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Comprehensive Summary For coordination‐insertion olefin polymerization, the development of novel transition‐metal catalysts has drawn extensive attention in this field. In this contribution, we designed a series of hemilabile α‐diimine nickel catalysts bearing oxygen atom as neighboring group. The steric hindrance and oxygen atom number of these nickel complexes (Ni1—Ni4) could be adjusted, which influenced ethylene (co)polymerization processes. The introduction of oxygen atoms could enhance the thermal stability during ethylene polymerization for Ni2 compared to the counterpart without oxygen atoms. And for the copolymerization process of ethylene with polar monomers, higher catalytic activity (1.4 × 106 g·mol−1·h−1) and polar monomer incorporation ratio (1.2 mol%) were achieved. However, Ni4 with four oxygen atoms in this work was not active in ethylene polymerization due to the interaction between the oxygen atom and nickel catalytic center. The hemilabile effect in this work presented an example to enhance the stability of the α‐diimine nickel catalysts in olefin polymerization. [ABSTRACT FROM AUTHOR]

Tremendous use of fossil fuels has raised a major concern of their depletion and various environmental issues hence research for its alternative came into the picture. Bio-diesel is one of the alternatives of fossil fuel and it is produced from vegetable feed-stock. The properties of the bio-diesel are similar to that of conventional fuel and thus it's widely used nowadays. Production of 100 kg bio-diesel generates 10 kg of glycerol as byproduct. Thus, to make the process more sustainable it's necessary to convert glycerol into useful product hydrogen. Steam reforming process is very efficient process in converting glycerol into renewable hydrogen since it is highly endothermic process and carried out at atmospheric pressure. The present work focuses on preparation of nickel-based catalysts using wet impregnation and co-precipitation methods and doping with promoters like zinc, magnesium on alumina support. Different techniques were employed for the characterization of synthesized catalysts, like XRD, SEM to know the physio-chemical properties of catalysts. 10% Ni/3% Zn/2% Mg/ A l 2 O 3 exhibited better results, 86% conversion of glycerol with hydrogen yield 78% at optimum conditions W/F = 15 kgcat s mole-1, T = 800 ∘ C, S/G = 9:1 ratio and at atmospheric pressure compared with 10% Ni/2% Mg/ A l 2 O 3 [ABSTRACT FROM AUTHOR]

A stagnation‐flow reactor was employed to investigate the decomposition of ammonia over a Ni/Al2O3 catalyst across a range of system pressures and ammonia mole fractions. The results indicate that the system pressure has a negligible impact on the light‐off behavior and the concentration profiles of NH₃. A comparison of 1D modelling with 3D computational fluid dynamics (CFD) computations justifies the use of the simpler flow model. Good agreement between experiments and the 1D simulation is achieved for two different kinetic models from literature in the mainly diffusion‐controlled regime. For lower temperatures, at which the process is kinetically controlled, the two mechanisms exhibit significant differences. The stagnation‐flow reactor concept is shown to be a promising tool for understanding, developing, and validating the reaction kinetics of heterogeneous catalytic processes. [ABSTRACT FROM AUTHOR]

The increase of antibiotic-resistant strains has necessitated the generation of antibacterial agents that do not induce microbial resistance. The present study was conducted to evaluate the antibacterial effect of copper-coated carbon nanotubes (Cu/CNTs) synthesized by plasma-enhanced chemical vapor deposition (PECVD) on two strains of gram positive (Staphylococcus aureus) and gram negative (Escherichia coli) bacteria. First, the PECVD method was used to deposit carbon nanotubes (CNTs) on high-resistivity silicon wafers previously decorated with nickel catalyst by an electron beam gun. These nanotubes were then coated with copper thin films (Cu, 0– 60 nm) in a vacuum evaporator using the Direct Current (DC) Magnetron Sputtering method. The morphology of PECVD-grown Cu/CNTs was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The antibacterial properties of as-synthesized Cu/CNTs against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were determined using Standard Plate Count (SPC). The results showed that increasing the coating thickness of Cu/CNTs had intensified their antibacterial activity. The SEM and TEM images confirmed the morphological modification of the samples after coating with copper. [ABSTRACT FROM AUTHOR]

The control of the regioselectivity of metal‐catalyzed α‐olefins polymerization is of everlasting interest. Most nickel and palladium catalysts show high regioselectivity involving 2,1‐insertion of α‐olefins and 1,ω‐enchainment chain‐straightening, especially α‐diimine nickel catalysts. In this contribution, we report extremely rare regioselective chain‐straightening polymerization of α‐olefins through 2,ω‐enchainment using unsymmetrical amine–imine nickel catalysts. The polymerizations of α‐olefins (1‐hexene, 1‐octene, and 1‐decene) were studied in detail, and the effects of catalyst structure, reaction temperature, and monomer concentration on the polymerization activity and the regioselectivity were examined. The unsymmetrical N‐substituents of the amine–imine nickel catalysts play a crucial role in the regioselectivity. High regioselectivity involving 80.4% 1,2‐insertion and 84.5% 2,ω‐enchainment is realized to produce amorphous polyolefins without melting temperatures. [ABSTRACT FROM AUTHOR]

