Nickel Species Research Articles

Controlled synthesis and fine-tuned interface of NiS nanoparticles/Bi2WO6 nanosheets heterogeneous as electrocatalyst for oxygen evolution reaction

Heterojunction engineering is one of the commonly used methods for developing electrocatalyst to enhance catalytic activity and stability due to the unique interfacial coupling synergistic. Herein, a strong-coupling 0D/2D NiS/Bi2WO6 heterogeneous electrocatalyst was successfully synthesized through a facile hydrothermal and calcination route. Electrochemistry results revealed that the NiS/Bi2WO6-4 catalyst not only exhibited competitive OER catalytic activity with smaller overpotential (527 mV) and lower Tafel slope (238 mV dec−1) but also delivered long-term stability (at 1.73 V vs. RHE for 13 h). Such excellent properties are mainly due to (1) the substantial active sites are provided by NiS nanoparticles evenly anchored on Bi2WO6 nanosheets, (2) the O-Ni-S bond structure acts as the bridge in heterointerface, which improves the charge and mass transfer rate as well as stabilizes the heterostructure, (3) Most importantly, the bonding of Ni and O changes the valence-bond environment around the nickel species, which is more conducive to balance between the adsorption of OH− and the desorption of O2 in the oxygen evolution reaction. This non-precious NiS/Bi2WO6 heterojunction catalyst is designed with the 0D/2D heterointerface engineering, which may open a new train of thought to design new promising and highly efficient OER electrocatalysts.

Investigation on catalytic hydrodeoxygenation of eugenol blend with light fraction in bio-oil over Ni-based catalysts

In this work, HZSM-5, Al-SBA-15 and Al-SBA-15/HZSM-5 were adopted as supporting materials for the nickel-based catalysts used in hydrodeoxygenation process. Incipient wetness impregnation method was employed to load nickel species onto these materials. The physicochemical characterization was carried out using advanced instruments. The effect of composition of nickel-based catalysts on hydrodeoxygenation (HDO) reaction was studied. Support materials of nickel-based catalyst have a significantly impact on HDO activity. The highest selectivity (67.9%) of propyl-cyclohexane was obtained over nickel based Al-SBA-15/HZSM-5 catalyst, and nearly all the eugenol was completely hydrodeoxygenated after reaction. The impact of light fractions existed in bio-oil on phenols upgrading process was investigated. The conversion of eugenol mixed with light fractions reached nearly 100% for all the reactions. Eugenol mixed with light fractions as reactant could reduce ring break reaction during hydrodeoxygenation process. The selectivity of alkanes remained nearly unchanged after adding ethylene glycol into the reactant. However, the selectivity of propyl-cyclohexane was significantly decreased by mixing furfural or acetic acid with eugenol as reactant.

Modular Synthesis of Diarylalkanes by Nickel-Catalyzed 1,1-Diarylation of Unactivated Terminal Alkenes

A nickel-catalyzed 1,1-diarylation of electronically unbiased alkenes has been developed, providing straightforward access to diarylalkanes from readily available materials. Importantly, both the e...

Impacts of metal loading in Ni/attapulgite on distribution of the alkalinity sites and reaction intermediates in CO2 methanation reaction

Both metal sites and alkaline sites are essential parameters for a catalyst used in methanation of CO2. This study investigated the impacts of the relative abundance of metal sites and alkaline sites on the catalytic performances of nickel-based catalyst with attapulgite, a natural mineral, as the support. The results showed that the increase of nickel loading to attapulgite significantly decreased the abundance of alkaline sites, remarkably enhanced the catalytic activity, and suppressed the formation of CO. The in situ DRIFTS characterization of the CO2 methanation indicated that the alkaline sites favored formation of the oxygen-containing reaction intermediates such as CO∗, –OH, ∗CO2, formate, carbonate and bicarbonate species. In comparison, metallic nickel species promoted their further hydrogenation to form CH4. Besides the absorption/activation of ∗CO2 was more preferable on surface of metallic nickel, but not on the alkaline sites. The availability of the alkaline sites was not as important as the metallic nickel species for preparation of an efficient catalyst for CO2 methanation.

