Monitoring surface metal oxide catalytic active sites with Raman spectroscopy

The molecular aspect of the Raman vibrational selection rules allows for the molecular structural and reactivity determinations of metal oxide catalytic active sites in all types of oxide catalyst systems (supported metal oxides, zeolites, layered hydroxides, polyoxometalates (POMs), bulk pure metal oxides, bulk mixed oxides and mixed oxide solid solutions). The molecular structural and reactivity determinations of metal oxide catalytic active sites are greatly facilitated by the use of isotopically labeled molecules. The ability of Raman spectroscopy to (1) operate in all phases (liquid, solid, gas and their mixtures), (2) operate over a very wide temperature (-273 to >1000 °C) and pressure (UHV to ?100 atm) range, and (3) provide molecular level information about metal oxides makes Raman spectroscopy the most informative characterization technique for understanding the molecular structure and surface chemistry of the catalytic active sites present in metal oxide heterogeneous catalysts. The recent use of hyphenated Raman spectroscopy instrumentation (e.g., Raman-IR, Raman-UV-vis, Raman-EPR) and the operando Raman spectroscopy methodology (e.g., Raman-MS and Raman-GC) is allowing for the establishment of direct structure-activity/selectivity relationships that will have a significant impact on catalysis science in this decade. Consequently, this critical review will show the growth in the use of Raman spectroscopy in heterogeneous catalysis research, for metal oxides as well as metals, is poised to continue to exponentially grow in the coming years (173 references).     

酯交换法合成碳酸甲乙酯研究进展

碳酸甲乙酯(EMC)具有诸多优异的物理和化学性能,作为锂电池电解液溶剂已经被行业广泛认可,酯交换法是中国目前工业生产EMC的主要方法。本研究系统综述了碳酸酯交换反应热力学、动力学、均相及非均相催化剂、反应机理及反应工艺等方面的研究,重点评述了近五年酯交换法制备EMC的最新进展。均相催化剂中以pK_b值(碱度系数)为标准讨论了可溶碱类催化剂碱强度和催化效率之间的关系,探究了咪唑类离子液体阴、阳离子结构对反应效果的影响规律。针对工业上普遍采用的甲醇钠催化剂,描述了其失活现象并阐述了失活机理。详细比较和讨论了非均相催化剂的制备方法、表面酸碱性与催化效率之间的关系,综合评价了不同类别的催化剂催化酯交换反应的优缺点。着眼绿色、高纯、低成本EMC合成技术,高效固体碱催化剂和涉及气、液、固三相的催化精馏技术是今后开发的重点和发展方向。     

Heterogeneous Catalysis and Parahydrogen-Induced Polarization

Parahydrogen-induced polarization with heterogeneous catalysts (HET-PHIP) has been a subject of extensive research in the last decade since its first observation in 2007. While NMR signal enhancements obtained with such catalysts are currently below those achieved with transition metal complexes in homogeneous hydrogenations in solution, this relatively new field demonstrates major prospects for a broad range of advanced fundamental and practical applications, from providing catalyst-free hyperpolarized fluids for biomedical magnetic resonance imaging (MRI) to exploring mechanisms of industrially important heterogeneous catalytic processes. This review covers the evolution of the heterogeneous catalysts used for PHIP observation, from metal complexes immobilized on solid supports to bulk metals and single-atom catalysts and discusses the general visions for maximizing the obtained NMR signal enhancements using HET-PHIP. Various practical applications of HET-PHIP, both for catalytic studies and for potential production of hyperpolarized contrast agents for MRI, are described.     

Property and structure of various platinum catalysts for low-temperature carbon monoxide oxidations

The oxidation of carbon monoxide (CO) has received more attention in the last two to three decades owing to its importance in different fields. To control this CO pollution, catalytic converters have been investigated. Different types of catalysts have been used in a catalytic converter for CO emission control purposes. Platinum (Pt)-based noble metal catalysts show great potential for CO oxidation in catalytic converters with high thermal stability and tailoring flexibility. Pt metal catalysts modified with promoters such as alkali metals and reducible metal oxides have received great attention for their superior catalytic activities in CO oxidation. Temperature, close environment of the catalyst, and chemical composition in the surface layer of the catalyst have a huge effect on the active phase dispersion and O₂ adsorption capacity of the Pt metal catalysts. The main difference in activities of Pt metal catalyst for CO oxidation in O₂ or H₂ atmosphere has found. The addition of supports in Pt metal catalysts has improved their performances and reduced their cost. These improvement strongly depends on the surface structure, morphology, number of active sites, and various Pt-O interactions. Many research articles have already been published in CO oxidation over Pt metal catalysts, but no review article dedicated to CO oxidation is available in the literature.     