This study investigates the impact of cerium promotion on NiMgAl catalysts for methane dry reforming (DRM) at 750 °C. A series of NiMgAl-Ce oxides with varying cerium content NiMgAlCe-x (x: rate of substitution of aluminium by cerium) were synthesized via co-precipitation method, aiming to enhance catalytic activity through the incorporation of nickel into hydrotalcite structures and cerium promotion. The obtained systems calcined at 800 °C, reduced at 750 °C and used catalysts were characterized by ICP, BET, XRD, SEM, H2-TPR, TPO and O2-TG analysis. The results demonstrate that cerium content influences specific surface area, with higher cerium promoting increased surface area but hindering catalytic activity and improved carbon resistance of the catalysts.. Activity improved with reaction temperature, with NiMgAl achieving the highest conversion, with CH4 conversion dropping from 16% at 450 °C to 95.0% at 750°C. Stability tests at 750 °C, revealed decreased activity in cerium-containing catalysts. On the other hand in the case of catalysts without prior reduction, the catalytic activity of NiMgAlCe-1 and NiMgAlCe-2 catalysts are better, however, the NiMgCe solid presents a total catalytic inertia. This result suggests that the presence of aluminium is bringing a Lewis acidity favours this reducibility suggesting an influence on redox behaviour. Carbon fibers formation was observed, but it did not significantly affect reactor performance. [ABSTRACT FROM AUTHOR]

This review underscores the pivotal role that nickel-based catalysts play in advancing CO2 methanation technologies, which are integral to achieving carbon neutrality. This study meticulously examines various aspects of catalyst design, including the significance of support materials and co-catalysts in enhancing catalytic activity and selectivity. This discussion reveals that while nickel catalysts offer a cost-effective solution due to their availability and high performance, challenges such as sintering and carbon deposition at high temperatures remain. These issues necessitate the development of catalysts with superior thermal stability or those capable of maintaining high activity at lower temperatures. This review also highlights the innovative use of three-dimensional fiber deposition technology in fabricating catalysts, which has shown promising results in improving reaction efficiency and stability over prolonged operation. Moving forward, this research emphasizes the importance of optimizing catalyst structure and fabrication techniques to overcome existing limitations. The ongoing development in this field holds great promise for the industrial application of CO2 methanation, contributing significantly to global efforts in reducing greenhouse gas emissions and promoting sustainable energy use. [ABSTRACT FROM AUTHOR]

The search for alternative non‐noble transition metal catalysts able to evolve hydrogen has been the focus of intense research. Molecular complexes bearing redox‐active ligands have been reported as efficient electrocatalysts for hydrogen evolution reaction (HER). This study showcases a new family of nickel‐thiosemicarbazone complexes displaying significant activity for HER in DMF solvent using trifluoracetic acid as proton source. Following previous works in our group, the ligand was stereochemically tailored, placing methoxy groups at different locations and considering various combinations of positions. Three complexes within the series were shown to outperform the parent catalyst bearing the methoxy group in para position. Overall, the nickel catalyst having the chemical substituent in meta position displays the best catalytic performances while having the lowest overpotential. These results support that ligand stereochemical tailoring in metal complexes improves electrocatalytic HER and suggest that ligand tuning is a promising direction to enhance catalyst performances. [ABSTRACT FROM AUTHOR]

Olefin polymerization is one of the most important chemical reactions in industry. This work presents a strategy that emphasizes the synergistic meta/para-steric hindrance of N-aryl groups and electronic effects in newly synthesized neutral salicylaldiminato nickel catalysts. These nickel(II) catalysts exhibit exceptional thermostability, ranging from 30 °C to 130 °C, demonstrating enhanced catalytic activities and broadly regulated polyethylene molecular weights (3–341 kg·mol−1) and controlled polymer branch density (2–102 brs/1000C). The preferred catalyst Ni3 with concerted steric and electronic effects enables the production of solid-state semi-crystalline polyethylene materials at temperatures below 90 °C. Notably, Ni3 exhibits an impressive tolerance of 110 °C and can withstand even the challenging polymerization temperature of 130 °C, leading to the production of polyethylene wax and oil. Also, functionalized polyethylene is produced. [ABSTRACT FROM AUTHOR]

Context: This study investigates the ethylene insertion reaction mechanism for polymerization catalysis, aiming to discern differences between Ni-α-imine ketone–type catalyst and their SiO2-supported counterpart. The reaction force analysis unveils a more intricate mechanism with SiO2 support, shedding light on unexplored factors and elucidating the observed lower catalytic activity. Furthermore, reactivity indexes suggest earlier ethylene activation in the supported catalyst, potentially enhancing overall selectivity. Finally, the reaction electronic flux analysis provides detailed insights into the electronic activity at each step of the reaction mechanism. In sum, this study offers a comprehensive understanding of the ethylene insertion reaction mechanism in both molecular and supported catalysts, underscoring the pivotal role of structural and electronic factors in catalytic processes. Methods: Density functional theory (DFT) calculations were conducted using the ωB97XD functional and the 6–31 + G(d,p) basis sets with Gaussian16 software. Computational techniques utilized in this study encompassed the IRC method, reaction force analysis, and evaluation of electronic descriptors such as electronic chemical potential, molecular hardness, and electrophilicity reactivity indexes. Additionally, reaction electronic flux analysis was employed to investigate electronic activity along the reaction coordinate. [ABSTRACT FROM AUTHOR]

The aim of this study was to deposit a Ni–La–Zr catalyst on a FeCrAl monolith by in situ growth of the catalyst on a metallic surface through immersion in a modified polymeric precursor solution. The prepared monolith was characterized by X-ray diffraction, atomic force microscopy, and scanning electron microscopy and was tested in a tri-reforming reaction of simulated biogas (CH4/CO2 = 3) for synthesis gas production. The monolithic catalyst presented better stability than the powdered catalyst under the 50-h test. In contrast, the powdered catalyst showed more pronounced deactivation, which was associated with higher carbon deposition. This study provides valuable information on a simple deposition method for Ni-based catalysts on FeCrAl monoliths for biogas tri-reforming reactions, which could have implications for biogas upgrading. [ABSTRACT FROM AUTHOR]