Effect of Support and Chelating Ligand on the Synthesis of Ni Catalysts with High Activity and Stability for CO2 Methanation

Carbon dioxide methanation was carried out over Ni-based catalysts on different supports and chelating ligands in microreactors. To investigate the influence of chelating ligands and supports, the Ni catalysts were prepared using different support such as CeO2, Al2O3, SiO2, and SBA-15 by a citric acid (CA)-assisted impregnation method. The properties of the developed catalysts were studied by X-ray diffraction (XRD), Transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) measurement, and the results show that the addition of CA in the impregnation solution improved the dispersion, refines the particle size, and enhanced the interaction of nickel species. The catalytic performance of the developed Ni catalysts were evaluated by CO2 methanation in microreactors in the temperature range of 275 °C–375 °C under 12.5 bar pressure. All the catalysts exhibit high CO2 conversion and extremely high selectivity to methane. However, the catalysts prepared via CA-assisted method exhibited excellent activity and stability, compared with Ni catalysts prepared by a conventional impregnation method, which could be attributed to highly dispersed nickel particles with strong metal–support interaction. The activity of CO2 methanation followed the order of Ni/CeO2-CA > Ni/SBA-15-CA > Ni/Al2O3-CA > Ni/SiO2-CA > Ni/CeO2. The Ni/CeO2 catalysts have also been prepared using different chelating ligands such as ethylene glycol (EG), sucrose (S), oxalic acid (OA) and ethylene diamine tetra acidic acid (EDTA). Among the tested catalysts prepared with different support and chelating ligands, the Ni/CeO2 catalyst prepared via CA-assisted method gave superior catalytic performance and it could attain 98.6% of CO2 conversion and 99.7% methane selectivity at 325 °C. The partial reduction of the CeO2 support generates more surface oxygen vacancies and results in a high CO2 conversion and methane selectivity compared with other catalysts. The addition of CA as promoter favored the synergistic effect of Ni and support, which led to high dispersion, controls the size, and stabilizes the Ni nanoparticles. Furthermore, the Ni/CeO2-CA catalyst yields high CO2 conversion in a time-on-stream study due to the ability of preventing the carbon deposition and sintering of Ni particles under the applied reaction conditions. However, the Ni/Al2O3-CA and Ni/SBA-15-CA catalysts showed stable performance for 100 h of time on stream.

Tailoring the surface properties of Ni/SiO2 catalyst with sulfuric acid for enhancing the catalytic efficiency for steam reforming of guaiacol

The impregnation of sulfuric acid aqueous solution to silica is a traditional method to prepare the solid acid catalyst (SO42−/SiO2) via bonding of the SO42− with surface atoms of silica to generate Brønsted acidic sites and Lewis acidic sites. The results in this study indicated the introduction of sulfuric acid could also impact the interaction between silica and subsequently loaded nickel species. The impregnation of sulfuric acid (i.e. 0.5 M) to Ni/SiO2 catalyst could enhance the dispersion of nickel via reducing nickel particle size, suppress sintering of nickel and increase abundance of the acidic sites with strong strength, which significantly enhanced the catalytic activity, stability and resistivity towards coking in steam reforming of guaiacol. The acidic sites with the strong strength aided the cracking of guaiacol to facilitate the subsequent reforming over metallic nickel sites. After impregnation of appropriate amount of sulfuric acid (i.e. 0.1 M or 0.5 M), the coke formed in amorphous form with low thermal stability was transformed into the coke in form of carbon nanotube with high thermal stability. The former type of coke induced rapid deactivation of the catalyst, while the latter type of coke did not.

On the effect of yttrium promotion on Ni-layered double hydroxides-derived catalysts for hydrogenation of CO2 to methane

Ni-containing mixed oxides derived from layered double hydroxides with various amounts of yttrium were synthesized by a co-precipitation method at constant pH and then obtained by thermal decomposition. The characterization techniques of XRD, elemental analysis, low-temperature N2 sorption, H2-TPR, CO2-TPD, TGA and TPO were used on the studied catalysts. The catalytic activity of the catalysts was evaluated in the CO2 methanation reaction performed at atmospheric pressure. The obtained results confirmed the formation of nano-sized mixed oxides after the thermal decomposition of hydrotalcites. The introduction of yttrium to Ni/Mg/Al layered double hydroxides led to a stronger interaction between nickel species and the matrix support and decreased nickel particle size as compared to the yttrium-free catalyst. The modification with Y (0.4 and 2 wt%) had a positive effect on the catalytic performance in the moderate temperature region (250–300 °C), with CO2 conversion increasing from 16% for MO-0Y to 81% and 40% for MO-0.4Y and MO-2.0Y at 250 °C, respectively. The improved activity may be correlated with the increase of percentage of medium-strength basic sites, the stronger metal-support interaction, as well as decreased crystallite size of metallic nickel. High selectivity towards methane of 99% formation at 250 °C was registered for all the catalysts.

