能。由于壳层材料中Lewis酸性位(Zr4+)和碱性基团(-NH_2)的协同催化能力及其壳层的纳米尺寸效应,该磁性材料在Knoevenagel缩合反应中表现出和UiO-66-NH_2纳米粒子相当的催化活性。而且,通过磁性分离实现催化剂的多次循环使用后,其结构没有明显变化。     

S-型分级多孔CdS/UiO-66光催化剂的构建实现4-硝基苯胺的高效还原

金属有机框架(MOFs)材料因其高孔隙率特性在气体吸附分离、药物传递、催化等领域具有广泛应用.近年来,将功能化纳米颗粒(NPs)封装在MOFs中的研究在催化领域引起了科学家的兴趣.其中,较大比表面积的MOFs可以为NPs的分散和固定提供理想的平台,而NPs反过来可以为催化反应引入更多的活性位点,提高催化效率.然而,MOFs本身的孔隙常局限于微孔(<2 nm),这极大地限制了NPs在MOFs孔隙中的有效封装.因此,设计并制备含有介孔(2?50 nm)或大孔(>50 nm)的多级孔MOFs,揭示其孔径大小对复杂NPs/MOFs复合催化剂催化性能的影响具有重要意义.然而,具有不同孔径MOFs的可控制备具有巨大挑战性,MOFs孔径如何影响和调控NPs/MOFs复合材料催化活性是一个悬而未决的科学问题.本文结合金属离子刻蚀法和调控配体法设计了两种具有不同孔径(大孔和介孔)的UiO-66,并系统研究了孔径大小对CdS NPs的分布以及所形成的复合催化剂CdS/UiO-66的催化性能的影响及机制.我们首先阐明了UiO-66调控孔径后影响和修饰CdS NPs的空间分布:对于具有开放大孔结构的UiO-66纳米笼,CdS NPs倾向于自发沉积在UiO-66纳米笼内壁上.相比之下,CdS NPs则主要附着于介孔UiO-66的外表面.据此,具有大孔和介孔结构的CdS/UiO-66表现出不同的光催化性能.以光还原4-硝基苯胺反应为例,大孔CdS/UiO-66的反应速率常数是介孔和实心样品的3?13倍,且优于许多文献报道的CdS复合材料催化剂,表明大孔结构在制备高效复合催化材料上的潜在优势.通过光吸收能力、能级结构等计算表征,该催化剂的电子空穴对传输遵循S-型异质结光催化机制;大孔CdS/UiO-66具有较高光催化活性可归因于纳米笼对NPs的限域效应,即CdS被限制在UiO-66纳米笼内,缩短了催化剂与底物之间的电子传输距离;空心纳米笼结构则保护其内部的CdS NPs免受光腐蚀的影响,进而获得较高的催化效率和循环稳定性.可见,本文提出了一种结合离子刻蚀法和调控配体法获得具有不同孔径MOFs的有效策略,阐明了调控MOFs的孔径尺寸可以影响NPs的空间分布,是制约其性能的关键因素,有望为高效催化剂的设计及催化机制的研究提供新的依据.     

UiO-67-Sal-CuCl2在空气中催化芳香醇的选择性氧化

利用水热法一步合成了金属有机骨架(MOFs)材料UiO-67-Sal, 并将3种铜盐固定在其表面, 研究了3种铜MOFs材料催化芳香醇选择性氧化的性能. 结果表明, UiO-67-Sal-CuCl₂催化剂对芳香醇选择性氧化反应具有良好的催化活性, 且在重复使用4次后, 依然保持较好的催化效果.     

