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This work describes a highly active and stable acid activated carbon fibre and amorphous MoSx composite hydrogen evolution catalyst. The increased electrochemical-surface area is demonstrated to cause increased catalyst electrodeposition and activity. These composite electrodes also show an improved stability towards the mechanical degradation of the MoSx catalyst. [ABSTRACT FROM AUTHOR]

This work describes a new well-defined, air-stable, phosphine free palladium(II) [Pd(L)Cl] (1) catalyst. This catalyst was utilized for N-alkylation of amines and indole synthesis where H2O was found to be the by-product. A broad range of aromatic amines were alkylated using this homogeneous catalyst with a catalyst loading of 0.1 mol%. Greener aromatic and aliphatic primary alcohols were utilized and a hydrogen auto-transfer strategy via a metal–ligand cooperative approach was investigated. The precursor of the antihistamine-containing drug molecule tripelennamine was synthesized on a gram scale for large-scale applicability of the current synthetic methodology. A number of control experiments were performed to investigate the possible reaction pathway and the outcomes of these experiments indicated the azo-chromophore as a hydrogen reservoir during the catalytic cycle. [ABSTRACT FROM AUTHOR]

A new method for the generation of benzyl radicals from terminal aromatic alkynes has been developed, which allows the direct cross coupling with acrylate derivatives. Our additive-free protocol employs air-stable diamino Mo3S4 cubane-type cluster catalysts in the presence of hydrogen. A sulfur-centered cluster catalysis mechanism for benzyl radical formation is proposed based on catalytic and stoichiometric experiments. The process starts with the cluster hydrogen activation to form a bis(hydrosulfido) [Mo3(μ3-S)(μ-S)(μ-SH)2Cl3(dmen)3]+ intermediate. The reaction of various aromatic terminal alkynes containing different functionalities with a series of acrylates affords the corresponding Giese-type radical addition products. [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]

One-pot three-component synthesis of α-methylated ketones from secondary and primary alcohols via a triple dehydrogenative method is presented here. This protocol uses a polystyrene-supported catalyst and the catalyst is reused for five runs without any drop in its activity. Detailed mechanistic investigation was carried out with control reactions and deuterium labelling experiments revealed that secondary and primary alcohols act as a hydrogen source in this one-pot synthesis of α-methylated substituted ketones. [ABSTRACT FROM AUTHOR]

In this work, an innovative route for upgrading biomass-derived phenolic monomers by "hydrogen-free" hydrodeoxygenation (HDO) was proposed and evaluated. The HDO process was integrated with the activation of water and aqueous phase reforming of in situ generated methanol over a nano-porous Ni catalyst and finally the one-pot approach was established achieving high selectivity of bio-phenol. DFT calculations confirmed the crucial role of the Ni catalyst in the activation of water and the following HDO process. The study of the reaction pathway and the mechanism showed that the initial hydrogen source came from water splitting on the surface of the Ni catalyst, which triggered the fracture of the aromatic ether bond to afford phenol and methanol. The subsequent aqueous phase reforming of methanol generated more hydrogen and further accelerated the HDO process. Under the optimized conditions the conversion of guaiacol reached 41.5% and the selectivity of phenol can be 100% at 160 °C. On further increasing the temperature to 190 °C, a high conversion of 96.3% could be achieved while maintaining the selectivity of phenol to 77.9%. After a smart design of methanol release during the reaction, the conversion and selectivity could be further improved to 90.5% and 90.3%, respectively. Overall, the proposed method demonstrates the feasibility of upgrading oxygen-containing biological compounds in a neat water system integrating chemo-splitting of water with using endogenous hydrogen for self-hydrolysis inhibiting external hydrogen supply. [ABSTRACT FROM AUTHOR]

