Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification

The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO₂-Al₂O₃ mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N₂-physisorption, powder XRD, ²⁹Si, ²⁷Al MAS-NMR, and NH₃-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to ²⁷Al and ²⁹Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH.     

钛锆复合氧化物载体的制备、物化性质及在催化反应中的应用

 TiO2-ZrO2复合氧化物具有比TiO2和ZrO2更高的比表面积、更好的热稳定性和更强的表面酸碱性,作为催化剂载体已引起很大的研究兴趣并得到了重要的应用. 本文主要介绍了TiO2-ZrO2复合氧化物载体的制备方法以及织构、结构和表面酸碱性等物化性质,并对其在催化反应中的应用进行了综述.     

A review on multi-component green synthesis of N-containing heterocycles using mixed oxides as heterogeneous catalysts

The use of mixed oxides is a well-appreciated approach in the fields of material science and synthesis, due to remarkable tunable surface properties such as acidic and basic characteristics, oxidation/reduction capabilities, and high agility of lattice oxygen, which makes them ideal choices as heterogeneous catalysts. The activity of the mixed oxides broadly relies on the nature of support and active material used and on the preparation method, calcination temperatures. Wide range of techniques for preparation of mixed oxide materials are adoptable, viz. sol-gel, co-precipitation, wet impregnation, microwave irradiation and hydrothermal methods. Use of mixed oxides as solid catalysts have gained popularity in many valued organic transformations, via alkylation, oxidation, condensation, dehydration, dehydrogenation, cycloaddition and isomerization. Application of mixed oxides in the area of green organic synthesis is a valuable strategy, which contributed significantly to the design of many novel heterocyclic scaffolds. The chemistry of N-heterocycle scaffolds, which generally possess five and six membered rings, is an interesting area for both synthetic and medicinal chemistry research constituting over 60% organics used in various arenas. The position and number of nitrogen atoms in the rings, distinguish them as pyrroles, pyrazoles, imidazoles, triazoles, pyridines and pyramidines classes. In this review, we focus on the scope, importance and versatile applications of mixed metal oxides and their synergetic effects as heterogeneous catalysts in the synthesis of variety of N-heterocyclic derivatives. The scientific aspects of the mixed oxides as catalytic active materials to design efficient synthetic protocols for the organic transformations is also discussed.     

基于石墨烯基材料的非金属液相催化反应

非金属碳基催化剂因其具有合成简单、结构稳定、比表面积大、可调控性强等特点受到了研究者的关注,已成为最活跃的研究领域之一。以二维、单原子层、六方结构的碳为基础的石墨烯和其高度氧化形态——氧化石墨烯是一类新兴的碳基材料。这类材料在催化领域的应用在近五年内才刚刚兴起。此类材料可用于烃类转化、有机化学合成、能源转化等多种催化反应,本文主要综述了采用化学氧化还原法制备的石墨烯和氧化石墨材料为催化剂的各类催化反应的最新研究进展。     

介孔Fe-Cu复合金属氧化物纳米粉催化剂催化低温CO氧化

以环氧丙烷为凝胶剂,采用简便低廉的无表面活性剂的溶胶-凝胶法制备了一系列不同Cu/Fe摩尔比的高比表面积介孔Fe-Cu复合氧化物纳米粉末。运用微反应器-色谱体系考察了它们在低温CO氧化反应中的催化性能。采用X射线衍射、N2吸附-脱附、热重-差热分析、程序升温还原、傅里叶变换红外光谱和透射电镜对所制样品进行了表征。结果表明,这些介孔Fe-Cu复合氧化物催化剂具有纳米晶结构、窄的孔径分布和高的比表面积,在低温CO氧化反应中表现出高的活性和稳定性。 CuO的添加影响了Fe2O3的结构和催化性能。当CuO含量为15 mol%时,催化剂具有最高的比表面积和催化活性,在低温CO氧化反应中表现出较高的催化稳定性。     

铈基催化剂在挥发性有机物催化燃烧治理中的研究进展

铈基催化剂由于其特殊的氧化还原性能在催化反应中得到了广泛应用,在非均相催化反应中其表面性质尤为重要.二氧化铈晶格中的氧缺陷对表面催化反应起着非常重要的作用,而二氧化铈可以有效调节催化剂表面酸碱性,修饰催化活性中心的结构,提高催化剂的储放氧能力,增强其结构稳定性和提高活性组分的分散度等.我们分别从二氧化铈催化剂的制备方法...     

阴离子层状材料的可控制备

LDHs (layered double hydroxides)是一类具有相同结构、不同物理化学性质的阴离子层状无机功能材料,作为催化剂、催化剂载体和催化剂前驱体在催化领域得到了广泛的关注. 本文综述了LDHs制备技术的最新发展,并从粒径控制、结晶度控制、形貌控制、含贵金属LDHs以及原位固载化等方面详细讨论了LDHs的可控制备技术.     