Level and speciation of nickel in some forages in relation to spatial and temporal fluctuations.

The present experimental work was conducted at different sites of district Bhakkar, a semiarid region of Pakistan, to assess whether the goats are suffering nickel deficiency or toxicity and what are the possible seasonal effects on the availability and translocation of nickel in food chain. A total of 27 forage and 320 goats according to four physiological stages [does (she goat), bucks (he goat), wether (castrated), juvenile (6month)] were recruited for this study. To fulfill this objective, soil, forage, blood plasma, urine, and feces samples were collected in 4 seasons of the year at 2 sites and were analyzed by atomic absorption spectrophotometer for nickel concentration. Different indices BCF, EF, and PLI were also studied to check the metal transfer. The results showed that sites had significant (P < 0.05) effect on nickel concentration in soil, forage, and goats. On the other hand, season and site x season had nonsignificant (P > 0.05) effects on nickel level in soil and goats. The soil (0.68-0.71mgkg-1), forage (3.41-3.70mg/kg), and blood (0.21-0.28mg/l) level was lower than the permissible limits, while feces (0.57-1.34mg/kg) and urine (0.35-1.32mg/l) had enough concentration of nickel. Sources showed significant (P < 0.05) effects on Ni level in all stages of goats. All stages of goats except Wether (castrated) showed low level of nickel in blood. Most fluctuations in nickel concentration were observed in (S1) summer (low) and spring (S4) (high) season as a whole, while overall site 2 had high level of nickel than site 1. Thus, nickel showed deficiency in soil, forage, as well as in all stages of goats except wether goats. Nickel containing mineral mixtures are essential for does (she goat), bucks (he goat), and juveniles (6months old), so application of Ni containing fertilizers to the soil and forage of that region and supplementation of Ni mineral mixture for grazing ruminants should be done.

Effects of Ni–Al2O3 interaction on NiMo/Al2O3 hydrodesulfurization catalysts

A series of NiMo/γ-Al2O3 hydrodesulfurization (HDS) catalysts with different metal–support interactions were first prepared by a conventional impregnation method through changing the calcination temperature. The physicochemical properties of nickel species and molybdenum species in the oxidic and sulfidic catalysts were characterized by X-ray fluorescence spectroscopy, X-ray diffraction, N2 adsorption–desorption, ultraviolet–visible spectroscopy, Raman spectroscopy, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. It was found both the interaction between nickel and γ-alumina (Ni–Al2O3 interaction) and the interaction between molybdenum and γ-alumina (Mo–Al2O3 interaction) gradually increase with increasing calcination temperature. However, the calcination temperature has a weak influence in the sulfidation degree of molybdenum species but a huge effect on the decoration degree of Ni species on edges of MoS2 nanoslabs. The decoration degree of Ni species visibly declines with increasing calcination temperature, but the sulfidation degree of molybdenum stays nearly parallel at the same time, indicating that Ni rather than Mo is more sensitive to the calcination temperature. In addition, the MoS2 morphology could be impacted by the availability of surface nickel atoms. These results suggest that the Ni–Al2O3 interaction imposes a more dominant influence on the HDS catalysts. Then the HDS performance was evaluated using dibenzothiophene as the model reactant, and through correlating the catalyst structures with the activity, an original suggestion about the effects of the Ni–-Al2O3 interaction on HDS performance was given: the Ni–Al2O3 interaction not only enhances the availability of surface nickel atoms to form more Ni–Mo–S active sites, but also improves the microstructures of MoS2, i.e., shorter nanoslabs and higher stacking layers, which together enhance the apparent activity and intrinsic activity of Ni–Mo catalysts. The present work reveals that finely adjusting Ni–Al2O3 interaction is an effective strategy for improving the performance of hydrodesulfurization catalysts.

3d-d Excited States of Ni(II) Complexes Relevant to Photoredox Catalysis: Spectroscopic Identification and Mechanistic Implications.

