Current advances in precious metal core–shell catalyst design

Precious metal nanoparticles are commonly used as the main active components of various catalysts. Given their high cost, limited quantity, and easy loss of catalytic activity under severe conditions, precious metals should be used in catalysts at low volumes and be protected from damaging environments. Accordingly, reducing the amount of precious metals without compromising their catalytic performance is difficult, particularly under challenging conditions. As multifunctional materials, core–shell nanoparticles are highly important owing to their wide range of applications in chemistry, physics, biology, and environmental areas. Compared with their single-component counterparts and other composites, core–shell nanoparticles offer a new active interface and a potential synergistic effect between the core and shell, making these materials highly attractive in catalytic application. On one hand, when a precious metal is used as the shell material, the catalytic activity can be greatly improved because of the increased surface area and the closed interfacial interaction between the core and the shell. On the other hand, when a precious metal is applied as the core material, the catalytic stability can be remarkably improved because of the protection conferred by the shell material. Therefore, a reasonable design of the core–shell catalyst for target applications must be developed. We summarize the latest advances in the fabrications, properties, and applications of core–shell nanoparticles in this paper. The current research trends of these core–shell catalysts are also highlighted.     

Graphene-Encapsulated Bifunctional Catalysts with High Activity and Durability for Zn–Air Battery

Carbon-based electrocatalysts with both high activity and high stability are desirable for use in Zn–air batteries. However, the carbon corrosion reaction (CCR) is a critical obstacle in rechargeable Zn–air batteries. In this study, a cost-effective carbon-based novel material is reported with a high catalytic effect and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), prepared via a simple graphitization process. In situ growth of graphene is utilized in a 3D-metal-coordinated hydrogel by introducing a catalytic lattice of transition metal alloys. Due to the direct growth of few-layer graphene on the metal alloy decorated 3d-carbon network, greatly reduced CCR is observed in a repetitive OER test. As a result, an efficient bifunctional electrocatalytic performance is achieved with a low ΔE value of 0.63 V and good electrochemical durability for 83 h at a current density of 10 mA cm⁻² in an alkaline media. Moreover, graphene-encapsulated transition metal alloys on the nitrogen-doped carbon supporter exhibit an excellent catalytic effect and good durability in a Zn–air battery system. This study suggests a straightforward way to overcome the CCR of carbon-based materials for an electrochemical catalyst with wide application in energy conversion and energy storage devices.     

燃煤烟气中单质汞的催化氧化技术研究进展

针对燃煤电厂烟气中汞的脱除问题,综述了单质汞氧化催化剂与催化氧化机理的研究现状;着重阐述了碳基、金属及金属氧化物催化剂和选择性催化还原(SCR)催化剂对单质汞的催化氧化性能,分析了活性组分、烟气条件等对各催化剂氧化单质汞性能的影响;指出异相反应是单质汞氧化的重要途径,不同催化剂、不同烟气气氛下氧化机理不同;最后结合我国燃煤电厂的现状,提出深入研究单质汞的催化氧化机理,进一步提高SCR催化剂的催化氧化单质汞活性、抗硫性及稳定性将是燃煤烟气汞污染控制技术的重点发展方向。     

Integrated computational chemistry system for catalysts design

The understanding of valuable catalytic and adsorptive properties of heterogeneous catalysts at atomic and electronic levels is essential for the design of novel catalysts. Computer simulation studies can significantly contribute to provide a rational interpretation of the observed experimental results and suggest modification of new catalysts. Our recent work on the application of integrated computer simulation methods to investigate the structure and catalytic properties of solid surfaces including zeolites, transition metals and their oxides have been reviewed in this paper. We have emphasized the effectivity and applicability of integrated computer simulation system to solve the problems in a variety of targets of industrial and academic importance.     

ALD functionalized nanoporous gold: thermal stability, mechanical properties, and catalytic activity

Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only 1 nm thick oxide films can stabilize the nanoscale morphology of np-Au up to 1,000°C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO(2) ALD coatings. Our results open the door to high-temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.     

Electrical properties of nickel electrodes for high-k MOS structures

Together with high-κ dielectric films, metal gate electrodes have to be employed in advanced CMOS technologies. The metal gate material should be carefully selected with respect to work function, stability of metal-dielectric stack and compatibility with the CMOS process. In our investigation Ni gate electrodes grown on thermal SiO₂, atomic-layer deposition HfO₂ and Al₂O₃ dielectric films have been analyzed by means of high-frequency capacitance-voltage measurement on MOS capacitors. Ni gate materials were prepared by RF diode sputter deposition. Work function of the investigated gate material and density of effective defect charge of the gate oxide film were extracted from the measurements. These properties are discussed with regard to application of Ni metal gates in CMOS technology.     

