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In this paper, we compare the reactivity of a series of triaryl borates B(OArx)3 as catalysts for the hydroboration of alkenes and alkynes. It was observed that commercially available B(OPh)3 performed the poorest, whereas catalysts with o-F atoms appeared to perform much better. [ABSTRACT FROM AUTHOR]

Methyltrioxorhenium(VII) (MTO) is a widely employed catalyst for metathesis, olefination, and most importantly, oxidation reactions. It is often preferred to other oxometal complexes due to its stability in air and higher efficiency. The seminal papers of K. B. Sharpless showed that when pyridine derivatives are used as co-catalysts, MTO-catalyzed olefin epoxidation with H2O2 as oxidant, a particularly useful reaction, is accelerated, with pyridine speeding up catalytic turnover and increasing the lifetime of MTO under the reaction conditions. In this paper, combined experimental and theoretical results show that the occurrence of σ-hole interactions in catalytic systems extends to MTO. Four crystalline adducts between MTO and aliphatic and heteroaromatic bases are obtained, and their X-ray analyses display short Re⋯N/O contacts opposite to both O–Re and C–Re covalent bonds with geometries consistent with σ-hole interactions. Computational analyses support the attractive nature of these close contacts and confirm that their features are typical of σ-hole interactions. The understanding of the nature of Re⋯N/O interactions may help to optimize the ligand-acceleration effect of pyridine in the epoxidation of olefins under MTO catalysis. [ABSTRACT FROM AUTHOR]

We report on the activity of fullerene-supported OsO4catalysts in the achiral dihydroxylation of olefins using N-methylmorpholine N-oxide as co-oxidant. The fullerene-supported OsO4catalysts can selectively dihydroxylate olefins with conversions up to 95% after 48 h without leaching, and the catalysts can be recovered and recycled several times. [ABSTRACT FROM AUTHOR]

The development of efficient and stable non-precious-metal-based electrocatalysts is essential for practical water splitting applications. The electrolysis of water for hydrogen production is a green and efficient method, while urea electrolysis can improve energy conversion efficiency. In this paper, W–Ni3S2/NiS catalysts with heterogeneous structures were synthesized via a one-step hydrothermal method using a W-doping-induced phase transition strategy. The doping of W modulates the morphology of the catalyst, which can form uniform nanorod arrays and improve the activity of the electrocatalyst. In an alkaline solution of 1 M KOH and 0.5 M urea, W–Ni3S2/NiS requires a potential of only 1.309 V to achieve a current density of 10 mA cm−2. An electrolyzer containing urea with W–Ni3S2/NiS as both the cathode and anode can drive a current density of 10 mA cm−2 with a potential of only 1.569 V and has relatively good stability after testing for 20 h. Experimental results show that the improvement in the catalytic activity is due to the rapid charge transfer, exposure of more active sites and better conductivity. Density functional theory calculations show that the W–Ni3S2 material exhibits higher urea adsorption energy, indicating that urea is preferentially adsorbed on its surface. The NiS material shows more state density near the Fermi level, indicating that the introduction of this material enhances the conductivity of the W–Ni3S2/NiS material. The synergistic catalysis of the two materials promoted the improvement of the catalytic activity. This work provides new ideas for the development of highly efficient and stable catalysts by means of doping and interface construction. [ABSTRACT FROM AUTHOR]