The importance of photocatalytic hydrogen evolution is increasing in energy research and environmental catalysis. Co-MOF, a metal–organic framework compound with a zeolite topological structure, has the advantage of being a semiconductor in photocatalytic applications. The new composite materials constructed by coupling Co-MOF with traditional semiconductors will significantly stimulate the potential of photocatalysis due to the construction of a heterogeneous interface. We accurately controlled the growth of Co-MOF with different morphologies by adjusting the ratio of raw materials. With the increase of dimethylimidazole, hexagonal prism morphology (Co-MOF-H), leaf morphology (Co-MOF-B), and Daisy morphology (Co-MOF-D) were successively synthesized. The experimental results show that H-g-C3N4 has the best catalytic activity when adsorbing hexagonal prism Co-MOF. When the ratio of H-g-C3N4 reached 125 mg, the optimal hydrogen evolution activity reached 1033 μmol g−1 h−1. Various characterization methods were used to explain the influence of morphology regulation on the hydrogen evolution ability of Co-MOF and explore the mechanism of hydrogen evolution of Co-MOF/H-g-C3N4 composite catalysts. [ABSTRACT FROM AUTHOR]

As a narrow bandgap semiconductor, transition metal selenides are promising as excellent electrocatalysts for hydrogen evolution reactions (HERs). Herein, using an ultra-thin MOF as the precursor, a Co-doped core–shell shaped NiSe2 based catalyst is successfully constructed by a two-step calcination method as an efficient HER catalyst. Experiments and theoretical calculations indicate that the introduction of Co adjusts the electronic structure of Ni and Se, promoting charge transfer and reducing the energy barrier of the rate-limiting step to accelerate the hydrogen precipitation reaction. In addition, the core–shell structure contributes to mass transport, and the outer carbon layer improves the stability of the catalyst. The optimal catalyst (Ni0.75Co0.25Se2@NC) exhibited satisfactory electrocatalytic activity as evidenced by a low overpotential of −143 mV at a current density of −10 mA cm−2 and a small Tafel slope of 37.5 mV dec−1. This work provides a valuable strategy for fabricating efficient NiSe2 based electrocatalysts for the HER. [ABSTRACT FROM AUTHOR]

An effective and safe route is proposed to prepare supported Mo2C-based catalysts from organic–inorganic hybrids, which exhibit high activity and stability for producing H2from methanol catalytic decomposition. [ABSTRACT FROM AUTHOR]

The development of efficient and low-cost catalysts is of great significance for the future application of the electrocatalytic hydrogen evolution reaction (HER). Herein, a series of Ni,N co-doped Mo2C nanostructures (Nix–Mo2C/N) with different Ni content levels are fabricated. The phase-directing effect of Ni on Mo2C/N is observed, which is in charge of the phase transformation of Mo2C/N from an α- to a β-phase. At the optimized Ni-doping level, biphase Ni15–Mo2C/N exhibits outstanding HER activity under both acidic and alkaline conditions. In particular, under alkaline conditions, Ni15–Mo2C/N delivers an overpotential of only 105.0 mV, accompanied by a low Tafel slope of 44.96 mV dec−1. The performance is comparable to commercial 20% Pt/C and higher than most state-of-the-art Mo2C-based catalysts as well. [ABSTRACT FROM AUTHOR]

Recently, much attention has been focused on the development of photocatalysts for hydrogen evolution. Up to now, efficient hydrogen generation is still greatly challenging due to the restraints of the surface redox reaction rate, and the introduction of a co-catalyst is one of the keys to this problem. Here, dual non-noble co-catalysts NixP and Mn3O4 were proposed and prepared on a g-C3N4/red phosphorus (CNP) hybrid structure with a high light adsorption capability by a two-step photo-deposition method. The photo-excited charge on the composite catalyst separate and transfer from C3N4 to red phosphorous due to a type I heterojunction structure. NixP and Mn3O4 act as reductive and oxidative co-catalysts, respectively. The hydrogen production rate was 5851.3 μmol g−1 h−1, 12.4 times that of pure CNP. The consistent catalytic activity in an actual 25 mL flask for hydrogen evolution over eight hours accumulated 245.08 μmol H2 under solar simulated irradiation. This work provides practical reference for the development of a novel inexpensive photocatalyst system. [ABSTRACT FROM AUTHOR]