Non-hydrolytic sol-gel routes to heterogeneous catalysts

Oxides and mixed oxides have a tremendous importance in the field of heterogeneous catalysis, serving either as catalysts or as supports for active species. The performance of a catalyst depends directly on its composition, texture, structure and surface properties, which have to be precisely controlled and adapted to each application. In this context, the sol-gel process is a unique tool for the preparation and understanding of catalytic materials, owing to its exceptional versatility. In the last 10 years, the non-hydrolytic sol-gel (NHSG) or non-aqueous sol-gel process based on nonhydrolytic condensations in nonaqueous media has established itself as a simple and powerful method for the design of a wide range of oxide, mixed oxide and hybrid materials with controlled composition, morphology, texture and structure. NHSG proved particularly interesting for the preparation of catalytic materials, notably mesoporous xerogels, single site catalysts and highly crystalline nanoparticles. This critical review addresses the application of NHSG to the preparation of heterogeneous catalysts, emphasizing the specificities of this process, and giving a comprehensive overview of the literature (251 references).     

Synthesis and properties of poly(butylene succinate): Efficiency of different transesterification catalysts

The efficiency of organometal‐ (Ti, Zr, Sn, Hf, and Bi) and metal oxide‐ (Ge and Sb) based catalysts was investigated during the transesterification step of the synthesis of poly(butylene succinate) (PBS). PBS was prepared from succinic acid and 1,4‐butanediol via a two‐stage melt polycondensation process. The catalytic efficiency of the organometal catalysts was as follows: Ti?Zr～ Sn>Hf>Sb>Bi. The germanium and antimony metal oxides displayed desirable catalytic efficiency when were associated with hydroxy acids (lactic acid or glycolic acid), which acted as chelating agents. However, this catalytic system exhibited lower efficiency compared to the titanium system. Furthermore, at high concentrations of hydroxy acids the overall transesterification rate decreased. This effect can be explained by the substitution of PBS hydroxyl end groups by a lactic or glycolic unit, both of which are less reactive during the transesterification reaction. The role of catalytic residues during the storage and processing of PBS was also studied. The reduced viscosity of the PBS samples did not vary when processing at 190 °C from 1 to 10 minutes. However, when stored under ambient conditions, all PBS samples were prone to significant hydrolytic degradation, especially those containing a titanium catalyst. This behavior indicates that zirconium‐ and germanium‐based catalysts could be interesting substitutes for titanium‐based catalysts. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Ordered Mesoporous Silica as Supports in the Heterogeneous Asymmetric Catalysis

Enantioselective synthesis of organic compounds has been studied by homogeneous catalysts for several years. However, these catalysts have yet to make a significant impact on industrial scales for fine chemical synthesis. A primary reason is the designing of a homogeneous asymmetric catalyst, which requires relatively bulky ligands and catalyst recovery and recycling often causes problems. One of the convincing ways to overcome this problem is to immobilise the asymmetric catalyst onto a solid support and the resulting heterogeneous asymmetric catalyst system can, in principle, be readily re-used. A large number of supports such as inorganic oxides including zeolites, alumina, zirconia, silica and organic polymers have been employed as supports in heterogeneous asymmetric catalysis. Therefore, in this review article we have summarized the work done by us in our laboratory on the immobilization of chiral transition metal complexes such as Ru, Ir, Mn and Ti onto ordered mesoporous silica and its asymmetric catalysis. All these immobilized catalysts were well characterized by different physicochemical techniques to confirm the structural retention of the support as well as the active metal complex after immobilization. This report includes our asymmetric catalytic investigations in enantioselective reactions such as hydrogenation of ketones, olefins, oxidation of sulfides and oxidative kinetic resolution of alcohols and sulfoxides through immobilized heterogeneous catalyst systems.     

非均相Fenton催化剂的组成结构设计与性能优化

非均相Fenton催化技术解决了均相Fenton反应存在的问题,具有pH适用范围广以及催化剂易于回收利用等优点,因而成为水处理领域的研究热点。本文首先介绍了非均相Fenton反应用于降解有机污染物的发展、反应机理以及机理的研究方法。总结了非均相Fenton催化剂的种类,主要包括铁氧化物、其它金属氧化物、金属有机框架材料。重点讨论了提高非均相Fenton催化剂活性及稳定性的方法,包括通过调控催化剂的形貌、尺寸、孔结构使催化剂具有更高的比表面积,将活性组分负载在具有高比表面积的载体上,通过与其它金属复合以及引入光、超声、微波等外场。最后,对非均相Fenton催化技术的发展进行了展望。     