金属-有机骨架材料在烯烃氧化中的应用

本文分别从以骨架中的金属(金属簇)为催化中心的MOF材料、利用具有催化活性的刚性有机配合物构筑的MOF材料和MOF负载催化材料三个方面详细介绍了MOF作为催化剂在烯烃氧化反应中的应用情况,分析了其各自的优缺点。具有催化活性的刚性有机配合物构筑的MOF材料稳定性较好,能够引入具有光学活性的催化剂,可以作为不对称催化氧化催化剂使用,是未来的一个研究发展方向。     

气相金属催化反应综述

金属催化剂在工业、环境、能源以及生物等过程具有重要的应用.设计具有特定活性、环境友好型以及室温下具有反应活性的催化剂,需要在分子水平对金属催化剂的基元步骤,活性位点的结构以及催化反应微观机理有充分的认识.然而,由于宏观催化剂表面结构异常复杂,催化反应常受到溶剂、压力、金属颗粒团聚、催化剂表面缺陷等因素的干扰,利用现有实验仪器,从微观角度探索金属催化反应机理仍具有较大挑战,因此,对金属催化剂活性位的结构以及反应微观机理的认识还不十分清楚.质谱方法结合现代量子化学理论计算,提供了在气相条件下实验探索化学反应微观机理的有力工具,团簇反应可在隔离外界条件、可控以及可重复条件下进行,可以排除一些难以控制因素的干扰,可在化学键和分子结构水平认识金属活性位的结构以及催化反应的微观机理.气相金属团簇离子可用多种实验方法制备,与反应物分子反应后可利用多种质谱仪器探测,根据实验上所得的具有反应活性的团簇,结合现代量子化学理论模拟,得到金属催化反应的基元步骤以及微观反应机理信息,所得反应机理信息为宏观催化剂的设计提供重要理论研究基础.本综述总结了团簇实验上已经探测到的金属单原子离子、金属团簇、金属氧化物团簇和金属化合物催化的气相反应.反应物分子囊括了大量的无机和有机分子,包括CO,H2,CH4,C2H2,C2H4,C6H6,CH3OH,HCOOH,CH3COOH等.本综述主要介绍了以下三类催化反应:(1)CO催化氧化;(2)CH4催化转化;(3)催化脱羧反应,并重点关注贵金属单原子掺杂团簇独特的催化反应性.单原子催化剂可最大限度地利用有限的贵金属.在化学反应方面,单原子催化剂具有特异的反应活性,选择性以及稳定性.本综述对气相团簇反应中报道的两个重要的贵金属单原子掺杂团簇的催化反应进行了详细介绍:(1)金原子掺杂的AuAl3O3-5+团簇为首次报道的可以利用分子氧催化氧化CO的团簇单原子催化剂,我们对Au原子起催化作用的本质原因进行了介绍:(2)铂原子掺杂的PtAl3O5-7-团簇能利用分子氧催化氧化CO,该研究提出了"电负性阶梯"效应来解释Pt原子催化的微观机理,且此效应有望对大部分贵金属适用.此外,本综述对CO催化氧化反应和CH4催化转化反应的研究现状以及尚未解决的问题进行了剖析.相比CO的催化氧化反应,科学家对CH4催化转化反应机理的认识还不够深入,还需要进一步实验研究,而团簇单原子催化剂有望在此领域有所突破.     

PW11M(M=Cu、Co)@TiO2多相催化剂的制备及氧化脱硫性能

摘要：以过渡金属(Cu, Co)取代磷钨酸为模板剂,硫酸钛为钛源,通过一步模板法合成出一类多酸基PW11M(M=Cu、Co)@TiO2材料,采用FT-IR、XRD、XPS、Raman、SEM和TEM表征手段对材料进行了结构表征. 结果表明,PW11M(M=Cu、Co)被引入到TiO2中,形成了球形核壳结构. N2吸附-脱附测试表明,PW11Co@TiO2具有介孔结构:孔径大小为3.3 nm,比表面积为72.4 m2/g. 在以H2O2为氧化剂,乙腈为溶剂的氧化脱硫反应体系中考察了其催化活性,结果表明：复合材料PW11M(M=Cu、Co)@TiO2表现出良好的催化性能. 其中催化剂PW11Co@TiO2在投入量为40 mg,反应底物为500 ppm,反应温度60 oC,反应40 min后,DBT的脱硫率达到99.7%. 中断和循环实验表明,催化剂PW11Co@TiO2具有良好的稳定性,在相同的反应条件下,循环反应5次后,催化剂的催化活性没有明显下降.     