Fossil fuels have been increasingly consumed since the industrial revolution, causing rapid increases in carbon dioxide emissions and disrupting the global carbon cycle. With increasing attention being paid to the harmful effects of carbon dioxide as a "greenhouse gas", its use as a feedstock for basic chemical production is an attractive topic. Nature benefits humans through "crops brought by thunderstorms". Combining these two methods to produce urea containing nitrogen is the focus of this paper. In this paper, a series of catalysts supported on the substituted corrole substrates in the form of a double transition metal are investigated by DFT calculations. The best catalyst was selected and combined with carbon and nitrogen reduction to further explore the catalytic performance of urea synthesis. Based on this study, it was found that the synergistic catalytic strategy of double active sites had broad prospects in urea synthesis, and could also provide new development strategies for the design of other efficient molecular catalysts. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospects and electrochemical performance of hydrogen evolution catalysts, extensive research on transition metal materials has been carried out. Among the many catalytic materials, cobalt is an element with potential for the hydrogen evolution reaction (HER) due to its abundant reserves, low cost, and small energy barrier for H adsorption. This review classifies the latest research on cobalt-based catalysts according to the types of compound, including cobalt-based sulfides, phosphides, carbides, borides, oxides, etc., and summarizes the latest research progress of cobalt-based compound catalysts in acidic and alkaline media. Strategies to tune the properties of cobalt-based compound catalysts for high catalytic activity for HER are focused on, including structural engineering, defect engineering, and doping, etc. The advantages and limitations of each modified approach are reviewed. Not only that, but also the catalytic activity and advantages of the catalyst are evaluated by using density functional theory (DFT) calculation-related descriptors, activity evaluation parameters, etc. Finally, limitations and challenges of cobalt-based materials for HER are presented, as well as prospects for future research. This paper aims to understand the chemical and physical factors that affect cobalt-based catalysts, and to find directions for future research on cobalt-based catalysts. [ABSTRACT FROM AUTHOR]

Although cobalt(I) bis-phosphine complexes have been implicated in many selective C–C bond-forming reactions, until recently relatively few of these compounds have been fully characterized or have been shown to be intermediates in catalytic reactions. In this paper we present a new practical method for the synthesis and isolation of several cobalt(I)-bis-phosphine complexes and their use in Co(I)-catalyzed reactions. We find that easily prepared (in situ generated or isolated) bis-phosphine and (2,6-N-aryliminoethyl)pyridine (PDI) cobalt(II) halide complexes are readily reduced by 1,4-bis-trimethylsilyl-1,4-dihydropyrazine or commercially available lithium nitride (Li3N), leaving behind only innocuous volatile byproducts. Depending on the structures of the bis-phosphines, the cobalt(I) complex crystallizes as a phosphine-bridged species [(P∼P)(X)CoI[μ-(P∼P)]CoI(X)(P∼P)] or a halide-bridged species [(P∼P)CoI[μ-(X)]2CoI(P∼P)]. Because the side-products are innocuous, these methods can be used for the in situ generation of catalytically competent Co(I) complexes for a variety of low-valent cobalt-catalyzed reactions of even sensitive substrates. These complexes are also useful for the synthesis of rare cationic [(P∼P)CoI-η4-diene]+ X− or [(P∼P)CoI-η6-arene]+ X− complexes, which are shown to be excellent single-component catalysts for the following regioselective reactions of dienes: heterodimerizations with ethylene or methyl acrylate, hydroacylation and hydroboration. The reactivity of the single-component catalysts with the in situ generated species are also documented. [ABSTRACT FROM AUTHOR]

The synthesis of three N-heterocyclic carbene complexes by stepwise grinding is described in this paper. The benzimidazolium salts ([H2L]Br2 and [H2L](PF6)2 ([H2L] = 1,1′-di(2-picolyl)-3,3′-methylenedibenzoimidazolium)) were initially prepared. Their reactions with Ni(OAc)2·4H2O by grinding afforded three nickel complexes, [NiL]Br2·CH3OH (1), [NiL]Br2·2H2O (1′) and [NiL](PF6)2·0.5CH3CN (2), respectively. A five-coordinated complex [NiLBr]PF6 (3) was further obtained by grinding NH4PF6 with complex 1 or 1′, or grinding KBr with complex 2. Complex 3 can also be obtained by direct grinding of complexes 1/1′ and 2. Complex 3 was subsequently used as a catalyst in the C–S bond cross-coupling of 2-bromoacetophenone and 2-mercaptobenzothiazole. The entire procedure from the synthesis to the catalytic reaction was performed by mechanochemistry. The green metrics E-factor and EcoScale close to ideal values showed the eco-friendly nature of the entire procedure. [ABSTRACT FROM AUTHOR]