It has been shown that the nature of the metal precursor and the thermal effects during calcination determine the physicochemical properties of the catalysts and their catalytic activity in the levulinic acid (LA) and 5-hydroxymethylfurfural (HMF) hydrogenation reactions. The endothermic effect during calcination of the inorganic nickel precursor promoted higher metal dispersion and stronger interaction with the alumina surface. In contrast, the exothermic effects during the calcination of organic nickel precursors resulted in smaller metal dispersion and lower interaction with the support surface. A clear relationship was found between the size of the metal crystallites and the yield of LA hydrogenation reaction. The smaller crystallites were more active in the LA hydrogenation reaction. In turn, the size of the metal particles and their nature of interaction with the surface of the alumina influence the hydrogenation pathways of the HMF. [ABSTRACT FROM AUTHOR]

The development of highly active, reusable catalysts for aqueous‐phase reactions is challenging. Herein, metallic nickel is encapsulated in a nitrogen‐doped carbon–silica composite (SiO2@Ni@NC) as a catalyst for the selective hydrogenation of vanillin in aqueous media. The constructed catalyst achieved 99.8% vanillin conversion and 100% 4‐hydroxymethyl‐2‐methoxyphenol selectivity at room temperature. Based on combined scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, and Raman analyses, the satisfactory catalytic performance is attributed to the composite structure consisting of an active metal, carbon, and silica. The hydrophilic silica core promoted dispersion of the catalyst in aqueous media. Moreover, the external hydrophobic NC layer has multiple functions, including preventing oxidation or leaching of the internal metal, acting as a reducing agent to reduce the internal metal, regulating the active‐site microenvironment by enriching the concentrations of H2 and organic reactants, and modifying the electronic structure of the active metal via metal–support interactions. Density functional theory calculations indicated that NC facilitates vanillin adsorption and hydrogen dissociation to promote aqueous‐phase hydrogenation. This study provides an efficient strategy for constructing encapsulated Ni‐based amphiphilic catalysts to upgrade biomass‐derived compounds. [ABSTRACT FROM AUTHOR]

Hydrocarbons, when used as the medium for transition metal catalyzed organic reactions and olefin (co‐)polymerization, are ubiquitous. Environmentally friendly water is highly attractive and long‐sought, but is greatly challenging as coordination‐insertion copolymerization reaction medium of olefin and polar monomers. Unfavorable interactions from both water and polar monomer usually lead to either catalyst deactivation or the formation of low‐molecular‐weight polymers. Herein, we develop well‐behaved neutral phosphinophenolato nickel catalysts, which enable aqueous copolymerization of ethylene and diverse polar monomers to produce significantly high‐molecular‐weight linear polar polyolefins (219–549 kDa, 0.13–1.29 mol %) in a single‐component fashion under mild conditions for the first time. These copolymerization reactions occur better in water than in hydrocarbons such as toluene. The dual characteristics of high molecular weight and the incorporation of a small amount of functional group result in improved surface properties while retain the desirable intrinsic properties of high‐density polyethylene (HDPE). [ABSTRACT FROM AUTHOR]

In this study, vermiculite was explored as a support material for nickel catalysts in two key processes in syngas production: dry reforming of methane with CO2 and steam reforming of ethanol. The vermiculite underwent acid or base treatment, followed by the preparation of Ni catalysts through incipient wetness impregnation. Characterization was conducted using various techniques, including X-ray diffraction (XRD), SEM–EDS, FTIR, and temperature-programmed reduction (H2-TPR). TG-TD analyses were performed to assess the formation of carbon deposits on spent catalysts. The Ni-based catalysts were used in reaction tests without a reduction pre-treatment. Initially, raw vermiculite-supported nickel showed limited catalytic activity in the dry reforming of methane. After acid (Ni/VTA) or base (Ni/VTB) treatment, vermiculite proved to be an effective support for nickel catalysts that displayed outstanding performance, achieving high methane conversion and hydrogen yield. The acidic treatment improved the reduction of nickel species and reduced carbon deposition, outperforming the Ni over alkali treated support. The prepared catalysts were also evaluated in ethanol steam reforming under various conditions including temperature, water/ethanol ratio, and space velocity, with acid-treated catalysts confirming the best performance. [ABSTRACT FROM AUTHOR]

This study describes a method to synthesize compounds with an arylidene group at the alpha position of N‐methyl‐2‐pyrrolidone (NMP) and an alcohol group at the gamma position in a single‐step reaction using NMP and aldehyde. The highest yields were obtained with Ni(glyme)Cl2 as a nickel catalyst and tert‐butyl hydroperoxide as the oxidant, and various aryl aldehydes reacted under optimal conditions to yield the target compounds. [ABSTRACT FROM AUTHOR]

An efficient and versatile synthesis of alcohols via transfer hydrogenation from ketones with isopropanol, utilizing [Ni(6,6′‐(OH)2‐2,2′‐bpy)][Br2] under alkaline conditions, has been documented. It was noteworthy that many readily reducible or labile functional groups such as nitro, cyano, and halide, within the same molecular framework, did not undergo any change under the standard reaction conditions. Furthermore, the gram scale transfer hydrogenation reaction was successfully carried out with good yield using a common route with only a single purification by column chromatography. [ABSTRACT FROM AUTHOR]