Transition-metal-free catalysts for the sustainable epoxidation of alkenes: from discovery to optimisation by means of high throughput experimentation

Transition-metal-free oxides were studied as heterogeneous catalysts for the sustainable epoxidation of alkenes with aqueous H?O? by means of high throughput experimentation (HTE) techniques. A full-factorial HTE approach was applied in the various stages of the development of the catalysts: the synthesis of the materials, their screening as heterogeneous catalysts in liquid-phase epoxidation and the optimisation of the reaction conditions. Initially, the chemical composition of transition-metal-free oxides was screened, leading to the discovery of gallium oxide as a novel, active and selective epoxidation catalyst. On the basis of these results, the research line was continued with the study of structured porous aluminosilicates, gallosilicates and silica-gallia composites. In general, the gallium-based materials showed the best catalytic performances. This family of materials represents a promising class of heterogeneous catalysts for the sustainable epoxidation of alkenes and offers a valid alternative to the transition-metal heterogeneous catalysts commonly used in epoxidation. High throughput experimentation played an important role in promoting the development of these catalytic systems.     

AlZn based Co and Ni catalysts for the partial oxidation of bioethanol — influence of different synthesis procedures

The catalytic performance of Co and Ni catalysts on AlZn mixed oxide supports depends on the synthesis procedure used for their preparation. For this study CoAlZn and NiAlZn catalysts were prepared by conventional sol-gel synthesis of the mixed oxide and subsequent impregnation of the support with the transition metal (SG = sol gel method) as well as by a single-step method were a gel is formed based on salts of all components using citric acid as chelating agent (CM = citrate method). The structure and morphology of the catalysts were characterized by nitrogen sorption, XRD and TPR measurements. They showed high activity in the partial oxidation of ethanol at 600–750 °C, but their properties depend on the preparation method. The higher performance of the catalysts prepared by the citrate method, where the transition metal is incorporated into the crystal structure of the support during preparation, is based on a change in morphology and structure, resulting in more active sites exposed on the surface. Compared to the Co catalysts, Ni catalysts showed a higher performance. This might be due to the higher reducibility and the smaller Ni particles size, which allows a better interaction with the support in NiAlZn catalysts.      

金属有机骨架HKUST-1及其衍生材料在催化中的应用进展

金属有机骨架材料(MOFs)作为异相催化剂受到了日益广泛的关注。在众多经典MOFs结构中，HKUST-1及其衍生材料是研究最多的类型之一。HKUST-1具有原料简单、易于合成、结构稳定、孔隙率高等多种优点，在异相催化领域中具有广阔的应用前景。已有多种HKUST-1相关材料被用作催化剂，包括HKUST-1本身、缺陷型结构、负载活性客体分子的复合型材料以及HKUST-1衍生的多孔碳纳米材料等。本文围绕HKUST-1作为催化剂的结构设计以及在不同催化反应中的应用展开总结与介绍，以期为相关MOFs材料的设计和催化研究提供一定参考。     

Cu-V-O氧化物催化燃烧甲苯的活性和抗硫性

采用溶胶-凝胶法制备一系列不同Cu/V比例的Cu-V-O催化剂,利用XRD、BET、H₂-TPR等手段对催化剂进行了表征,并考察其催化燃烧甲苯的活性和抗硫性。结果表明,适量的Cu掺杂会提高催化剂比表面积,而且Cu-V可以形成Cu₃V₂O₈晶型结构,使V₂O₅晶格氧活动增加,提高催化剂氧化-还原能力。其中,Cu_0.15V_0.85催化剂表现出最佳的活性和抗硫性;通过TiO₂负载可以进一步提高催化剂对甲苯的催化燃烧活性和抗硫性。     

磷酸锆及其衍生物催化剂在有机反应中的应用

简要综述了近年来磷酸锆及其衍生物催化剂的制备、组成、结构与催化性能的关系、催化机理及其在有机反应中的应用。     

在复合金属氧化物催化剂上丙烷直接氧化制丙烯酸

丙烷直接氧化制丙烯酸是近年来催化氧化的热点课题。MoVTe(Sb)NbO复合金属氧化物催化剂是该反应最重要的一类催化剂。本文对该类催化剂的制备化学包括活化方式以及决定催化性能的主要活性相结构等方面的新近认识进行了系统评述;依据丙烷催化转化的反应途径,总结了有关催化剂元素组分在反应中的作用与功能的最新进展,调变催化剂的粒子尺寸与形貌、晶相组成与结构、表面酸碱性与氧化还原性是获得优良催化性能的关键因素。     