氟改性UiO-66固载钼基过氧化物催化氧化含硫化合物

采用预修饰方法对UiO-66进行配体官能团改性, 通过引入—F调控UiO-66的表面亲疏水性质; 其次, 通过引入—NH₂在UiO-66骨架上锚定MoO(O₂)₂. 接触角测试表明, 氟的引入有效地提高了载体表面的疏水性; 热重分析证明, 氟修饰的UiO-66骨架上存在更多配体缺失, 从而有效提高了整体MOF骨架的Lewis酸性. 以二苯并噻吩(DBT)氧化为氧化脱硫模型反应, 过氧化氢异丙苯(CHP)为氧化剂, 采用正交实验考察了反应温度、 氧硫比及催化剂用量对催化性能的影响, 其中氧硫比是影响DBT转化率的决定性因素. 经过氟改性后的催化剂经过5次催化反应循环后其催化活性未见明显变化, 且骨架仍保持稳定.     

Spray-Coating of Catalytically Active MOF–Polythiourea through Postsynthetic Polymerization

A UiO-66-NCS MOF was formed by postsynthetic modification of UiO-66-NH₂. The UiO-66-NCS MOFs displays a circa 20-fold increase in activity against the chemical warfare agent simulant dimethyl-4-nitrophenyl phosphate (DMNP) compared to UiO-66-NH₂, making it the most active MOF materials using a validated high-throughput screening. The −NCS functional groups provide reactive handles for postsynthetic polymerization of the MOFs into functional materials. These MOFs can be tethered to amine-terminated polypropylene polymers (Jeffamines) through a facile room-temperature synthesis with no byproducts. The MOFs are then crosslinked into a MOF–polythiourea (MOF–PTU) composite material, maintaining the catalytic properties of the MOF and the flexibility of the polymer. This MOF–PTU hybrid material was spray-coated onto Nyco textile fibers, displaying excellent adhesion to the fiber surface. The spray-coated fibers were screened for the degradation of DMNP and showed durable catalytic reactivity.     

UiO-66-NH2接枝吡啶亚胺钴系催化剂的合成及催化乙烯齐聚性能

以金属有机骨架(MOFs)UiO-66-NH2和吡啶-2-甲醛为原料,采用后合成修饰法制备一种UiO-66-NH2接枝吡啶亚胺配体,然后以UiO-66-NH2接枝吡啶亚胺配体和CoCl2·6H2O为原料,经配合反应,合成出一种UiO-66-NH2接枝吡啶亚胺钴系催化剂.采用傅里叶红外变换光谱(FT-IR)、X射线衍射(...     

多孔碳纳米纤维负载Pd纳米颗粒用于增强电催化氧还原性能

采用溶剂热法合成了以锆为金属核心、2-氨基为配体的锆基金属有机骨架（UiO-66）纳米材料,通过静电纺丝技术制备出UiO-66自由分散的聚丙烯腈（PAN/UiO-66）纤维,可控热解得到多孔碳纳米纤维（porous carbon nanofibers,PCNFs）,结合湿化学还原法在PCNFs表面沉积Pd纳米颗粒,得到PCNFs@Pd复合材料。通过扫描电子显微镜、透射电子显微镜、X射线衍射技术对其形貌、组成、结构进行表征;采用电化学工作站分别测试了PCNFs@Pd在0.1 mol·L^-1 KOH和0.1 mol·L^-1 HClO₄电解质中氧还原性能（oxygen reduction reaction,ORR）。结果表明,在PAN纤维中添加UiO-66显著提高了PCNFs@Pd（Pd负载量为0.34%）复合材料的ORR性能。相比40% Pt/C,在碱性电解质中,PCNFs@Pd复合材料展示出更低的Tafel斜率、更优异的循环稳定性和耐甲醇中毒性。在酸性电解质中也表现出类似20% Pt/C的催化活性和循环稳定性。     

Revisiting the Environment Effect on Mass Transfer for Heterogenized Pd6Ru8 Metal-Organic Cage Photocatalyst Confined within 3D Matrix