The treatment of mercury pollutants in water has been wide concern. Adsorption is a promising method for mercury removal that has been extensively studied. Nevertheless, the secondary application of the immobilized Hg is seldom investigated. In this paper, the Hg adsorption behavior of UiO-66 bearing sulfhydryl groups is studied. The research shows that the porous structure and sulfhydryl groups of UiO-66-SH can effectively promote the removal of mercury from water. In addition, this work also pushes forward the sequential application of the recovered adsorbent, which contains the adsorbed mercury that may cause secondary pollution. The recovered waste adsorbent, UiO-66-S-Hg, was successfully used as an efficient catalyst for transfer vinylation, which produces value-added products, vinyl benzoates. Eight vinyl esters have been successfully synthesized with a yield of up to 89%. This methodology provides a promising way for not only the treatment of mercury contamination, but also secondary pollution protection and the resource utilization of immobilized Hg. [ABSTRACT FROM AUTHOR]

It is highly desirable for porous coordination polymers (PCPs), including metal–organic frameworks (MOFs) and Prussian blue analogues (PBAs), to retain their intrinsic characteristics in electrocatalysis, instead of being used as precursors or templates for further total conversion to other compounds via high-temperature calcination. Here, a S-treated two-dimensional (2D) CoFe bimetallic PBA grown on carbon fiber paper (CFP) (named S-CoFe-PBA/CFP) is assembled and applied as a highly efficient oxygen evolution reaction (OER) electrocatalyst in 1 M KOH. The resultant S-CoFe-PBA/CFP demonstrates significantly improved OER catalytic activity; overpotentials of only 235, 259, and 272 mV are needed to drive current densities of 10, 50, and 100 mA cm−2, respectively, with a super low Tafel slope of 35.2 mV dec−1. Even more noteworthy, a current density of 90 mA cm−2 can be achieved when a potential of 1.5 V vs. RHE is applied, which is 6.4 times higher than that of commercial Ir/C in the same environment. The outstanding electrocatalytic performance can be ascribed to two reasons caused by the S-treatment process. On one hand, H+ from intermediates of *OH and *OOH can be captured by –SOx distributed on the surface of the catalyst, thus accelerating the breaking of O–H; on the other hand, partial phase transformation of CoFe-PBA leads to the in situ formation of amorphous CoSx nanogauze on the surface, and the resultant electronic interactions between the two phases contribute much to the improvement of charge transfer and adsorption for OER intermediates. This work provides a new avenue for the design of highly efficient PCP-based OER electrocatalysts. [ABSTRACT FROM AUTHOR]

Cobalt has been extensively studied as an effective catalyst for the electrooxidation of sodium borohydride. However, there is still the problem of the low catalytic activity of cobalt catalysts. The improvement in the catalytic activity of cobalt for the electrooxidation of sodium borohydride has become a challenge. In this paper, a novel catalyst Co–P alloy was supported on a copper foam (CF) substrate by a one-step electrodeposition method. In the electrodeposition process, a Co–P/CF electrode with a three-dimensional (3D) porous structure was successfully prepared using hydrogen bubbles as a dynamic template. Through the physical characterization of Co–P/CF, it was proven that the doping of P element produced more Co clusters on the surface of the electrode, which resulted in more active sites. These characteristics were very beneficial for NaBH4 electrooxidation. The electrochemical characterization confirmed that the electrocatalytic activity of Co–P/CF for NaBH4 was better than that of Co/CF. At room temperature, for the Co–P/CF in 2.0 mol dm−3 NaOH + 0.20 mol dm−3 NaBH4 solution, the oxidation current density reached 1795 mA cm−2 at −0.20 V (vs. Ag/AgCl), which was higher than that previously reported the literature. [ABSTRACT FROM AUTHOR]

