Catalytic C-H activation has emerged as a powerful tool for sustainable syntheses. In the recent years, notable success was achieved with the development of cobalt catalyzed C-H functionalizations with either in situ generated or single-component cobalt-complexes under mild reaction conditions. Herein, recent progress in the field of organometallic cobalt-catalyzed C-H activation is reviewed until November 2015.
Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technology. Though it is an eco-friendly way of producing energy for the urgent requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the hydrogen (H-2) and oxygen (O-2) fuel cell is the one with zero carbon emission and water as the only byproduct. However, supplying fuels in the purest form (at least the H-2) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H-2 production is largely dependent on steam reforming of fossil fuels, which generates CO2 along with H-2 and the source of which is going to be depleted. As an alternate, electrolysis of water has been given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H-2 produced, the abundant source, no need for high-temperature, high-pressure reactors, and so on. In earlier days, noble metals such as Pt (cathode) and Ir and Ru (anode) were used for this purpose. However, there are problems in employing these metals, as they are noble and expensive. In this review, we elaborate how the group VIII 3d metal sulfide, selenide, and phosphide nanomaterials have arisen as abundant and cheaper electrode materials (catalysts) beyond the oxides and hydroxides of the same. We also highlight the evaluation perspective of such electrocatalysts toward water electrolysis in detail.
We discuss recent developments in nanostructured molybdenum sulfide catalysts for the electrochemical hydrogen evolution reaction. To develop a framework for performing consistent and meaningful comparisons between catalysts, we review standard experimental methodologies for measuring catalyst performance and define two metrics used in this perspective for comparing catalyst activity: the turnover frequency, an intrinsic activity metric, and the total electrode activity, a device-oriented activity metric. We discuss general strategies for synthesizing catalysts with improved activity, namely, increasing the number of electrically accessible active sites or increasing the turnover frequency of each site. Then we consider a number of state-of-the-art molybdenum sulfide catalysts, including crystalline MoS2, amorphous MoSx, and molecular cluster materials, to highlight these strategies in practice. Comparing these catalysts reveals that most of the molybdenum sulfide catalysts have similar active site turnover frequencies, so the total electrode activity is primarily determined by the number of accessible active sites per geometric electrode area. Emerging strategies to overcome current catalyst limitations and potential applications for molybdenum sulfide catalysts including photoelectrochemical water splitting devices and electrolyzers are also considered.
The oxygen reduction reaction (ORR) is an important electrode reaction for energy storage and conversion devices based on oxygen electrocatalysis. This paper introduces the thermodynamics, reaction kinetics, reaction mechanisms, and reaction pathways of ORR in aqueous alkaline media. Recent advances of the catalysts for ORR were extensively reviewed, including precious metals, nonmetal-doped carbon, carbon-transition metal hybrids, transition metal oxides with spinel and perovskite structures, and so forth. The applications of those ORR catalysts to zinc-air batteries and alkaline fuel cells were briefly introduced. A concluding remark summarizes the current status of the reaction pathways, advanced catalysts, and the future challenges of the research and development of ORR
Carbon-based nanomaterials have been widely used as catalysts or catalyst supports in the chemical industry or for energy or environmental applications due to their fascinating properties. High surface areas, tunable porosity, and functionalization are considered to be crucial to enhance the catalytic performance of carbon-based materials. Recently, the newly emerging metal organic frameworks (MOFs) built from metal ions and polyfunctional organic ligands have proved to be promising self-sacrificing templates and precursors for preparing various carbon-based nanomaterials, benefiting from their high BET surface areas, abundant metal/organic species, large pore volumes, and extraordinary tunability of structures and compositions. In comparison with other carbon-based catalysts, MOF-derived carbon-based nanomaterials have great advantages in terms of tailorable morphologies and hierarchical porosity and easy functionalization with other heteroatoms and metal/metal oxides, which make them highly efficient as catalysts directly or as catalyst supports for numerous important reactions. In this perspective, we intend to give readers a survey of the research advances in the use of MOFs as self-sacrificing templates and precursors to prepare carbon-based nanomaterials, mainly including heteroatom-doped porous carbons and metal/metal oxide decorated porous carbons for applications as catalysts in energy and environment-related electrocatalysis and traditional heterogeneous catalysis. Finally, some perspectives are provided for future developments and directions of MOF-derived carbon-based materials for catalysis.