Improving the Catalytic Activity of Carbon‐Supported Single Atom Catalysts by Polynary Metal or Heteroatom Doping

Single atom catalysts (SACs) are widely researched in various chemical transformations due to the high atomic utilization and catalytic activity. Carbon‐supported SACs are the largest class because of the many excellent properties of carbon derivatives. The single metal atoms are usually immobilized by doped N atoms and in some cases by C geometrical defects on carbon materials. To explore the catalytic mechanisms and improve the catalytic performance, many efforts have been devoted to modulating the electronic structure of metal single atomic sites. Doping with polynary metals and heteroatoms has been recently proposed to be a simple and effective strategy, derived from the modulating mechanisms of metal alloy structure for metal catalysts and from the donating/withdrawing heteroatom doping for carbon supports, respectively. Polynary metals SACs involve two types of metal with atomical dispersion. The bimetal atom pairs act as dual catalytic sites leading to higher catalytic activity and selectivity. Polynary heteroatoms generally have two types of heteroatoms in which N always couples with another heteroatom, including B, S, P, etc. In this Review, the recent progress of polynary metals and heteroatoms SACs is summarized. Finally, the barriers to tune the activity/selectivity of SACs are discussed and further perspectives presented.     

阴离子交换膜燃料电池阳极催化剂的研究进展

阴离子交换膜燃料电池(AEMFC)可使用非贵金属催化剂,且电极反应速率快。阳极催化剂的选择和制备对提高燃料氧化速率和燃料电池的电流密度及降低成本等有很大影响。本文从阴离子交换膜阳极催化剂的种类、制备方法,催化剂的载体等角度对阳极催化剂的研究现状进行分析。分析表明,在阳极催化剂中掺杂金属、金属氧化物或非金属氧化物,能充分发挥各元素的协同作用,从而提高催化剂的电催化性能;改进制备方法可以提高催化剂的比表面积,改变元素的分布。对催化剂载体进行改性以改善载体自身的孔径分布,提高比表面积和稳定性,或寻求导电性好、比表面积大、耐腐蚀的新载体材料(如SiC、Ti等),均可以提高催化剂的载量和催化剂在载体上的分散度等,从而提高阴离子交换膜燃料电池的性能。     

Metal encapsulation in zeolite particles: A rational design of zeolite-supported catalyst with maximum site activity

Zeolite-supported metal catalysts have been proven effective in many important catalytic reactions, such as hydrogenation, Fisher-Tropsch synthesis, automobile exhaust catalysis, selective catalytic reduction and many others. Despite the successful preparation of the catalyst through widely adopted methods, including ion exchange and impregnation, the metal dispersion over the zeolite is lack of control with high randomness. This renders the so-called “catalytic performance” an overall contribution from the metal sites located inside the zeolite micropores and those located on the external surface. This is exceptionally true for small to medium pore zeolites with typical free apertures of 0.3–0.6 nm (such as LTA and MFI). A more rational design of zeolite-supported metal catalysts is by encapsulating the metal nanoparticles or clusters within zeolite pores prior to the zeolite formation. Encapsulation of metals in zeolite prevents them from sintering and sulphur poisoning by cage confinement and molecular exclusion (via well-defined pore size and shape), respectively. This paper gives a new perspective on using metal clusters and nanoparticles as catalysts and the design of an effective zeolite-supported catalytic system.     

直接硼氢化物燃料电池(DBFC)阳极催化剂的研究进展

直接硼氢化物燃料电池(DBFC)具有理论电池电压高和能量密度大等特点, 而其阳极催化剂是决定电池性能的关键因素之一。因此, 研究者们在提高阳极催化剂催化活性和降低催化剂成本方面开展了大量的研究工作。本文在简要介绍DBFC工作原理和阳极反应机理的基础上, 从催化剂种类和性能角度综述了近年来DBFC中贵金属、过渡金属以及储氢合金阳极催化剂的主要研究进展, 指出了阳极催化剂研究所面临的问题, 同时提出了今后的发展方向。     

非贵金属/碳氮复合材料电催化析氧反应的研究进展

析氧反应(OER)是一种复杂的四电子转移反应,其动力学缓慢、所需能量高,制约了电解水制氢等新型能源技术的发展.近年来,非贵金属复合材料因其优异的催化活性以及相比于贵金属基催化剂的成本优势而受到广泛关注.本文概述了这一研究领域的最新进展,首先简要介绍析氧反应的机理以及材料催化性能的评价方法,重点关注非贵金属/碳氮复合材料...     