The physical properties of traditional polyolefin materials can be significantly improved by introducing polar groups, especially polar aromatic groups. However, it remains a major challenge to realize the highly effective copolymerization of ethylene with styrene derivatives. In this study, the direct copolymerization of ethylene with various polar styrene monomers bearing functional groups (o‐OMe, m‐OMe, p‐OMe, o‐Cl, m‐Cl, p‐ClSt, o‐F, o‐Br, p‐Me, p‐Ph, p‐Vinyl, p‐COOH, and C6F5) was achieved using phosphino‐dihydronaphtholate neutral nickel catalysts Ni1‐Ni3. Additionally, the catalytic behavior and the applicability of the polar monomer were evaluated in detail by copolymerization results. Catalysts Ni1‐Ni3 demonstrated inactivity towards the polymerization of polar styrene monomers but exhibited moderate catalytic activities in the copolymerization of ethylene with polar styrene monomers, yielding moderate‐molecular‐weight (Mw > 10 kDa) copolymers with the polar monomer contents ranging from 1.32 to 4.16 mol%. The steric and electronic effects of the substituent depending on the types and position in the phenyl ring considerably influenced the copolymerization behavior. Furthermore, comprehensive NMR analyses of the produced copolymers revealed that the polar monomers formed in‐chain insertions, saturated chain ends, and unsaturated chain ends after incorporation. [ABSTRACT FROM AUTHOR]

CO2 methanation is one of the advantageous processes of carbon capture and utilisation (CCU) technologies to circulate the carbon on Earth, mitigating the release and loss of CO2 into the atmosphere. Herein, a Ni/r-CeO2 catalyst was fabricated using a facile method of impregnating Ni(NO3)2·6H2O on CeO2 nanorods (r-CeO2), synthesised by hydrothermal method at low temperature (130 °C). The influence of Ni active phase content and activation condition on the characteristics and catalytic performances in CO2 methanation were investigated. The physicochemical properties of the synthesised catalyst were studied using several techniques: XRD, EDS, isotherm nitrogen adsorption, SEM, HR-TEM, H2-TPR, CO2-TPD and Raman. Catalytic activity survey and analysis show the excellent performance of Ni/r-CeO2 with a Ni loading of 15 wt% (15NiCe) calcined at 600 °C for 4 h and reduced at 450 °C for 2.5 h. By adjusting the nickel loading on ceria and altering synthesis conditions, it's possible to achieve highly dispersed NiO particles with an optimal size (∼13.9 nm), abundant oxygen vacancies, and the presence of medium-strength basic sites. This leads to improved catalytic activity, resulting in an equilibrium CO2 conversion rate of approximately 90% and 100% selectivity for CH4 at temperatures as low as 325°C. The 15Ni/r-CeO2 catalyst serves as a highly active low-temperature catalyst for CO2 methanation.

The homopolymerization of norbornene and the copolymerization of norbornene and ethylene were carried out using the neutral α-sulfonate-β-diimine nickel catalyst SD-Ni. The neutral α-sulfonate-β-diimine catalyst is highly active in the homopolymerization of norbornene, producing vinyl-addition polynorbornene (PNB) with a high molecular weight. The copolymerization of norbornene (NB) and ethylene (E) using the catalyst SD-Ni was also investigated. The α-sulfonate-β-diimine catalyst SD-Ni shows distinctive catalytic copolymerization properties to produce high-molecular-weight E-NB copolymers with low norbornene incorporation. Importantly, microstructure analyses confirm that the resultant E-NB copolymers are branched cyclo-olefin copolymers (COCs) with branched polyethylene units.

Biomass valorization is an essential strategy for converting organic resources into valuable energy and chemicals, contributing to the circular economy, and reducing carbon footprints. Glycerol, a byproduct of biodiesel production, can be used as a feedstock for a variety of high-value products and can contribute to reducing the carbon footprint. This study examines the impact of surface-level modifications of Mg, Cu, and Sn on Ni-Ce-Zr catalysts for the hydrogenolysis of glycerol, with in situ generated hydrogen. The aim of this approach is to enhance the efficiency and sustainability of the biomass valorization process. However, the surface modification resulted in a decrease in the global conversion of glycerol due to the reduced availability of metal sites. The study found that valuable products, such as H2 and CH4 in the gas phase, and 1,2-PG in the liquid phase, were obtained. The majority of the liquid fraction was observed, particularly for Cu- and Sn-doped catalysts, which was attributed to their increased acidity. The primary selectivity was towards the cleavage of the C–O bond. Post-reaction characterizations revealed that the primary causes of deactivation was leaching, which was reduced by the inclusion of Cu and Sn. These findings demonstrate the potential of Cu- and Sn-modified Ni-Ce-Zr catalysts to provide a sustainable pathway for converting glycerol into value-added chemicals. [ABSTRACT FROM AUTHOR]