The methanol-to-olefins (MTO) reaction is an interesting and important reaction for both fundamental research and industrial application. The Dalian Institute of Chemical Physics (DICP) has developed a MTO technology that led to the successful construction and operation of the world's first coal to olefin plant in 2010. This historical perspective gives a brief summary on the key issues for the process development, including studies on the reaction mechanism, molecular sieve synthesis and crystallization mechanism, catalyst and its manufacturing scale up, reactor selection and reactor scale up, process demonstration, and commercialization. Further challenges on the fundamental research and the directions for future catalyst improvement are also suggested.
Nitrogen doping has been an effective way to tailor the properties of graphene and render its potential use for various applications. Three common bonding configurations are normally obtained when doping nitrogen into the graphene: pyridinic N, pyrrolic N, and graphitic N. This paper reviews nitrogen-doped graphene, including various synthesis methods to introduce N doping and various characterization techniques for the examination of various N bonding configurations. Potential applications of N-graphene are also reviewed on the basis of experimental and theoretical studies.
The development of high-performance nonprecious electrocatalysts with both H-2 and O-2 evolution reaction (HER and OER) activities for overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile two-step method to synthesize three-dimensional hierarchically porous urchin-like Ni2P microsphere superstructures anchored on nickel foam (Ni2P/Ni/NF) as bifunctional electrocatalysts for overall water splitting. The Ni2P/Ni/NF catalysts were prepared by template-free electro-deposition of porous nickel microspheres on nickel foam followed by phosphidation. The hierarchically macroporous E (V) superstructures with 3D configuration can reduce ion transport resistance and facilitate the diffusion of gaseous products (H-2 and O-2). The optimal Ni2P/Ni/NF exhibited remarkable catalytic performance and outstanding stability for both the HER and OER in alkaline electrolyte (1.0 M KOH). For the HER, Ni2P/Ni/NF afforded a current density of 10 mA cm(-2) at a low overpotential of only -98 mV. When it served as an OER electrocatalyst, Ni2P/Ni/NF was partially oxidized to nickel oxides/hydroxides/oxyhydroxides (mainly NiO) on the catalyst surface and exhibited excellent OER activity with small overpotentials of 200 and 268 mV to reach 10 and 100 mA cm(-2), respectively. Furthermore, when Ni2P/Ni/NF was employed as the electrocatalyst for both the cathode and anode, a water splitting electrolyzer was able to reach 10 and 100 mA cm(-2) in 1.0 M KOH at cell voltages of 1.49 and 1.68 V, respectively, together with robust durability. Various characterization techniques and controlled experiments indicated that the superior activity and strong stability of Ni2P/Ni/NF for overall water splitting originated from its electrochemically active constituents, 3D interconnected porosity, and high conductivity.
The recent explosive growth in research on catalysis by supported single metal atoms proves the scientific interest in this new frontier of heterogeneous catalysis. A supported single-atom catalyst (SAC) contains only isolated individual atoms dispersed on, and/or coordinated with, the surface atoms of an appropriate support. SACs not only maximize the atom efficiency of expensive metals but also provide an alternative strategy to tune the activity and selectivity of a catalytic reaction. When single metal atoms are strongly anchored onto high-surface-area supports, SACs offer a great potential to significantly transform the field of heterogeneous catalysis, which has been critical to enabling many important technologies. In this Perspective, I discuss the most recent advances in preparing, characterizing, and catalytically testing SACs with a focus on correlating the structural perspective of the anchored single metal atoms to the observed catalytic performances. The grand challenge to successfully developing practical SACs is to find appropriate approaches to strongly anchor the single metal atoms and to keep them stable and functional during the desired catalytic reactions. I will highlight the recent advances to overcome this barrier to develop SACs for a variety of important catalytic transformations of molecules.
To address aggravating energy and environment issues, inexpensive, highly active, and durable electrocatalysts as noble metal substitutes both at the anode and cathode are being actively pursued. Among them, heteroatom-doped graphene-based materials show extraordinary electrocatalytic performance, some even close to or outperforming the state-of-the-art noble metals, such as Pt- and IrO2-based materials. This review provides a concise appraisal on graphene doping methods, possible doping configurations and their unique electrochemical properties, including single and double doping with N, B, S, and P. In addition, heteroatom-doped graphene-based materials are reviewed as electrocatalysts for oxygen reduction, hydrogen evolution, and oxygen evolution reactions in terms of their electrocatalytic mechanisms and performance. Significantly, three-dimensional heteroatom-doped graphene structures have been discussed, and those especially can be directly utilized as catalyst electrodes without extra binders and supports.