催化氧化法去除烟气中NOx的研究现状与展望

综述了SCO法(选择性催化氧化法)中催化剂的研究现状。从过渡金属元素、稀土元素、贵金属、活性炭四类催化剂进行了介绍。锰类复合氧化物催化剂具有较高的催化活性,且成本较低。钙钛矿催化剂的催化活性能与贵金属类催化剂相媲美。这些非贵金属催化剂成本都较低,具有潜在的应用价值。但总的来说目前对于催化剂抗硫抗水的研究还不够深入,一些催化剂可能还未达到实际工业应用中应具有的抗中毒能力。总结分析了SCO法应用中存在的问题,展望了其应用前景。     

Thermal Stability of Fe2O3 Nanowires

The thermal stability of α-Fe203 and γ-Fe2O3 nanowires was studied by post annealing the samples at different temperatures. Before and after annealing, the samples were characterized by X-ray diffraction and scanning electron microscopy. The α-Fe2O3 nanowires are stable at the temperatures up to 600℃, and the crystalline structure becomes more perfect after annealing. This behavior supplies a way to improve the quality of the α-Fe2O3 nanowires. The γ-Fe2O3 nanowires become unstable when annealed at 350℃. Raman spectra of both nanowires have been measured, which also indicate that the γ-Fe203 nanowires are transformed into α-Fe2O3 under the strong laser beam.     

Polypyrrole doped graphene nanocomposites as advanced positive electrodes for vanadium redox flow battery

Obtaining high catalytic activity and cycling stability of electrodes play a crucial role in vanadium redox flow batteries (VRFBs). However, some limitations, such as cost and required multiple synthesis procedures force us as an alternative solution; polypyrrole–sulfur-doped graphenes (PPy–SGs) are synthesized with a user-friendly electrochemical method and applied as a positive electrode for VRFB for the first time in the literature. Polypyrrole and sulfur-doped graphenes are formed on the graphite electrodes simultaneously in a 0.001 M pyrrole and 1.0 M H₂SO₄ solution at room temperature by a single-step cyclic voltammetry (CV) process. The electrode surface modification parameters such as the amount of S-doping, defect, and functionality rate of polymers and graphene are controlled by changing the cycle numbers at the scanned in a specific potential range. FTIR, Raman, XPS, SEM, and CV methods show the formation of PPy and sulfur-doped graphene layers on graphite electrode surfaces. The effects of PPy–SGs were investigated in VRFB for VO⁺²/VO₂⁺ redox reactions. The electrochemical measurements of the PPy–SGs are carried out by CV and electrochemical impedance spectroscopy (EIS) analysis. According to CV results, PPy–SG20 demonstrates the best performance as a positive electrode material of the VRFB. This can be attributed to the significant improvement in the electrochemical kinetics by polypyrrole decorating graphene and enhancing active sites.

     

Alloy Nanocatalysts for the Electrochemical Oxygen Reduction (ORR) and the Direct Electrochemical Carbon Dioxide Reduction Reaction (CO2RR)

In the face of the global energy challenge and progressing global climate change, renewable energy systems and components, such as fuel cells and electrolyzers, which close the energetic oxygen and carbon cycles, have become a technology development priority. The electrochemical oxygen reduction reaction (ORR) and the direct electrochemical carbon dioxide reduction reaction (CO₂RR) are important electrocatalytic processes that proceed at gas diffusion electrodes of hydrogen fuel cells and CO₂ electrolyzers, respectively. However, their low catalytic activity (voltage efficiency), limited long‐term stability, and moderate product selectivity (related to their Faradaic efficiency) have remained challenges. To address these, suitable catalysts are required. This review addresses the current state of research on Pt‐based and Cu‐based nanoalloy electrocatalysts for ORR and CO₂RR, respectively, and critically compares and contrasts key performance parameters such as activity, selectivity, and durability. In particular, Pt nanoparticles alloyed with transition metals, post‐transition metals and lanthanides, are discussed, as well as the material characterization and their performance for the ORR. Then, bimetallic Cu nanoalloy catalysts are reviewed and organized according to their main reaction product generated by the second metal. This review concludes with a perspective on nanoalloy catalysts for the ORR and the CO₂RR, and proposes future research directions.     