水滑石衍生的复合氧化物催化氧化挥发性有机气体的研究进展（英文）

挥发性有机化合物(VOCs)是大气颗粒污染物(PM2.5)和臭氧污染的主要前体物,来源于工业活动(如溶剂使用过程)、汽车尾气以及植物排放等,具有毒性,对人类和自然生命产生危害.催化氧化技术是在催化剂表面,在较低的操作温度(200-450℃)下,将VOCs非均相催化氧化成CO2和H2O,是一种最为有效的分解VOCs的方法,具有副产物少,能耗低的优点.VOCs分解用催化剂主要分为贵金属和金属氧化物两大类.贵金属催化剂活性高,但价格昂贵.因此科研工作者一直在诸多方面调控过渡金属氧化物,例如制备方法、组分协同、结构缺陷等,期望获得高活性、低成本的催化剂.水滑石(LDHs)是一种层状双金属氢氧化物,由带正电荷的金属氢氧化物层板和层间阴离子组成,可以表示为[M1-x^2+Mx^3+(OH)2](An-)x/n·mH2O.鉴于LDHs特有的结构特点,层板元素可调、比例可调等,其在一定温度下煅烧可以得到过渡金属复合氧化物(MMO)材料.由于LDHs的拓扑焙烧转变得到的MMO材料显示出许多利于多相催化反应的优点,如大表面积和多孔性、高热稳定性、良好的金属氧化物分散性等.水滑石基催化材料用于VOCs催化分解也引起了科研工作者的持续关注和研究,文献大多选择苯、甲苯、乙酸乙酯等工业活动中常用的挥发性有机溶剂作为探针分子来评估催化剂的活性、稳定性等参数.本综述将LDHs衍生的VOCs降解催化剂分为4类,整理了其近10年的研究进展:(1)含过渡金属的LDHs焙烧转变成MMO催化剂:系统论述了层板元素组成、层板元素比例、焙烧温度、制备方法等条件对催化活性的影响规律,阐明了不同处理条件下催化剂的物理化学特性(比表面积、孔结构、表面元素价态、氧缺陷、还原性)与催化活性的关联;(2)贵金属/MMO催化剂:比较了贵金属种类、LDHs载体种类、负载方式等因素对催化活性的影响规律,总结了贵金属负载在LDHs载体的优势;(3)核壳型MMO催化剂:分析了在氧化铝球、MOF等载体上原位负载LDHs的方法构筑多级结构的MMO催化剂,利于促进VOCs分解活性;(4)整体型MMO催化剂:满足VOCs分解实际应用,提出铝片基底上原位生长-煅烧制备高活性位点暴露的整体式催化剂的优点.在催化活性基础上着重介绍了水蒸气对活性的影响以及VOCs分解催化机理.同时提出了3点仍需努力的方向:LDHs向MMO拓扑转变机制认识不足;LDHs衍生的催化剂的VOCs分解机制研究不深入;催化剂活性降低-再生研究不透彻.     

Support Modification of Supported Nickel Catalysts for Hydrogen Production by Auto-thermal Reforming of Ethanol

Recent progress on support modification of supported nickel catalysts for hydrogen production by auto-thermal reforming of ethanol was reported in this review. Nickel catalysts supported on various materials, including metal oxides and metal oxide-stabilized mesoporous zirconias, were prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. Various experimental measurements such as NH₃-TPD (temperature-programmed desorption) and TPR (temperature-programmed reduction) were carried out to elucidate the different catalytic performance of supported nickel catalysts. It was revealed that acid property of supporting materials served as one of the important factors determining the catalytic performance. Hydrogen yield over nickel catalysts supported on metal oxides showed a volcano-shaped curve with respect to acidity of the supports. Among the catalysts tested, Ni/ZrO₂ catalyst with an intermediate acidity exhibited a superior catalytic performance. It was also observed that reducibility of nickel catalysts supported on metal oxide-stabilized mesoporous zirconias played a key role in determining the catalytic performance in the auto-thermal reforming of ethanol for hydrogen production. Hydrogen yield over nickel catalysts supported on metal oxide-stabilized zirconias increased with increasing reducibility of the catalysts (with decreasing TPR peak temperature of the catalysts).     