The catalytic formation of cyclic organic carbonates (COCs) using carbon dioxide (CO2) as a renewable carbon feed stock is a highly vibrant area of research with an increasing amount of researchers focusing on this thematic investigation. These organic carbonates are highly useful building blocks and nontoxic reagents and are most commonly derived from CO2 coupling reactions with oxirane and dialcohol precursors using homogeneous catalysis methodologies. The activation of suitable reaction partners using catalysis as a key technology is a requisite for efficient CO2 conversion as its high kinetic stability poses a barrier to access functional organic molecules with added value in both academic and industrial laboratories. Although this area of science has been flourishing for at least a decade, in the past 2-3 years, significant advancements have been made to address the general reactivity and selectivity issues that are associated with the formation of COCs. Here, we present a concise overview of these activities with a primary focus to highlight the most important progress made and the opportunities that catalysis can bring about when the synthesis of these intermediates is optimized to a higher level of sophistication. The attention will be limited to those cases in which homogeneous metal-containing systems have been employed because they possess the highest potential for directed organic synthesis using CO2 as molecular building block. This review discusses examples of exceptional reactivity and selectivity, taking into account the challenging nature of the substrates that were involved, and mechanistic understanding guiding the optimization of these protocols is also highlighted.
We herein demonstrate self-doping of the CO32- anionic group into a wide bandgap semiconductor Bi2O2CO3 realized by a one-pot hydrothermal technique. The photoresponsive range of the self-doped Bi2O2CO3 can be extended from UV to visible light and the band gap can be continuously tuned. Density functional theory (DFT) calculation results demonstrate that the foreign CO32- ions are doped in the caves constructed by the four adjacent CO32- ions and the CO32- self-doping can effectively narrow the band gap of Bi2O2CO3 by lowering the conduction band position and meanwhile generating impurity level. The photocatalytic performance is evaluated by monitoring NO removal from the gas phase, photodegradation of a colorless contaminant (bisphenol A, BPA) in an aqueous solution, and photocurrent generation. In comparison with the pristine Bi2O2CO3 which is not sensitive to visible light, the self-doped Bi2O2CO3 exhibits drastically enhanced visible-light photoreactivity, which is also superior to that of many other well-known photocatalysts such as P25, C3N4, and BiOBr. The highly enhanced photocatalytic performance is attributed to combination of both efficient visible light absorption and separation of photogenerated electron hole pairs. The self-doped Bi2O2CO3 also shows decent photochemical stability, which is of especial importance for its practical applications. This work demonstrates that self-doping with an anionic group enables the band gap engineering and the design of high-performance photocatalysts sensitive to visible light.
Exploring noble-metal-free electrocatalysts with high efficiency for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) holds promise for advancing the production of H-2 fuel through water splitting. Herein, one-pot synthesis was introduced for MoS2-Ni3S2 heteronanorods supported by Ni foam (MoS2-Ni3S2 HNRs/NF), in which the Ni3S2 nanorods were hierarchically integrated with MoS2 nanosheets. The hierarchical MoS2-Ni3S2 heteronanorods allow not only the good exposure of highly active heterointerfaces but also the facilitated charge transport along Ni3S2 nanorods anchored on conducting nickel foam, accomplishing the promoted kinetics and activity for HER, OER, and overall water splitting. The optimal MoS2-Ni3S2 HNRs/NF presents low overpotentials (eta(10)) of 98 and 249 mV to reach a current density of 10 mA cm(-2) in 1.0 M KOH for HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, such heteronanorods show a quite low cell voltage of 1.50 V at 10 mA cm(-2) and remarkable stability for more than 48 h, which are among the best values of current noble-metal-free electrocatalysts. This work elucidates a rational design of heterostructures as efficient electrocatalysts, shedding some light on the development of functional materials in energy chemistry.
In this perspective, we highlight the main opportunities of metal organic frameworks (MOFs) as heterogeneous catalysts. Along with our personal view on the most promising catalytic applications, the most important issues that still need to be addressed before commercial implementation of MOF catalysis are discussed.