Porous Carbon‐Hosted Atomically Dispersed Iron–Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

As one of the alternatives to replace precious metal catalysts, transition‐metal–nitrogen–carbon (M–N–C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M–N–C catalysts can achieve good electrochemical performances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. In this work, metal–organic frameworks derived porous single‐atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further posttreatment. Combining the X‐ray absorption near‐edge spectroscopy and electrochemical measurements, the SAEs have been identified with superior oxygen reduction reaction (ORR) activity and stability compared with Pt/C catalysts in alkaline condition. More impressively, the SAEs also show excellent ORR electrocatalytic performance in both acid and neutral media. This study of nonprecious catalysts provides new insights on nanoengineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.     

Tuning Surface Structure of 3D Nanoporous Gold by Surfactant‐Free Electrochemical Potential Cycling

3D dealloyed nanoporous metals have emerged as a new class of catalysts for various chemical and electrochemical reactions. Similar to other heterogeneous catalysts, the surface atomic structure of the nanoporous metal catalysts plays a crucial role in catalytic activity and selectivity. Through surfactant‐assisted bottom‐up synthesis, the surface‐structure modification has been successfully realized in low‐dimensional particulate catalysts. However, the surface modification by top‐down dealloying has not been well explored for nanoporous metal catalysts. Here, a surfactant‐free approach to tailor the surface structure of nanoporous gold by surface relaxation via electrochemical redox cycling is reported. By controlling the scan rates, nanoporous gold with abundant {111} facets or {100} facets can be designed and fabricated with dramatically improved electrocatalysis toward the ethanol oxidation reaction.     

碳基材料掺杂聚合物导电特性研究进展

导电聚合物可分为结构型导电聚合物和复合型导电聚合物,其中复合型导电聚合物主要是碳基材料或金属掺杂聚合物而得到。文中综述了碳基材料掺杂聚合物的导电机理和碳基材料掺杂聚合物导电特性的研究进展。导电机理主要有渗滤理论、隧道效应和场致发射理论等。目前应用于复合型导电聚合物的碳基材料主要为炭黑、碳纳米管和石墨烯等。文中还简要介绍了碳基材料掺杂聚合物的应用和发展趋势。     

Metal oxide mesocrystals and mesoporous single crystals: synthesis,properties and applications in solar energy conversion

Metal oxide mesocrystals (MCs) and mesoporous single crystals (MSCs) exhibit superior carrier transport ability,high specific surface area,shortened photo-carrier diffusion lengths to interfaces and enhanced absorbance of the incident sunlight.These advanced features make metal oxide MCs and MSCs be a promising candidate material in photocatalysis,photoelectrocatalysis,dye sensitized solar cells (DSSCs) and perovskite solar cells (PSCs).Recently,remarkable advances of applying metal oxide MCs and MSCs in these areas have been achieved.Therefore,it is extremely important to deeply understand the influence of the unique properties of metal oxide MCs and MSCs on solar energy conversion systems.Herein,we presented a brief introduction on the synthesis and carrier transfer behavior of metal oxide MCs and MSCs.Then,the rational structure design and modification of metal oxide MCs and MSCs for photocatalysis,photoelectrocatalysis,DSSCs and PSCs are systematically discussed.Finally,the perspectives on extending the application of metal oxide MCs and MSCs are addressed.     

The development of gold catalysts for use in hydrogenation reactions

With increasing emphasis placed on cleaner chemical synthesis, energy efficiency and waste minimisation, the manufacture of pharmaceuticals and fine chemicals is undergoing a progressive shift from conventional stoichiometric organic processes to a harnessing of catalytic selectivity. In hydrogenation processes, gold catalysts have untapped potential in terms of selectivity in the reduction of a target functionality in multifunctional reactants. This Review provides a comprehensive evaluation of the catalytic applications of Au in hydrogenation, assessing the benefits relative to conventional transition metal (e.g. Pt, Pd and Ni) catalytic systems. Hydrogenation activity requires the formation of nanoscale Au particles that are (typically) anchored to oxide supports. The crucial catalyst structural and surface properties required to achieve enhanced hydrogenation performance in terms of rate, selectivity and stability are discussed. The synthesis procedures and characterisation methodologies directed at catalyst optimisation are evaluated. The practical application of Au catalysts is illustrated taking, as a case study, the hydrogenation of nitroaromatics, where critical features such as hydrogen adsorption/activation, structure sensitivity, metal–support interactions and active site characteristics are discussed. Commonality with the catalytic action of supported Ag is flagged with a consideration of the future outlook and direction for selective hydrogenation using Au catalysts.