Developments in Titanium-Based Alkali and Alkaline Earth Metal Oxide Catalysts for Sustainable Biodiesel Production: A Review

Biodiesel represents a biodegradable, environmentally friendly, and renewable alternative to fossil fuels. Despite more than three decades of research, significant obstacles still hinder the widespread production of biodiesel. This current review elucidates both the potential and the existing challenges associated with homogeneous and heterogeneous catalysts in catalyzing biodiesel production, with a particular focus on alkali analogues, alkaline earth metal oxides, and titania-based catalysts. In particular, a comprehensive analysis is presented concerning alkali and alkaline earth-based titania (TiO₂) catalysts. Among these, the alkaline earth metal oxides, including lithium, calcium, and strontium when combined with titanium-based catalysts, exhibit superior catalytic activity compared to other metal oxides, owing to their heightened basicity. Consequently, this review offers a thorough and up-to-date insight into the potential of titania-based heterogeneous catalysts for advancing biodiesel production.     

Advanced synthesis for advancing heterogeneous catalysis

There are tremendous needs and opportunities for the understanding and application of heterogeneous catalysis in the solution of vexing technological problems. Nanoscale, catalytically active phases, particularly metal nanoparticles and metal oxide clusters, supported on high surface area oxides (supported catalysts) are one of the most important classes of heterogeneous catalysts. The problem of inhomogeneity and the limits it places on the understanding of catalytic chemistry has led to substantial efforts to produce more uniform catalyst systems via more synthetic control. This article highlights an approach adopted at Argonne National Laboratory for the synthesis of uniform supported metal and oxide particles.     

催化燃烧去除VOCs污染物的最新进展

催化燃烧是目前最有效的处理挥发性有机物(VOCs)技术之一. 本文从催化剂活性组分、催化剂载体、有效组分颗粒大小、水蒸汽的影响及催化燃烧反应中的积碳等几个方面, 对近年来催化燃烧处理VOCs的研究进行了总结. 分析表明: 贵金属催化剂的研究主要着重于选择有效的载体和双组分贵金属催化剂; 非贵金属催化剂的研究主要集中在高活性的过渡金属复合氧化物、钙钛矿和尖晶石型等催化剂的研制, 还有这些活性组分粒径大小及载体对催化燃烧VOCs反应活性的影响;此外, 在实际应用中,水蒸汽和催化剂积碳失活等问题对催化燃烧VOCs的反应也有很大影响. 本文的评述将为选择合适的催化燃烧技术处理VOCs污染物提供一定参考.     

催化燃烧去除VOCs污染物的最新进展

催化燃烧是目前最有效的处理挥发性有机物(VOCs)技术之一. 本文从催化剂活性组分、催化剂载体、有效组分颗粒大小、水蒸汽的影响及催化燃烧反应中的积碳等几个方面, 对近年来催化燃烧处理VOCs的研究进行了总结. 分析表明: 贵金属催化剂的研究主要着重于选择有效的载体和双组分贵金属催化剂; 非贵金属催化剂的研究主要集中在高活性的过渡金属复合氧化物、钙钛矿和尖晶石型等催化剂的研制, 还有这些活性组分粒径大小及载体对催化燃烧VOCs反应活性的影响;此外, 在实际应用中,水蒸汽和催化剂积碳失活等问题对催化燃烧VOCs的反应也有很大影响. 本文的评述将为选择合适的催化燃烧技术处理VOCs污染物提供一定参考.     

催化燃烧去除VOCs污染物的最新进展

催化燃烧是目前最有效的处理挥发性有机物(VOCs)技术之一. 本文从催化剂活性组分、催化剂载体、有效组分颗粒大小、水蒸汽的影响及催化燃烧反应中的积碳等几个方面, 对近年来催化燃烧处理VOCs的研究进行了总结. 分析表明: 贵金属催化剂的研究主要着重于选择有效的载体和双组分贵金属催化剂; 非贵金属催化剂的研究主要集中在高活性的过渡金属复合氧化物、钙钛矿和尖晶石型等催化剂的研制, 还有这些活性组分粒径大小及载体对催化燃烧VOCs反应活性的影响;此外, 在实际应用中,水蒸汽和催化剂积碳失活等问题对催化燃烧VOCs的反应也有很大影响. 本文的评述将为选择合适的催化燃烧技术处理VOCs污染物提供一定参考.     

催化燃烧去除VOCs污染物的最新进展

催化燃烧是目前最有效的处理挥发性有机物(VOCs)技术之一. 本文从催化剂活性组分、催化剂载体、有效组分颗粒大小、水蒸汽的影响及催化燃烧反应中的积碳等几个方面, 对近年来催化燃烧处理VOCs的研究进行了总结. 分析表明: 贵金属催化剂的研究主要着重于选择有效的载体和双组分贵金属催化剂; 非贵金属催化剂的研究主要集中在高活性的过渡金属复合氧化物、钙钛矿和尖晶石型等催化剂的研制, 还有这些活性组分粒径大小及载体对催化燃烧VOCs反应活性的影响;此外, 在实际应用中,水蒸汽和催化剂积碳失活等问题对催化燃烧VOCs的反应也有很大影响. 本文的评述将为选择合适的催化燃烧技术处理VOCs污染物提供一定参考.     