Tailoring the catalytic performance of sol-gel-encapsulated tetra-n-propylammonium perruthenate (TPAP) in aerobic oxidation of alcohols

Sol-gel nanohybrid silica particles organically modified and doped with the ruthenium species tetra-n-propylammonium perruthenate (TPAP) are highly efficient catalysts for the selective oxidation of alcohols to carbonyl groups with O(2) at low pressure in toluene. The materials are easily prepared by a one-step sol-gel process, and their catalytic performance can be optimised by tailoring the conditions of their synthesis by hydrolytic co-polycondensation of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes R-Si(OMe)(3) in the presence of TPAP. Eventually, heterogeneous catalysts considerably more active than the unsupported perruthenate were obtained, while also being leach-proof and recyclable. The correlation between the materials' activity, surface polarity and textural properties suggests valuable information on the chemical behaviour of sol-gel catalytic materials in oxidation catalysis; this is of interest in view of the importance of efficient solid catalysts for the selective oxidation of alcohols with O(2).     

Molecular Mixed‐Metal Manganese Oxido Cubanes as Precursors to Heterogeneous Oxygen Evolution Catalysts

Well‐defined mixed‐metal [CoMn₃O₄] and [NiMn₃O₄] cubane complexes were synthesized and used as precursors for heterogeneous oxygen evolution reaction (OER) electrocatalysts. The discrete clusters were dropcasted onto glassy carbon (GC) and indium tin oxide (ITO) electrodes, and the OER activities of the resulting films were evaluated. The catalytic surfaces were analyzed by various techniques to gain insight into the structure‐function relationships of the electrocatalysts’ heterometallic composition. Depending on preparation conditions, the Co‐Mn oxide was found to change metal composition during catalysis, while the Ni–Mn oxides maintained the NiMn₃ ratio. XAS studies provided structural insights indicating that the electrocatalysts are different from the molecular precursors, but that the original NiMn₃O₄ cubane‐like geometry was maintained in the absence of thermal treatment ( 2‐Ni ). In contrast, the thermally generated 3‐Ni develops an oxide‐like extended structure. Both 2‐Ni and 3‐Ni undergo structural changes upon electrolysis, but they do not convert into the same material. The observed structural motifs in these heterogeneous electrocatalysts are reminiscent of the biological oxygen‐evolving complex in Photosystem II, including the MMn₃O₄ cubane moiety. The reported studies demonstrate the use of discrete heterometallic oxide clusters as precursors for heterogeneous water oxidation catalysts of novel composition and the distinct behavior of two sets of mixed metal oxides.     

Inorganic molecular sieves: Preparation,modification and industrial application in catalytic processes

The increasing environmental concern and promotion of “green processes” are forcing the substitution of traditional acid and base homogeneous catalysts by solid ones. Among these heterogeneous catalysts, zeolites and zeotypes can be considered as real “green” catalysts, due to their benign nature from an environmental point of view. The importance of these inorganic molecular sieves within the field of heterogeneous catalysis relies not only on their microporous structure and the related shape selectivity, but also on the flexibility of their chemical composition. Modification of the zeolite framework composition results in materials with acidic, basic or redox properties, whereas multifunctional catalysts can be obtained by introducing metals by ion exchange or impregnation procedures, that can catalyze hydrogenation–dehydrogenation reactions, and the number of commercial applications of zeolite based catalysts is continuously expanding.In this review we discuss determinant issues for the development of zeolite based catalysts, going from zeolite catalyst preparation up to their industrial application. Concerning the synthesis of microporous materials we present some of the new trends moving into larger pore structures or into organic free synthesis media procedures, thanks to the incorporation of novel organic templates or alternative framework elements, and to the use of high-throughput synthesis methods. Post-synthesis zeolite modification and final catalyst conformation for industrial use are briefly discussed.In a last section we give a thorough overview on the application of zeolites in industrial processes. Some of them are well established mature technologies, such as fluid catalytic cracking, hydrocracking or aromatics alkylation. Although the number of zeolite structures commercially used as heterogeneous catalysts in these fields is limited, the development of new catalysts is a continuous challenge due to the need for processing heavier feeds or for increasing the quality of the products. The application of zeolite based catalysts in the production of chemicals and fine chemicals is an emerging field, and will greatly depend on the discovery of new or known structures by alternative, lower cost, synthesis routes, and the fine tuning of their textural properties. Finally, biomass conversion and selective catalytic reduction for conversion of NOx are two active research fields, highlighting the interest in these potential industrial applications.     