Currently, two-dimensional (2D) layered transition metal chalcogenides (TMCs), especially MoS2, are attracting widespread attention in the field of water electrolysis. Unfortunately, the catalytic activity of MoS2 is limited to a few edge sites and by its low conductivity. Herein, MoS2/NiS heterostructures possessing a flower-like morphology were constructed via an accurate thermal treatment process to realize precise interface modification. As expected, through the adjunction of a certain amount of polyvinylpyrrolidone, NiS grew uniformly on the surface of MoS2 nanosheets, thereby forming a large number of visual lattice fringes with a specific interplanar spacing, which promoted a higher electron-transfer efficiency. The better electron-transfer efficiency resulted in a better hydrogen evolution reaction performance, providing an overpotential of 158 mV at 10 mA cm−1, a Tafel slope of 128.1 mV dec−1, and significantly long-term durability. Moreover, density functional theory calculation also showed that the precise interface modification of MoS2/NiS heterostructure exhibited more occupations at the Fermi level, which improved the electrical conductivity. Additionally, the MoS2/NiS catalysts achieved a moderately lower hydrogen adsorption energy (ΔGH*), indicating that it had better catalytic hydrogen evolution performance. This work can be extended to design other catalytic materials and for understanding reactions in the fields of energy conversion through theoretical calculations. [ABSTRACT FROM AUTHOR]

A synergistic combination of photoredox and polarity reversal catalysis enabled a hydrogen evolution cross-coupling of silanes with H2O, alcohols, phenols, and silanols, which afforded the corresponding silanols, monosilyl ethers, and disilyl ethers, respectively, in moderate to excellent yields. The dehydrogenative cross-coupling of Si–H and O–H proceeded smoothly with broad substrate scope and good functional group compatibility in the presence of only an organophotocatalyst 4-CzIPN and a thiol HAT catalyst, without the requirement of any metals, external oxidants and proton reductants, which is distinct from the previously reported photocatalytic hydrogen evolution cross-coupling reactions where a proton reduction cocatalyst such as a cobalt complex is generally required. Mechanistically, a silyl cation intermediate is generated to facilitate the cross-coupling reaction, which therefore represents an unprecedented approach for the generation of silyl cation via visible-light photoredox catalysis. [ABSTRACT FROM AUTHOR]

Photocatalytic water splitting is a promising approach to convert solar energy into storable hydrogen fuel. In theory, the optimization of light-harvesting and catalytic molecular conversion ability is necessary for high-efficiency hydrogen evolution; however, the establishment of a photocatalytic system composed of a light-harvesting center and an active center is limited by poor light absorption capacity, high overpotential for catalytic conversion, as well as the low efficiency of charge transfer between the two components. In this work, we demonstrate that a high-efficiency photocatalytic system consisting of two-dimensional carbon nitride (2D-C3N4) as the light-harvester and nickel sulfide (NiSx) as the active component can serve as an efficient catalyst for hydrogen evolution, wherein the tight interface formed using two-step solvothermal treatment bridges the charge transfer. The 2D structure of 2D-C3N4 can shorten the charge migration distance from the bulk to the contact interface with NiSx and minimize the charge recombination in the light-harvesting center. NiSx with a highly active surface can capture the photo-generated electrons through a tight contact interface, completing the conversion from H+ to H2. As a result, the hydrogen evolution rate of the optimal NiSx/2D-C3N4 catalyst achieves a high value of ∼4640 μmol g−1 h−1 under visible light irradiation, which is more active than most of the Pt-free 2D-C3N4 supported photocatalysts under the same reaction conditions. [ABSTRACT FROM AUTHOR]