[Display omitted] Manipulating metal valence states and porosity in the metal–organic framework (MOF) by alloying has been a unique tool for creating high-valent metal sites and pore environments in a structure that are inaccessible by other methods, favorable for accelerating the catalytic activity towards sensing applications. Herein, we report Fe3+-driven formation of catalytic active Ni3+ species in the amine-crafted benzene-dicarboxylate (BDC-NH 2)-based MOF as a high-performance electrocatalyst for glucose sensing. This work took the benefit of different bonding stability between BDC-NH 2 ligand, and Fe3+ and Ni2+ metal precursor ions in the heterometallic Ni x Fe (1- x) -BDC-NH 2 MOF. The FeCl 3 that interacts weakly with ligand, oxidizes the Ni2+ precursor to Ni3+-based MOF owing to its Lewis acidic behavior and was subsequently removed from the structure supported by Ni atoms, during solvothermal synthesis. This enables to create mesopores within a highly stable Ni-MOF structure with optimal feed composition of Ni 0.7 Fe 0.3 -BDC-NH 2. The Ni3+-based Ni 0.7 Fe 0.3 -BDC-NH 2 demonstrates superior catalytic properties towards glucose sensing with a high sensitivity of 13,435 µA mM−1 cm−2 compared to the parent Ni2+-based Ni-BDC-NH 2 (10897 μA mM−1 cm−2), along with low detection limit (0.9 μM), short response time (≤5 s), excellent selectivity, and higher stability. This presented approach for fabricating high-valent nickel species, with a controlled quantity of Fe3+ integrated into the structure allowing pore engineering of MOFs, opens new avenues for designing high-performing MOF catalysts with porous framework for sensing applications. [ABSTRACT FROM AUTHOR]

With the increasing demand for production of graphitic materials for various applications, it becomes crucial to get a fundamental understanding of how graphene layers grow on metal catalysts. Here, we performed an in situ heating transmission electron microscopy (TEM) study to understand the mechanism of graphitization of amorphous carbon (a-C) on Ni catalyst by following graphene growth at atomic resolution in real time. By discerning the Ni3C phase from the pure Ni phase during the graphitic carbon growth process, we demonstrate that growth occurs through the carbide graphitization of Ni3C. Additionally, during the graphitization, Ni diffusion has a crucial effect on the structure of the resulting graphene. Under our experimental conditions, we observed graphene contains islands of multilayers. Based on our in situ experimental results, we suggest a mechanism for graphitization of the a-C/Ni system and explain the dynamics resulting from Ni diffusion. Our study can contribute to the control of graphitization by using Ni catalyst in the production of graphene and other graphitic materials.

In classic cyanation reactions, toxic metal cyanide sources or complex organic cyanide sources are often used. Therefore, it is particularly important to develop a green and economical cyano source. Initially, 4-biphenylyl trifluoromethanesulfonate is chosen as the model substrate. Through extensive screening of catalysts, ligands, additives, reductant, temperature and other conditions, the optimal conditions are obtained (Ni(OTf)2, 1, 3-bis (diphenyphosphino)propane, Zn(OTf)2, Zn with a mole fraction of 0.1, 0.1, 0.2, 2, respectively, 0.7 mL CH3CN, N2, 60 h, 100 ℃). Subsequently, the generation and limitations of the substrates are studied under optimal conditions. It is found that substrates bearing electron-donating substituents exhibit an excellent efficiency for the cyanation of aryl trifluoromethanesulfonates. The cyanation of aryl trifluoromethanesulfonates is first realized under the catalysis of nickel with acetonitrile as a green and economical cyano source.

Objectives. To take into account the change in the number of active sites during the adsorptioncatalytic deformation and deactivation of a catalyst surface by means of a catalytic poison when calculating the turnover frequency (TOF) of a hydrogenation catalyst.Methods. The activity was determined by a static method, using a titanium reactor having a volume of 400 mL, an experimental temperature controlled using a liquid thermostat with an accuracy of 0.5 K, with a paddle stirrer rotation speed of 3600 rpm and system hydrogen pressure equal to atmospheric. The consumption of hydrogen used to reduce the model compound was taken into account via the volumetric method. The heats of hydrogen adsorption were determined using a reaction calorimeter with an operating mode close to that of a chemical reactor. After measuring the specific surface area using low temperature nitrogen adsorption, the results were processed using Brunauer–Emmett–Teller theory approximations. Deactivation was carried out by introducing dosed amounts of catalytic poison into the system in titration mode.Results. A kinetic experiment for the reduction of a multiple carbon bond in a sodium maleate molecule using aqueous solutions of sodium hydroxide with additions of monohydric aliphatic alcohols as solvents under conditions of partial deactivation of the catalyst was carried out. The obtained values of heats of hydrogen adsorption on skeletal nickel in the course of the experiment are given. The described approach is used to calculate TOF values taking into account changes in the number of active surface sites during the course of a catalytic reaction and upon the introduction of a deactivating agent. A refined equation for the correct calculation of TOF is proposed along with its mathematical justification. The results of TOF calculations under various assumptions for a number of catalytic systems are shown.Conclusions. When calculating absolute activity values, a change in the number of active sites has a significant effect on the obtained values. The physical meaning of a number of constants in the proposed equation relates the activity of the catalyst to the distribution of hydrogen on its surface in terms of heats of adsorption.

Ni/Al2O3 catalysts (noted as Ni/Al-350, Ni/Al-500, and Ni/Al-700, respectively) were synthesized by a facile solution combustion method but at different combustion temperatures (350 °C, 500 °C, and 700 °C, respectively). For comparison, Ni/Al2O3 (noted as Ni/Al-100) was also prepared by the impregnation method and applied in the methanation reaction. The Ni/Al2O3 synthesized at the combustion temperature of 350 °C showed better performance than the others at higher combustion temperatures, and the activity for CO2 methanation followed an order of Ni/Al-350 > Ni/Al-500 > Ni/Al-700 > Ni/Al-100. The increase in the combustion temperature decreased active sites for the H2 and CO2 adsorption, which could be associated with the reduced Ni dispersion and basic sites, thus lowering its activity and increasing its carbon deposition rate.