Synthetic organic chemistry has seen major advances due to the merger of nickel and photoredox catalysis. A growing number of Ni-photoredox reactions are proposed to involve generation of excited nickel species, sometimes even in the absence of a photoredox catalyst. To gain insights about these excited states, two of our groups previously studied the photophysics of Ni(t-Bubpy)(o-Tol)Cl, which is representative of proposed intermediates in many Ni-photoredox reactions. This complex was found to have a long-lived excited state (τ = 4 ns), which was computationally assigned as a metal-to-ligand charge transfer (MLCT) state with an energy of 1.6 eV (38 kcal/mol). This work evaluates the computational assignment experimentally using a series of related complexes. Ultrafast UV-Vis and mid-IR transient absorption data suggest that a MLCT state is generated initially upon excitation but decays to a long-lived state that is 3d-d rather than 3MLCT in character. Dynamic cis,trans-isomerization of the square planar complexes was observed in the dark using 1H NMR techniques, supporting that this 3d-d state is tetrahedral and accessible at ambient temperature. Through a combination of transient absorption and NMR studies, the 3d-d state was determined to lie ∼0.5 eV (12 kcal/mol) above the ground state. Because the 3d-d state features a weak Ni-aryl bond, the excited Ni(II) complexes can undergo Ni homolysis to generate aryl radicals and Ni(I), both of which are supported experimentally. Thus, photoinduced Ni-aryl homolysis offers a novel mechanism of initiating catalysis by Ni(I).

Recent Advances in Nickel-Catalyzed Three-Component Difunctionalization of Unactivated Alkenes

Catalytic, intermolecular difunctionalization of alkenes represents an efficient and diverse protocol for the buildup of molecular complexity from abundant materials by forging two chemical bonds in a single operation. Despite important progress in this area, transition-metal-catalyzed three-component difunctionalization of unactivated alkenes remains underdeveloped, mainly because of the low reactivity, reduced polarization, and high tendency toward β-hydride elimination of these compounds. In this context, nickel-catalyzed, selective, intermolecular difunctionalization methods that generally proceed via two distinct reaction pathways, migratory insertion of nickel species into alkenes and radical addition to alkenes, have been developed. This short review highlights recent advances in this area.1 Introduction2 Nickel-Catalyzed Three-Component Difunctionalization of Unactivated­ Alkenes via Migratory Insertion Processes3 Nickel-Catalyzed Three-Component Difunctionalization of Unactivated­ Alkenes via Radical Processes4 Conclusions and Perspectives

Ni supported on the CaO modified attapulgite as catalysts for hydrogen production from glycerol steam reforming

The Ni catalyst supported on CaO-modified attapulgite (CaO-ATP) were synthesized by wet impregnation method at a constant Ni metal loading (10 wt%). The catalyst was tested by carrying out a glycerin steam reforming reaction under the following conditions: 400–800 °C, W/G is 3, GHSV is 1 h−1. Ni–CaO-ATP exhibited the highest hydrogen yield (85.30%) and glycerol conversion (93.71%) at 600 °C. The catalysts were characterized by N2 adsorption/desorption, BET, XRD, H2-TPR, TG and SEM. The results show that ATP has good resistance to carbon deposition. As an attapulgite modifier of Ni–CaO-ATP, CaO promotes the dispersion of the active component nickel species, which would promote the water gas shift reaction, leading to the improving of hydrogen yield. In addition, the addition of Ca would further enhance the inhibition of carbon deposition and prolong the life of the Ni–CaO-ATP catalyst.

The effect of oxidation state of metal on electrochemical and photochemical driven hydrogen evolution catalyzed by nickel complexes of maleonitriledithiolate ligands

Two nickel-based catalysts, TBA2[NiII(mnt)2] 1 and TBA[NiIII(mnt)2] 2 are formed by the reactions of NiCl2·6H2O, Na2(mnt), and tetra-n-butylammoniumbromide (TBABr) without or with iodine (I2) (mnt = 2,2-dicyanoethylene-1,1-dithiolate), respectively. Under an overpotential (OP) of 941.6 mV, complexes 1 and 2 can electrocatalyze hydrogen evolution from acetic acid with a turnover frequency (TOF) of 36.3 and 148.31 mol H2/mol catalyst/h, respectively. Under blue light (λ max = 469 nm), 1 or 2, together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H2A) as a sacrificial electron donor, can produce hydrogen with a turnover number (TON) of 7760 and 17,570 moles of H2 per mole of catalyst during 35 h irradiation, respectively. The average value of apparent quantum yield (AQY) is ∼9.2% (complex 1) and 28% (complex 2), respectively. The results indicate that the nickel(III) complex has a better active activity for hydrogen production than the nickel(II) species.