A reduced graphene oxide–V2O5 nanocomposite was synthesized by a low temperature surfactant free hydrothermal method and its MFC performance was assessed. The structural properties of the synthesized nanocomposite were studied by X-ray diffraction. Field emission scanning electron microscopy of the nanocomposite revealed a wrinkled paper-like structure of rGO and a nanobelt-like structure of V2O5. This study estimated the viability of the graphene-based nanocomposite rGO–V2O5 as a novel cathode catalyst in single chamber air-cathode MFCs. A series of MFCs with different catalyst loadings were produced. The electrochemical behavior of the MFCs was calculated by cyclic voltammetry. The MFCs with the rGO–V2O5 nanocomposite cathode exhibited superior maximum power densities (83%) to those with the pure V2O5 cathodes. The rGO–V2O5 with a double-loaded nanocomposite catalyst achieved an enhanced power density of 1668 ± 11 mW m−2 and an OCP of 698 ± 4 mV, which was 83% of that estimated for the Pt/C 2004 ± 15 mW m−2 nanocomposite cathode. The significant increase in power density suggests that the reduced graphene oxide–V2O5 nanocomposite is a promising material for MFC applications. The CV result showed good agreement with the MFC result. The prepared rGO–V2O5 nanocomposite cathode, particularly with a double loading catalyst, is promising as a sustainable low-cost green material for stable power generation and long-term operation of MFCs. [ABSTRACT FROM AUTHOR]

The preceding paper (Dalton Trans., 2008, DOI: 10.1039/b806100a) describes the logical development of a chemical mechanism for the catalysis of hydrogenation of N2to 2NH3that occurs at the Fe7MoS9Nc(homocitrate) cofactor (FeMo-co) of the enzyme nitrogenase. The mechanism uses a single replenishable path for serial supply of protons which become H atoms on FeMo-co, migrating to become S–H and Fe–H donors to N2and to the intermediates that follow. This chemical catalysis at FeMo-co is distinctly intramolecular: transition states and reaction profiles for the preferred 21 step pathway were presented. This paper describes a number of alternative intermediates and pathways that were considered in developing the mechanism. These results reveal further relevant principles of the reactivity of hydrogenated FeMo-co, and the reasons why these pathways are less likely to be part of the mechanism. The intramolecular character of the mechanism, and the relatively small distances over which H atoms transfer, lead to expectations of extensive quantum mechanical hydrogen tunneling as part of the catalytic rate enhancement. This possibility is supported by comparisons of reaction profiles with those for enzyme reactions for which tunneling is established. [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NOx) and soot which come from vehicle engine exhausts cause serious environmental pollution and human health problems. Recently, the catalytic purification technology, particularly the simultaneous catalytic removal of soot and NOx, has received more and more attention. For this technology, the key is to develop highly efficient and robust catalysts. Due to the unique chemical and structural properties of layered double hydroxides (LDHs), LDH-derived catalysts have shown great potential, and much effort has been devoted to this type of catalyst. In this manuscript, we reviewed the latest progress in the LDH derived catalysts by classifying the LDH precursors according to the number of metals into binary, ternary, and quaternary, and discussed their advantages and disadvantages in detail. We hope that this review paper could provide a clearer picture of this topic and theoretical support for its better development. [ABSTRACT FROM AUTHOR]

Understanding the kinetics of olefin polymerization with Ziegler–Natta and related catalysts means identifying the main kinetic parameters such as kp and concentration of active sites. The high-pressure quenched-flow technique could be an absolute method for counting active sites and for activation studies of molecular catalysts. A kinetic study of metallocene catalysts and a phenoxy-imine titanium catalyst in the first instants of polymerization is presented in this paper. [ABSTRACT FROM AUTHOR]