In the presented work, the catalytic performance of a nickel catalyst, in CO2 hydrogenation to methane, within a ZrO2 open-cell foam (OCF)-based catalyst was studied. Two series of analogous samples were prepared and coated with 100–150 mg of a Mg-Al oxide interface to stabilize the formation of well-dispersed Ni crystallites, with 10–15 wt% of nickel as an active phase, based on 30 ppi foam or 45 ppi foam. The main factor influencing catalytic performance was the geometric parameters of the applied foams. The series of catalysts based on 30 ppi OCF showed CO2 conversion in the range of 30–50% at 300 °C, while those based on 45 ppi OCF resulted in a significantly enhancement of the catalytic activity: 90–92% CO2 conversion under the same experimental conditions. Calculations of the internal and external mass transfer limitations were performed. The observed difference in the catalytic activity was primarily related to the radial transport inside the pores, confirmed with the explicitly higher conversions. [ABSTRACT FROM AUTHOR]

Solar‐driven photothermal conversion of carbon dioxide (CO2) to methane (CH4) is a promising approach to remedy energy shortage and climate changes, where highly efficient photothermal catalysts for CO2 methanation urgently need to be designed. Herein, nickel‐based catalysts (Ni/ZrO2) derived from metal–organic frameworks (MOFs) are fabricated and studied for photothermal CO2 methanation. The optimized catalyst 50Ni/ZrO2 achieves a stable CH4 production rate of 583.3 mmol g−1 h−1 in a continuous stability test, which is almost tenfold higher than that of 50Ni/C‐ZrO2 synthesized via commercial ZrO2. Physicochemical properties indicate that 50Ni/ZrO2 generates more tetragonal ZrO2 and possesses more oxygen vacancies (OVs) as well as enhanced nickel‐ZrO2 interaction. As a result, 50Ni/ZrO2 exhibits the strong abilities of light absorption and light‐to‐heat conversion, superior adsorption capacities of reactants (H2, CO2), and an intermediate product (CO), which finally boosts CH4 formation. This work provides an efficient strategy to design a photothermocatalyst of CO2 methanation through utilizing MOFs‐derived support. [ABSTRACT FROM AUTHOR]

This study investigates the effect of cerium–zirconium supported nickel catalyst (Ni/CeZr(x)) on the dry reforming reaction of methane (CH4) and carbon dioxide (CO2) to produce hydrogen (H2) and carbon monoxide (CO) for use in petrochemical processes. CeZr supports were synthesized via template-assisted co-precipitation using CTAC as a template with varying pH values (5, 7, 8.5, and 10) and underwent hydrothermal processing. Nickel (10% by weight) was then loaded onto the support through incipient wetness impregnation. The dry reforming reaction was performed at 700 °C. Results revealed that as the pH increased from acidic to basic conditions, the precipitation and integration of ZrO2 and CeO2 improved, leading to the formation of CeZr(x) composite supports. The Ce/Zr ratio in Ni/CeZr(x) catalysts influenced the generation of oxygen vacancies (OV) on the catalyst surface, affecting CO2 and CH4 conversions and the H2/CO ratio. The Ni/CeZr(8.5) catalyst exhibited the highest activity and stability due to its high surface oxygen vacancy and the number of basic sites on the CeZr(8.5) surface. Moreover, this catalyst reduced coke formation by promoting CO2 adsorption and dissociation, which facilitated the formation of surface-bound oxygen species that reacted with the surface carbon species. [ABSTRACT FROM AUTHOR]

Syngas can be produced from biomethane via Partial Oxidation of Methane (POM), being an attractive route since it is ecofriendly and sustainable. In this work, catalysts of Ni supported on MgO–ZrO2 solid solutions, prepared by a one-step polymerization method, were characterized by HRTEM/EDX, XRD, XPS, H2-TPR, and in situ XRD. All catalysts, including Ni/ZrO2 and Ni/MgO as reference, were tested for POM (CH4:O2 molar ratio 2, 750 ºC, 1 atm). NiO/MgO/ZrO2 contained two solid-solutions, MgO–ZrO2 and NiO-MgO, as revealed by XRD and XPS. Ni (30 wt%) supported on MgO–ZrO2 solid solution exhibited high methane conversion and hydrogen selectivity. However, depending on the MgO amount (0, 4, 20, 40, 100 molar percent) major differences in NiO reducibility, growth of Ni0 crystallite size during H2 reduction and POM, and in carbon deposition rates were observed. Interestingly, catalysts with lower MgO content achieved the highest CH4 conversion (~ 95%), high selectivity to H2 (1.7) and CO (0.8), and low carbon deposition rates (0.024 g carbon.gcat−1 h−1) with Ni4MgZr (4 mol% MgO) turning out to be the best catalyst. In situ XRD during POM indicated metallic Ni nanoparticles (average crystallite size of 31 nm), supported by MgO–ZrO2 solid solution, with small amounts of NiO–MgO being present as well. The presence of MgO also influenced the morphology of the carbon deposits, leading to filaments instead of amorphous carbon. A combustion-reforming mechanism is suggested and using a MgO–ZrO2 solid solution support strongly improves catalytic performance, which is attributed to effective O2, CO2 and H2O activation at the Ni/MgO–ZrO2 interface. [ABSTRACT FROM AUTHOR]