Spirooxindoles have become a privileged skeleton given their broad and promising activities in various therapeutic areas. The strategies and catalyst systems described here highlight recent advances in the enantioselective synthesis of spirooxindoles via organocascade strategies. Various organocatalysts with distinct activation modes have found application in constructing these sophisticated compounds. This review focuses on the enantioselective synthesis of spirooxindoles via organocascade strategies and is organized on the basis of three primary starting materials and then further subdivided according to the types of organocatalyst. These methods are of importance for the synthesis of complex natural products and the design of new pharmaceutical compounds. We believe that compounds based on spirooxindole skeletons have the potential to provide novel therapeutic agents and useful biological tools.
Hydrogen is expected to play a major role in the development of sustainable energy and environment. Electrocatalytic hydrogen evolution reaction (HER) is known as an efficient method for large-scale hydrogen production, and in this electrochemical process, efficient and low-cost electrocatalysts are indispensable. Recent advances have revealed that nanostructured molybdenum sulfides (MoSx) would be promising alternatives to Pt for the electrochemical generation of hydrogen from water. In this review, we focus on the recent progress on MoSx-based materials as electrocatalysts toward the HER under acidic condition. Moreover, future research scope and important challenges emerging from MoSx nanostructures are discussed toward the development of more advanced and efficient electrocatalysts for HER.
Electrochemical oxygen evolution and reduction reactions have received great attention due to their importance in several key technologies such as fuel cells, electrolyzers, and metal air batteries. Here, we present a simple approach to the preparation of cobalt sulfide particles in in situ grown on a nitrogen and sulfur codoped graphene oxide surface. The particle size and phase were controlled by changing the treatment temperature. Cobalt sulfide nanoparticles dispersed on graphene oxide hybrids were successfully prepared by a solid-state thermolysis approach at different temperatures (400, 500, and 600 degrees C) using cobalt thiourea and graphene oxide. X-ray diffraction studies revealed that hybrids prepared at 400 and 500 degrees C result in pure CoS2, phase, whereas the hybrid prepared at 600 degrees C exhibits Co9S8 phase. X-ray photoelectron spectroscopy studies revealed that nitrogen and sulfur simultaneously codoped on the graphene oxide surface, and these sites act to anchor the CoS2 nanoparticles strongly on the GO surface. The strong coupling between CoS2 and N,S-GO was reflected in the improvement of the oxygen electrode potential. CoS2(400)/N,S-GO showed an outstanding oxygen electrode activity with a potential of about 0.82 V against a reversible hydrogen electrode in alkaline medium, which is far better than the performance of precious catalysts such as Pt/C (1.16 V), Ru/C (1.01 V), and Ir/C (0.92 V).
Manganese is found in the active center of numerous enzymes that operate by an outer-sphere homolytic C-H cleavage. Thus, a plethora of bioinspired radical-based C-H functionalizations by manganese catalysis have been devised during the past decades. In contrast, organometallic C-H activation by means of manganese catalysis has emerged only recently as an increasingly viable tool in organic synthesis. These manganese(I)-catalyzed processes enabled a variety of C-H functionalizations with ample scope, which very recently set the stage for substitutive C- H functionalizations. The versatile manganese catalysis largely operates by an isohypsic, thus redox-neutral, mode of action through chelation assistance, and provided step-economical access to structurally divers compounds of relevance to inter alia bioorganic, agrochemical, and medicinal chemistry as well as the material sciences.
It is highly desirable but challenging to develop bifunctional catalysts for efficiently catalyzing both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy storage and conversion systems. Here a simple yet cost-effective strategy is developed to fabricate nitrogen and phosphorus dual-doped graphene/carbon nanosheets (N,P-GCNS) with N,P-doped carbon sandwiching few-layers-thick graphene. The as-prepared N,P-GCNS shows outstanding catalytic activity toward both ORR and OER with a potential gap of 0.71 V between the OER potential at a current density of 10 mA cm(-2) and the ORR potential at a current density of -3 mA cm(-2), illustrating that it is the best metal-free bifunctional electrocatalysts reported to date. The superb bifunctional catalytic performance is attributed to the synergistic effects between the doped N and P atoms, the full exposure of the active sites on the surface of the N,P-GCNS nanosheets, the high conductivity of the incorporated graphene, and the large surface area and hierarchical pores for sufficient contact and rapid transportation of the reactants.