This contribution reports about an in situFT-IR investigation and the catalytic reactivity of Mg/Me3+mixed oxides (Me = Cr, Fe, or Al; Mg/Me = 2, atomic ratio) in the gas-phase methylation of phenol with methanol. It is the second of two papers concerning the mentioned systems, and its purpose is twofold: to confute the classic and not accurate theory concerning the reaction mechanism, and to propose a novel interpretation based on the combined use of catalytic tests and in situmolecular spectroscopy. Results here reported highlight that: (i) the reaction mechanism in phenol methylation, when catalysed by basic systems, is not a classical electrophylic substitution, as generally reported in the literature, but proceeds through the formation of formaldehyde as an intermediate, and (ii) the catalytic behaviour in respect to both methanol and phenol reactants is strictly dependent on catalyst features. Although all investigated systems exhibit a basic-type behaviour with regard to phenol, which dissociates to yield an adsorbed phenolate species, the distribution of phenolic compounds obtained with the Mg/Al/O catalyst was that typically observed with acid catalysts, with prevailing formation of anisole when the reaction was carried out below 350 °C and of mono and poly-C-alkylated compounds when the reaction temperature was above 350 °C. On the contrary, the reactivity shown by both Mg/Fe/O and Mg/Cr/O systems was that reported in the literature as typical of mixed oxides possessing basic features. The extent of methanol decomposition into light compounds was maximum in the case of Mg/Fe/O catalysts, because of the pronounced redox behaviour typical of Fe3+species, whereas neither methanol dehydrogenation nor decomposition were ever observed with Mg/Al/O up to 400 °C. Reactivity tests and spectroscopic experiments hinted for methanol dehydrogenation to formaldehyde as the first step in the ring-methylation of phenol with Mg/Cr/O and Mg/Fe/O: in that case, o-cresol and 2,6-xylenol were the only reaction products. But, with Mg/Al/O systems, for which no methanol dehydrogenation occurred, the formation of anisole was due to the synergistic effect of stronger basic features and the presence of Lewis acidic sites, that facilitate the reaction between phenol and methanol after activation over the two different types of catalytic sites. [ABSTRACT FROM AUTHOR]

The carbonylation of methanol to acetic acid is a hugely important catalytic process, and there are considerable cost and environmental advantages if a process could be designed that was tolerant of hydrogen impurities in the CO feed gas, while eliminating by-products such as propionic acid and acetaldehyde altogether. This paper reports on an investigation into the application of rhodium complexes of several C4 bridged diphosphines, namely BINAP, 1,4-bis(diphenylphosphino)butane (dppb), bis(diphenylphosphino)xylene (dppx) and 1,4-bis(dicyclohexylphosphino)butane (dcpb) as catalysts for hydrogen tolerant methanol carbonylation. An investigation into the structure, reactivity and stability of pre-catalysts and catalyst resting states of these complexes has also been carried out in order to understand the observations in catalysis. Rh(i) carbonyl halide complexes of each of the ligands have been prepared from both [Rh2(CO)4Cl2] and dimeric μ-Cl-[Rh(L)Cl]2 complexes. These Rh(i) carbonyl complexes are either dimeric with bridging phosphine ligands (dppb, dcpb, dppx) or monomeric chelate complexes. The reaction of the complexes with methyl iodide at 140 °C has been studied, which has revealed clear differences in the stability of the corresponding Rh(iii) complexes. Surprisingly, the dimeric Rh(i) carbonyls react cleanly with MeI with rearrangement of the diphosphine to a chelate co-ordination mode to give stable Rh(iii) acetyl complexes. The Rh acetyls for L = dppb and dppx have been fully characterised by X-ray crystallography. During the catalytic studies, the more rigid dppx and BINAP ligands were found to be nearly 5 times more hydrogen tolerant than [Rh(CO)2I2]−, as revealed by by-product analysis. The origin of this hydrogen tolerance is explained based on the differing reactivities of the Rh acetyls with hydrogen gas, and by considering the structure of the complexes. [ABSTRACT FROM AUTHOR]