Artificial light-driven splitting of water into hydrogen involves multiple links to emulate natural photosynthesis, including light absorption, electron or energy transfer, surface catalysis et al., in which, the mass transportation of sacrificial reagent and reactant is always ignored. Metal-organic cage (MOC) of Pd₆Ru₈ (MOC-16), assembling multiple photosensitive Ru and catalytic Pd concomitant with directional electron transfer between them, provides an opportunity to explore the environmental effects from the view point of mass transportation without disturbance of other links. Zr-MOF of UiO-66 is used as a matrix to heterogenize MOC-16 and a series of characterizations are carried out to unravel the composition, structure and optical properties. The intact MOC-16 remains with long-term photo-stability and the outstanding photocatalytic activity is obtained by virtue of a long-lived triplet state. Three matrixes of ZIF-8, ZIF-8 derived carbonate CZIF, and UiO-66 are intercompared for mass transfer based on wettability and porous structure. Water molecule directly takes part in the formation of H₂ catalyzed by MOC-16@UiO-66, evidenced by a kinetic isotope effect, in addition to the proton delivery thanks to the hydrophilic nature of UiO-66. The porous structure of UiO-66 is essential for the permeation of sacrificial reagent to serve as two-electron donor, in sharp contrast as one-electron donor in nonporous CZIF matrix. These results highlight the importance of microenviroment surrounding molecular catalysts in view of the heterogenization of molecular catalysts, meanwhile, providing a prominent guidance on how to choose 3D support to bridge the homogenous and heterogenous system.     

从头算分子动力学模拟Pd团簇负载UiO-66材料结构及稳定性

采用从头算分子动力学模拟与密度泛函理论相结合的方法,计算模拟了不同尺寸的Pdn(n=1~32)金属团簇在UiO-66孔道中的稳定构型,并对金属团簇与材料骨架之间的作用方式、结合能及骨架形变能等进行了讨论.采用Bader电荷分析方法对该体系的电荷转移情况进行了计算分析.结果表明,Pdn团簇稳定负载于UiO-66材料的四面体笼中,且均呈堆积型构型.当Pd原子个数为28时体系的热力学稳定性最好,这与金属团簇和有机配体的成键方式相关,是金属团簇内部结合能和骨架形变能综合作用的结果.     

Zirconium-containing UiO-66 as an efficient and reusable catalyst for transesterification of triglyceride with methanol

Zirconium-based MOFs of the UiO family have attracted considerable attention due to their high thermal,chemical and mechanical stability. With the aim of further exploring the applications of zirconium-based UiO-66 in acid-catalyzed reactions and elucidating the effects of the defects in UiO-66 materials on their catalytic performances, in this work, a series of zirconium-containing UiO-66 samples were synthesized by varying the synthesis temperatures and BDC/Zr(terephthalic acid/ZrCl_4) ratios in the synthesis system.The synthesized UiO-66 samples were characterized by X-ray diffraction(XRD), N_2 adsorption-desorption,scanning electron microscopy(SEM), thermogravimetrical analysis(TGA), temperature-programmed desorption of NH_3(NH_3-TPD). Their catalytic performances were investigated in transesterification of tributyrin and soybean oil with methanol. The results showed that UiO-66 samples with different amounts of defects could be successfully prepared by varying the synthesis temperatures and/or the BDC/Zr ratios used in the synthesis system. The catalytic activities of the UiO-66 materials greatly depended on their linker defects and enhanced with the increase of the defect amount. The UiO-66 was an efficient catalyst for transesterification of tributyrin and soybean oil with methanol under mild reaction conditions and its catalytic activity was comparable to other solid acid catalysts reported in the literatures. The UiO-66 catalyst was relatively stable and could be reused.     