The present study deals with the material tailoring of Mg(NH2)2–2LiH through dual borohydrides: the reactive LiBH4 and the non-reactive NaBH4. Furthermore, a pulverizer, as well as a catalyst FeTi, has been added in order to facilitate hydrogen sorption. Addition of LiBH4 to LiNH2 in a 1 : 3 molar ratio leads to the formation of Li4(BH4)(NH2)3 which also acts as a catalyst. However, the addition of NaBH4 doesn't lead to any compound formation but shows a catalytic effect. The onset dehydrogenation temperature of thermally treated Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4) is 142 °C as against 196 °C for the basic material Mg(NH2)2–2LiH. However, with the FeTi catalyzed Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4, it has been reduced to 120 °C. This is better than other similar amide/hydride composites where it is 149 °C (when the basic material is catalyzed with LiBH4). The FeTi catalyzed Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4 sample shows better de/re-hydrogenation kinetics as it desorbs 3.9 ± 0.04 wt% and absorbs nearly 4.1 ± 0.04 wt% both within 30 min at 170 °C (with the H2 pressure being 0.1 MPa for desorption and 7 MPa for absorption). The eventual hydrogen storage capacity of Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4 together with FeTi has been found to be ∼5.0 wt%. To make the effect of catalysts intelligible, we have put forward in a schematic way the role of Li and Na borohydrides with FeTi for improving the hydrogen sorption properties of Mg(NH2)2–2LiH. [ABSTRACT FROM AUTHOR]

Exploitation of hydrogen as an energy carrier requires the development of systems for its storage and delivery. Formic acid has been proposed as valuable hydrogen carrier compound, due to its relatively high hydrogen content (53 g L−1), the latter being easily and cleanly released in catalytic reactions under mild conditions (HCOOH → H2 + CO2). Ionic liquids are interesting solvents for homogeneous catalyzed formic acid decomposition systems as their extremely low volatility avoids solvent contamination of the produced hydrogen stream. In this paper an outstandingly simple, robust and active catalyst system is presented, namely RuCl3 dissolved in 1-ethyl-2,3-dimethylimidazolium acetate (RuCl3/[EMMIM][OAc]). This system proved to be fully recyclable over 10 times. Turnover frequencies (TOF) of 150 h−1 and 850 h−1 were obtained at 80 °C and 120 °C, respectively. [ABSTRACT FROM AUTHOR]

Ag-based materials have features of low-cost and abundance in comparison with Pt-group metals, while their catalytic performance for hydrogen release from ammonia borane (AB) hydrolysis is relatively low. Herein, we report an activity improvement in hydrogen evolution from catalytic AB hydrolysis over a zeolitic imidazolate framework-67-derived Co@CN anchored Ag nanoparticle (NP) catalyst. Attributed to the rich N-dopant and spatial confinement of the Co@CN, small Ag NPs are uniformly distributed on the support (AgCo@CN). The obtained AgCo@CN exhibits excellent catalytic activity with a high turnover frequency of 282.8 min−1 for AB hydrolysis, outperforming most of the reported Ag-based catalysts and comparable to many Pt-group metal catalysts. The well-distributed Ag NPs with small sizes and the synergistic effect between Ag and Co@CN facilitate the oxidative cleavage of O–H in H2O molecules and thereby contribute to the boosted catalytic activity of AgCo@CN for AB hydrolysis. This strategy can be extended to synthesize other supported metal NPs with high efficiency for catalytic utilization. [ABSTRACT FROM AUTHOR]