A major cause of premature catalyst deactivation in the catalytic hydrogenation of fatty acids is the presence of impurities in the feedstock. With more oleochemical plants shifting to opportunistic crude palm oil (CPO) as their feedstock, the feedstock quality becomes an important factor in their procurement process. For CPO, the impurities level can be coarsely estimated by the deterioration of bleaching index (DOBI). A high DOBI value (e.g. DOBI > 2.99) indicates good quality CPO and ease in processing, while low DOBI value implies low level of carotene and/or high level of oxidised sludge oil, both of which could be detrimental to the processing of CPO. In our work, unsplit CPO feedstocks with varying DOBI value were directly hydrogenated in a laboratory‐scale pressure reactor with the presence of commercial nickel catalysts. Experimental results showed that catalyst deactivation was linked to DOBI value, where decreasing DOBI led to faster catalyst deactivation. For example, iodine value (IV) < 1.0 can be achieved for CPO with high DOBI value (2.97) after 150 min, and IV of 5–7 and IV > 20 were achieved for medium DOBI value (2.57–2.68) and low DOBI value (2.24), respectively. For CPO with low DOBI value (2.24), doubling the catalyst dosage ensured that the hydrogenated product met the low IV specification. This work showed that identifying the CPO with DOBI value presents an indicator to the manufacturer to find the right CPO tailored to the existing processes to maximise profitability. [ABSTRACT FROM AUTHOR]

Rate-controlled growth of carbon nanotubes (CNTs) and catalyst design are considered efficient ways for the preparation of CNTs with specific structures and properties. However, due to the difficulties in capturing the growth process of the CNTs with tiny size under a complex growth environment, the growth kinetics of CNTs and their correlation with the catalyst seed have been seldom revealed. Here, we investigated the growth process of CNTs from Ni nanoparticles (NPs) in real-time under atmospheric pressure using transmission electron microscopy equipped with a closed gas cell. It was found that the growth rates of CNTs fluctuated, and a phase transition from Ni3C to Ni, and a reshaping of the catalyst NPs occurred during the growth process. We demonstrated that CNTs dynamically interacted with the connected catalyst NPs and the fluctuated growth rates of CNTs were correlated with the structure change of catalyst NPs. The origin of the growth rate fluctuation is attributed to the change of carbon concentration gradient in catalyst NPs. [ABSTRACT FROM AUTHOR]

Abstract Barium doping effect on the activity and stability of nickel‐based catalysts, supported on yttria‐stabilized zirconia (Ni‐YZr), was investigated in dry reforming of methane. Catalysts were characterized by several techniques (nitrogen sorption, X‐ray diffraction [XRD], scanning electron microscopy with energy dispersive X‐ray, transmission electron microscopy [TEM], thermogravimetric analysis [TGA], temperature programmed oxidation, CO2‐TPD, H2‐TPR) and were tested in a fixed‐bed reactor at 800°C and 42,000 mL/h gcat. Barium played a crucial role in enhancing catalyst reducibility and CO2 adsorption at high temperatures, as indicated by the activity and stability of the Ni‐YZr catalyst. The addition of 4.0 wt% of barium appeared to be the optimal loading, allowing for CH4 conversion of 82%, which remained constant for 7 h of reaction, compared with 72% of barium‐unpromoted Ni‐YZr at 800°C. TEM images of the spent catalysts revealed the formation of multiwalled carbon nanotubes on all samples. The TGA analysis showed, however, that an increase in baria loading significantly reduced the coke formation amount, indicating the inhibition of coke formation and the enhancement of the catalytic activity. Such improvement in activity and stability was attributed to the incorporation of barium into YZr support, as revealed by XRD analysis, which inhibited the sintering of the catalysts support.

[Display omitted] • Two fluorinated and one non–fluorinated complex of the type [(NHC)Ni(Cp)(Br)] were synthesized and characterized. • The non–fluorinated complex showed higher catalytic activity than the fluorinated ones in the C–S cross–coupling reaction. • The catalytic reaction mechanism was studied by theoretical calculations. • Strong nucleophilic substrates quenched the C–S cross–coupling by forming a stable intermediate complex. The catalytic activities of three Ni(II) complexes with fluorinated and non–fluorinated N–heterocyclic carbene (NHC) ligands were evaluated in the C–S cross–coupling reaction between iodobenzene and thiophenol. The complexes with fluorinated–NHC ligands exhibited lower catalytic activities compared to the non–fluorinated derivative. This can be attributed to the lower electron–donating character of the fluorinated ligands in comparison to the non–fluorinated ligand. Complex 3–Ni was tested towards different substrates, achieving moderate to good conversions. Additionally, the reaction mechanism of the C–S cross–coupling using two substrates, tert–butylthiol and 2,4–dichlorobenzenethiol, was determined. Tert–butylthiol produced a stable intermediate that inhibited the last step of the reaction mechanism (reductive elimination). On the other hand, 2,4–dichlorobenzenethiol formed a less stable intermediate, favoring the reductive elimination. This observation aligns with the lower yield observed when using tert–butylthiol compared to 2,4–dichlorobenzenethiol (20% vs 99%). [ABSTRACT FROM AUTHOR]

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Application of bioisostere plays an important role in drug discovery. α‐Aminoboronic acid is the familiar bioisostere of α‐amino acid. Developing reactions for the synthesis of a wide variety of α‐aminoboronic acid is one important task for synthetic chemistry. Herein, we report the development of nucleophilic C‐borylation chemistry for N‐arylimines catalyzed by nickel. The reaction proceeds through the insertion of a borylnickel species into the C=N bond to afford the corresponding α‐aminoboronate, which was isolated as acetamide after trapping with acetic anhydride. N‐Benzyl imine is also tolerated by the developed reaction. [ABSTRACT FROM AUTHOR]