Phosphomolybdic acid supported on Schiff base functionalized graphene oxide nanosheets: Preparation,characterization, and first catalytic application in the multi‐component synthesis of tetrahydrobenzo[a]xanthene‐11‐ones

New Schiff base (SB) functionalized graphene oxide (GO) nanosheets containing phosphomolybdic counter‐anion H₂PMo₁₂O₄₀^¯ (H₂PMo) were successfully prepared by grafting of 3‐aminopropyltriethoxysilane (APTS) on GO nanosheets followed by condensation with benzil and finally reaction with phosphomolybdic acid (H₃PMo₁₂O₄₀, denoted as H₃PMo) and characterized using Fourier transform infrared (FT‐IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), particle size distribution, energy‐dispersive X‐ray (EDX) analysis, EDX elemental mapping, and inductively coupled plasma optical emission spectrometry (ICP‐OES). The prepared new nanomaterial, denoted as GO‐SB‐H₂PMo, was shown to be an efficient heterogeneous catalyst in one‐pot, three‐component reaction of β‐naphthol, aldehydes, and dimedone, giving high yields of tetrahydrobenzo[a]xanthene‐11‐ones within short reaction times. The catalyst is readily recovered by simple filtration and can be recycled and reused several times with no significant loss of catalytic activity.     

Preparation of heterogeneous cationic metalloporphyrin/heteropolyanion composite catalysts and their high catalytic activity in hydroxylation of cyclohexane with molecular oxygen

A new route to improve the metalloporphyrin catalysts is developed, and it is to constitute heterogeneous composite catalysts with immobilized cationic metalloporphyrins and heteropolyanions. By using the method of synchronously synthesizing and immobilizing porphyrins on cross-linked polystyrene microspheres (CPS microspheres), the immobilized porphyrin TAPP-CPS microspheres, on which ternary amine (TA) group-containing phenyl porphyrin (PP) was immobilized, were first prepared, and then the immobilized cationic porphyrin TMPP-CPS microspheres, in whose structure trimethylammoniophenyl porphyrin (TMPP) was contained, were obtained via quaternization reaction. Finally, three immobilized metalloporphyrins, CoTMPP-CPS (shorten as CoP-CPS), MnTMPP-CPS (MnP-CPS) and FeTMPP-CPS (FeP-CPS), were gained through coordination reactions. These immobilized metalloporphyrins were composited with heteropolyanions by right of the mutual electrostatic interaction with phosphotungstic (PW) acid and phosphomolybdic (PMo) acid as reagents, respectively, resulting in several heterogeneous metalloporphyrin/heteropolyanion composite catalysts such as CoPPW-CPS, CoPPMo-CPS and MnPPW-CPS. The composite catalysts were used in the catalytic hydroxylation reaction of cyclohexane with molecular oxygen as oxidant, and their catalytic performances were investigated. The experimental results show that the heterogeneous composite catalysts have extraordinarily high catalytic activity in the hydroxylation reaction of cyclohexane by molecular oxygen, and the cyclohexanol yield in 8 h can get up to 45.5 %. More importantly, the catalytic activity of the heterogeneous composite catalysts is obviously higher than that of the immobilized cationic metalloporphyrins, and the enhanced catalytic activity is originated from a protection of heteropolyanions against the deactivation of metalloporphyrins.     

Solid-state NMR studies of the acidity of functionalized metal–organic framework UiO-66 materials

The acid strength of metal–organic frameworks plays a key role in their catalytic performance such as activity and selectivity during catalytic reactions. Solid-state nuclear magnetic resonance in combination with probe molecules including 2-¹³C-acetone and pyridine-d₅ was employed to characterize the acid strength of UiO-66-X (X = -H, -2COOH, -SO₃H). It was found that after introduction of the functional groups, the acid strength of UiO-66-2COOH and UiO-66-SO₃H is considerably enhanced compared with that of parent UiO-66, with that of the former being similar to that of zeolite H-ZSM-5, and with that of the latter being slightly stronger than that of the former. Even though the acid density can efficiently be modified through changing the relative ratio in multivariate functionalized UiO-66-X, no significant alternation for the acid strength could be discerned in the MTV-UiO-66-X compared with acidic same-link counterpart. Theoretical calculations were employed to further confirm the acid strength of UiO-66-SO₃H and UiO-66-2COOH.