Distinguishing homogeneous from heterogeneous catalysis in electrode-driven water oxidation with molecular iridium complexes

Molecular water-oxidation catalysts can deactivate by side reactions or decompose to secondary materials over time due to the harsh, oxidizing conditions required to drive oxygen evolution. Distinguishing electrode surface-bound heterogeneous catalysts (such as iridium oxide) from homogeneous molecular catalysts is often difficult. Using an electrochemical quartz crystal nanobalance (EQCN), we report a method for probing electrodeposition of metal oxide materials from molecular precursors. Using the previously reported [Cp*Ir(H(2)O)(3)](2+) complex, we monitor deposition of a heterogeneous water oxidation catalyst by measuring the electrode mass in real time with piezoelectric gravimetry. Conversely, we do not observe deposition for homogeneous catalysts, such as the water-soluble complex Cp*Ir(pyr-CMe(2)O)X reported in this work. Rotating ring-disk electrode electrochemistry and Clark-type electrode studies show that this complex is a catalyst for water oxidation with oxygen produced as the product. For the heterogeneous, surface-attached material generated from [Cp*Ir(H(2)O)(3)](2+), we can estimate the percentage of electroactive metal centers in the surface layer. We monitor electrode composition dynamically during catalytic turnover, providing new information on catalytic performance. Together, these data suggest that EQCN can directly probe the homogeneity of molecular water-oxidation catalysts over short times.     

Preparation of nickel-mesoporous materials and their application to the hydrodechlorination of chlorinated organic compounds

Mesoporous materials have attracted considerable attention for use as a catalyst or a catalyst support due to their remarkable textural properties such as high surface area and large pore volume with a narrow pore size distribution. Many efforts have been made to design mesoporous materials for use in heterogeneous catalyst systems. Recent progress and results regarding the preparation of nickel-mesoporous materials and their application to the hydrodechlorination of chlorinated organic compounds were discussed in this review. Mesoporous materials were used as a support for nickel catalyst or a nickel-incorporated mesoporous catalytic material in this work. Two research areas were described and discussed in this review. One is the preparation of mesoporous alumina-supported nickel catalysts and their application to the hydrodechlorination of 1,2-dichloropropane and o-dichlorobenzene. The other is the preparation of mesoporous silica-supported nickel catalysts and their application to the hydrodechlorination of 1,1,2-trichloroethane and chlorobenzene.     

Fabrication of molecularly imprinted hybrid monoliths via a room temperature ionic liquid-mediated nonhydrolytic sol-gel route for chiral separation of zolmitriptan by capillary electrochromatography

A room temperature ionic liquid (RTIL)-mediated nonhydrolytic sol-gel (NHSG) protocol was explored for the fabrication of new molecularly imprinted silica-based hybrid monoliths for chiral separation of a basic template zolmitriptan by CEC. The RTIL-mediated NHSG protocol involved free-radical copolymerization and NHSG process. Three carboxylic acids (trifluoromethyl acrylic acid, cinnamic acid, and methacrylic acid (MAA)) were examined as both the functional monomers and the catalysts for the NHSG condensation of methacryloxypropyltrimethoxysilane (MPTMS) to form silica-based framework. RTIL was incorporated to reduce gel shrinkage and also to act as the pore template. The effects of carboxylic acids and RTIL on the performance of the silica-based hybrid molecularly imprinted polymer (MIP) monoliths were investigated in detail to realize excellent chiral recognition and to give new insights into the mechanism of the RTIL-mediated NHSG strategy. Excellent chiral separation of (R)/(S)-zolmitriptan was achieved when the molar ratio of MAA to MPTMS was 1:4 and 1:2 with RTIL involved. The synergism of the free-radical copolymerization of the C=C bond of carboxylic acids and MPTMS with the NHSG condensation of MPTMS catalyzed by the carboxylic acids was demonstrated. The incorporation of RTIL increased porosity, and hence improved selectivity of the prepared hybrid monoliths.     

杂多化合物膜的制备及催化作用

Heteropoly compounds (HPC), a kind of polyoxometallates, with their strong acidity and oxidative ability, are good homogeneous and heterogeneous catalysts in both acid-catalyzed and selective oxidation reactions, and have been widely used in petroleum and fine chemical industries. Owing to the diversity in their composition and structure, the catalytic properties of HPC can be altered in a wide range. Among them, the heteropolyanions with Keggin structure have been studied by far the most,especially on their applications in heterogeneous catalysis. However, since they are thermally unstable at high temperatures, their utilization in this field has been restricted. In the last ten years, inorganic membranes have been proved to be beneficial to heterogeneous catalytic processes for their high selectivity and good heat-conductivity. And the sol-gel method, one of the most common approaches to prepare inorganic membranes, is becoming mature. Here a sol-gel method to prepare a porous HPC membrane is reported. The catalytic performance of the membrane was tested through a model reaction, the selective oxidation of t-BuOH.