催化燃烧去除VOCs污染物的最新进展

催化燃烧是目前最有效的处理挥发性有机物(VOCs)技术之一. 本文从催化剂活性组分、催化剂载体、有效组分颗粒大小、水蒸汽的影响及催化燃烧反应中的积碳等几个方面, 对近年来催化燃烧处理VOCs的研究进行了总结. 分析表明: 贵金属催化剂的研究主要着重于选择有效的载体和双组分贵金属催化剂; 非贵金属催化剂的研究主要集中在高活性的过渡金属复合氧化物、钙钛矿和尖晶石型等催化剂的研制, 还有这些活性组分粒径大小及载体对催化燃烧VOCs反应活性的影响;此外, 在实际应用中,水蒸汽和催化剂积碳失活等问题对催化燃烧VOCs的反应也有很大影响. 本文的评述将为选择合适的催化燃烧技术处理VOCs污染物提供一定参考.     

催化燃烧去除VOCs污染物的最新进展

催化燃烧是目前最有效的处理挥发性有机物(VOCs)技术之一. 本文从催化剂活性组分、催化剂载体、有效组分颗粒大小、水蒸汽的影响及催化燃烧反应中的积碳等几个方面, 对近年来催化燃烧处理VOCs的研究进行了总结. 分析表明: 贵金属催化剂的研究主要着重于选择有效的载体和双组分贵金属催化剂; 非贵金属催化剂的研究主要集中在高活性的过渡金属复合氧化物、钙钛矿和尖晶石型等催化剂的研制, 还有这些活性组分粒径大小及载体对催化燃烧VOCs反应活性的影响;此外, 在实际应用中,水蒸汽和催化剂积碳失活等问题对催化燃烧VOCs的反应也有很大影响. 本文的评述将为选择合适的催化燃烧技术处理VOCs污染物提供一定参考.     

Recent developments of heterogeneous solid catalysts for liquid-phase Friedel–Crafts type benzylation reaction

Liquid-phase Friedel–Crafts type benzylation of aromatics has been effected traditionally with catalysis by homogeneous protonic acid or Lewis acid. However, heterogeneous catalysts have the advantages, compared to their homogeneous counterparts, of facile recovering and recycling. This short article describes the recent advances in the liquid-phase Friedel–Crafts type benzylation by benzyl chloride of aromatics over redox metal: gallium (Ga), indium (In) and thallium (Tl) containing novel heterogeneous solid catalysts. Unlike conventional acidic catalyst, the benzylation activity of the Ga-, In- or Tl-based solids does not depend solely on their acidic properties, even present; these solids in their non-acidic or basic form also shows high benzylation activity. The catalytic activity order of Ga, In and Tl containing solid catalysts supported on chemically similar inert catalyst carrier is as follows: thallium/support > indium/support > gallium/support, which is quite similar to their redox potential values indicating the role of redox function in the benzylation process. A plausible reaction mechanism for the benzylation reaction over these catalysts is proposed. These heterogeneous solids are highly efficient for the Friedel–Crafts type benzylation, even in the presence of moisture, than the conventional strongly acidic solid acid catalysts.Dedicated to Dr.Vasanth R. Choudhary, National Chemical Laboratory, Pune, India     

Uniform Heterogeneous Catalysts: The Role of Solid-State Chemistry in their Development and Design

Heterogeneous catalysts are generally assumed to be multiphasic and multicomponent; many of them are, and this is one of the resons why disentangling the factors that govern their mode of action is so difficult. But there is a large class of heterogeneous catalysts where the solid is monophasic and where the activity may be envisaged as being dispersed in a spatially uniform fashion throughout its bulk. This is true both of zeolites and many other microporous catalysts on the one hand, and of certain mixed metal oxides, where the non-stoiohiometry is inextricably mingled with the catalysis, on the other. By recognizing this broad classification numerous operational advantages follow: the performance of existing catalysts and the design of those yet to be prepared can be placed on a rational footing; moreover, the myriad techniques of solid-state chemistry and physics, often regarded as inapplicable to the subtle and special problems of surface chemistry, are seen to be of direct relevance as probes for the structure and properties of proven uniform heterogeneous catalysts as well as for the synthesis and development of new ones. This review, which draws analogies with and lessons from the chemistry of enzyme catalysts, focuses largely on the catalytic conversions of hydrocarbons over zeolites, clays, microporous AlPO₄ and a wide range of metal oxides.