SP 1 sp H NMR (400 MHz, CDCl SB 3 sb ): = 8.09 (d, I J i = 8.7 Hz, 1 H), 7.77 (d, I J i = 8.0 Hz, 1 H), 7.69 (d, I J i = 8.8 Hz, 1 H), 7.49 (t, I J i = 7.3 Hz, 1 H), 7.38-7.30 (m, 2 H), 4.32 (s, 1 H), 3.86-3.63 (m, 2 H), 3.22-3.14 (m, 1 H), 3.14-3.03 (m, 1 H), 3.00 (s, 3 H), 2.72-2.58 (m, 2 H), 2.14-1.97 (m, 2 H), 1.71 (t, I J i = 12.7 Hz, 1 H), 1.66-1.57 (m, 1 H), 1.04 (t, I J i = 7.1 Hz, 3 H). SP 1 sp H NMR (400 MHz, CDCl SB 3 sb ): = 6.97 (d, I J i = 7.8 Hz, 1 H), 6.84 (d, I J i = 9.7 Hz, 2 H), 4.10-3.91 (m, 2 H), 3.25 (p, I J i = 6.0 Hz, 1 H), 3.03-2.85 (m, 2 H), 2.82 (s, 3 H), 2.71 (t, I J i = 11.9 Hz, 1 H), 2.51-2.38 (m, 1 H), 2.27 (s, 3 H), 1.93-1.68 (m, 3 H), 1.60 (d, I J i = 13.1 Hz, 1 H), 1.23 (t, I J i = 7.0 Hz, 3 H). SP 1 sp H NMR (400 MHz, CDCl SB 3 sb ): = (isomer 1) = 7.18 (q, I J i = 7.9 Hz, 1 H), 7.11-7.05 (m, 1 H), 6.98-6.87 (m, 2 H), 4.93 (ddd, I J i = 49.2, 7.8, 4.9 Hz, 1 H), 4.23-4.09 (m, 2 H), 3.34-3.25 (m, 1 H), 3.02-2.91 (m, 1 H), 2.90-2.79 (m, 1 H), 2.85 (s, 3 H), 2.79-2.62 (m, 1 H), 2.51-2.29 (m, 1 H), 1.85-1.72 (m, 2 H), 1.71-1.58 (m, 2 H), 1.28 (t, I J i = 7.1 Hz, 3 H); (isomer 2) = 7.18 (q, I J i = 7.8 Hz, 1 H), 7.11-7.05 (m, 1 H), 6.98-6.87 (m, 2 H), 4.54 (ddd, I J i = 49.8, 10.7, 2.6 Hz, 1 H), 4.23-4.09 (m, 2 H), 3.34-3.25 (m, 1 H), 3.02-2.91 (m, 1 H), 2.90-2.79 (m, 1 H), 2.84 (s, 3 H), 2.51-2.29 (m, 1 H), 2.06-1.92 (m, 1 H), 1.85-1.72 (m, 2 H), 1.71-1.58 (m, 2 H), 1.27 (t, I J i = 7.1 Hz, 3 H). SP 1 sp H NMR (400 MHz, CDCl SB 3 sb ): = 7.17 (dd, I J i = 8.5, 2.0 Hz, 1 H), 7.07 (d, I J i = 2.0 Hz, 1 H), 6.71 (d, I J i = 8.5 Hz, 1 H), 4.01 (q, I J i = 7.0 Hz, 2 H), 3.18 (p, I J i = 5.3 Hz, 1 H), 2.95-2.76 (m, 2 H), 2.73 (s, 3 H), 2.72-2.63 (m, 1 H), 2.38-2.25 (m, 1 H), 1.78-1.60 (m, 3 H), 1.59-1.50 (m, 1 H), 1.19 (t, I J i = 7.1 Hz, 3 H). [Extracted from the article]

Ni and Co catalysts supported on ITQ-6 zeolite have been synthesized and evaluated in the steam reforming of ethanol (SRE). Catalysts were also characterized by means of N 2 adsorption-desorption, XRD, H 2 -TPR, and H 2 -chemisorption. ITQ-6 containing Co (Co/ITQ-6) presented a higher conversion of ethanol and production of hydrogen than ITQ-6 containing Ni (Ni/ITQ-6). The lower size of the metallic cobalt particles shown in Co/ITQ-6 seems to be the major responsible of its higher catalytic performance. Regarding the reaction by-products (CO, CH 4 , C 2 H 4 O and CO 2), Co/ITQ-6 showed the lowest selectivity at medium and high temperatures (773 and 873 K). At low reaction temperatures (673 K) the dehydrogenation reaction predominates in the Co/ITQ-6, what it is supported by the high concentration of acetaldehyde detected at this temperature. In the case of the Ni/ITQ-6 the main side reaction at 673 K seems to be the methanation reaction since large concentrations of methane are detected. Stability studies were also carried out showing lower deactivation of Co/ITQ-6 at large reaction times (24 h). Characterization of the exhausted catalysts after reaction showed the presence of coke in both catalysts. Nevertheless, Co/ITQ-6 presented the lowest coke deposition. In addition, Co/ITQ-6 exhibited the lowest metal sinterization, what could be also account for the lower deactivation exhibited by this sample. This fact could be related to the higher interaction between the cobalt metallic particles and the ITQ-6 support as the H 2 -TPR studies demonstrate. • Ethanol steam reforming catalysts based on Co or Ni supported on ITQ-6 zeolite is prepared by the first time. • Higher ethanol conversion and hydrogen selectivity is exhibited by the catalyst with Co. • The lower size of the metal Co particles is the major responsible of its higher catalytic activity. • Higher stability is exhibited by the Co catalyst (lower coke deposition and sinterization of the metallic particles). [ABSTRACT FROM AUTHOR]