CuS/Zn0.8Cd0.2S composites have been successfully prepared by simple hydrothermal and cation exchange method. The Cu species loaded on Zn0.8Cd0.2S, together with the intimate contact formed between CuS and Zn0.8Cd0.2S, was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. The optimized CuS/Zn0.8Cd0.2S photocatalyst has a high H2 evolution rate of 2792 μmol g−1 h−1 at CuS content of 3 wt% and the apparent quantum efficiency of 36.7% at 420 nm. The photophysical mechanism of the photocatalytic activity was investigated with the help of surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV) techniques. The results revealed that photogenerated charge separation efficiency in Zn0.8Cd0.2S was enhanced and the photogenerated electrons were trapped by the loaded CuS, which benefits photo-reduction. Those were the reasons for significant enhancement in the photocatalytic H2 evolution from water splitting. [ABSTRACT FROM AUTHOR]

NiCl2·6H2O ([Ni(H2O)6]2Cl2) per se does not show electrocatalytic hydrogen evolution reaction activity (HER) in an acidic aqueous medium as well as in neutral water. Interestingly, when [Ni(H2O)6]2+ is present in a polyoxovanadate matrix, for example, in the compound K2[Ni(H2O)6]2[V10O28]·4H2O (1), it exhibits homogeneous electrocatalytic HER activity in an acidic aqueous solution with a turn over frequency of 2.1 s−1 and an effective low overpotential of 127 mV at pH 2.3. Compound 1 is the first nickel-containing polyoxometalate catalyst for hydrogen production via homogeneous electrocatalytic proton reduction without its decomposition under electrochemical conditions of HER. [ABSTRACT FROM AUTHOR]

We demonstrate a lamellar NiMoCo@CuS catalyst, showing not only an excellent catalyst performance (η100@72 mV and a Tafel slope of 47 mV dec−1), but also a good stability (20 mA cm−2@30 hours), outperforming the NiMo system and noble Pt. [ABSTRACT FROM AUTHOR]

Lead-containing catalysts can be applied as solid “oxygen reservoirs” in a novel process for propane oxidative dehydrogenation. The catalyst lattice oxygen selectively burns hydrogen from the dehydrogenation mixture at 550 °C. This shifts the dehydrogenation equilibrium to the desired products side and can generate heat, aiding the endothermic dehydrogenation reaction. We compared the activity, selectivity and stability of three types of lead-containing solid oxygen reservoirs: alumina-supported lead oxide, lead-doped ceria, and lead chromate (PbCrO4). The first is active and selective, but not stable: part of the lead evaporates during the redox cycling. Stability studies of a biphasic material, consisting of doped ceria with a separate PbO phase, show that the PbO phase is not stabilised by the ceria. Evaporation of lead and segregation of lead from the doped ceria occurs during prolonged redox cycling (125 redox cycles at 550 °C, 73 h on stream). The activity of this catalyst does increase over time, which may be related to the segregation of lead. Segregation of lead into a separate phase also occurs when starting from lead-doped ceria (Ce0.92Pb0.08O2). The activity of this catalyst, however, does not increase with time on stream. Lead chromate (PbCrO4) shows the highest selectivity (∼100%) and activity (2.8 mol O kg−1) of all solid oxygen reservoirs tested (doped cerias, perovskites, and supported metal oxides). The activity is comparable to the theoretical maximum activity of CeO2(2.9 mol O kg−1). This activity does drop, however, during the first 60 redox cycles, to about 25% of the starting value, but this is still higher than the best results reported for doped cerias. [ABSTRACT FROM AUTHOR]

A process for a high yield of aromatics and co-produced hydrogen from the oxygen-free conversion of methane using a two-stage plasma-followed-by-catalyst (PFC) reactor at atmospheric pressure and low temperature is reported. Pure methane and a methane and hydrogen mixture as the feed gas for the two-stage PFC process were investigated, respectively. Using the methane and hydrogen mixture as the feed gas into the two-stage PFC reactor, Ni/HZSM-5 catalysts keep stable catalytic activity for a much longer on-stream time than that using pure methane as the feed gas. The maximum aromatic yield may be achieved using low Ni-loading Ni/HZSM-5 catalysts and at a suitable catalyst temperature. [ABSTRACT FROM AUTHOR]