Understanding the removal of V, Ni and S in crude oil atmospheric residue hydrodemetallization and hydrodesulfurization

This study describes the use of gel permeation chromatography inductively coupled plasma high-resolution mass spectrometry (GPC ICP HRMS) to examine and explain two important petroleum industry catalytic processes: hydrodemetallization (HDM) and hydrodesulfurization (HDS).The sulfur, nickel and vanadium species size distributions in atmospheric residue fractions were studied to track their evolution during both catalytic processes and examine their mechanisms, especially those mechanisms linked to changes in temperature and initial deactivation via coke laydown. Chromatogram shapes as well as peak areas were used to study the V, Ni and S aggregate types and concentrations in the feedstock as well as in the product after varying the operating temperature and residence time at a constant temperature. For the V and Ni compounds, the low and medium molecular weight (LMW and MMW, respectively) aggregates are easily hydrotreated under all conditions, while the high molecular weight (HMW) compounds are more refractory. For the S compounds, a different reactivity pattern was observed whereby the LMW, MMW and HMW aggregates were more similar in their reactivity, showing that the catalyst is less selective towards a certain aggregate size for the S compounds compared to the V or Ni compounds.

Influence of the Cathode Potential on Electrode Interactions within a Li4Ti5O12 vs LiNi3/5Mn1/5Co1/5O2 Li-Ion Battery

Interactions occurring between positive and negative electrodes and their impact on electrode–electrolyte interfaces during constant current cycling in LiNi3/5Mn1/5Co1/5O2//Li4Ti5O12 li-ion batteries are investigated at various upper cutoff voltages by performing XPS and ToF-SIMS analysis. Below 4.3 V (potential of NMC electrode vs Li0/Li+), good capacity retention and low impedance increase over cycles are obtained whereas at higher cycling positive electrode potential, serious capacity loss and critical increase of electrochemical impedance are observed due to electrolyte degradation at the Ni-rich NMC electrodes. This study highlights that salt (LiF and fluorophosphates) and solvents (–CO containing species) degradation products and NMC dissolution products such as manganese or nickel species are formed at the NMC electrodes then migrate to the LTO electrodes surface in full-cells, and these phenomena are intensified at high voltage. Moreover, the formation and the deposition of organo-fluoro-phosphates in the outer part of the SEI of LTO electrodes is revealed thanks to ToF-SIMS molecular in-depth analysis. These results provide valuable insights on the behavior of interfaces at LTO electrodes upon cycling vs NMC at high potential. Overall, failure mechanisms are driven by oxidative parasitic reactions at the cathode and interactions with the anode.

A recyclable heterogeneous-homogeneous-heterogeneous NiO/AlOOH catalysis system for hydrocarboxylation of acetylene to acrylic acid.

Concerns about the high-valued utilization of coal- and natural gas-based acetylene has provided particular impetus for exploration of acrylic acid (AA) production via one-step hydrocarboxylation reaction. Motivated by simple recovery, recycling and reuse of the catalyst, we report a high-performance NiO/AlOOH catalyst with AA space-time-yield of 412 gAA gcat.−1 h−1, obtainable by a simple incipient wetness impregnation method. Detailed kinetic and controlled experiments confirmed that nickel species on such a solid catalyst provide a heterogeneous–homogeneous–heterogeneous catalytic cycle where the chelates formed between CO and leached nickel act as the active species. The thorough recovery of leached nickel species improves the catalyst stability greatly. These preliminary findings indicate further prospects for new heterogeneous catalyst design in traditional homogeneous catalytic systems.

Ni nanocatalysts supported on mesoporous Al2O3-CeO2 for CO2 methanation at low temperature.

The selectivity and activity of a nickel catalyst for the hydrogenation of carbon dioxide to form methane at low temperatures could be enhanced by mesoporous Al2O3–CeO2 synthesized through a one-pot sol–gel method. The performances of the as-prepared Ni/Al2O3–CeO2 catalysts exceeded those of their single Al2O3 counterpart giving a conversion of 78% carbon dioxide with 100% selectivity for methane during 100 h testing, without any deactivation, at the low temperature of 320 °C. The influence of CeO2 doping on the structure of the catalysts, the interactions between the mesoporous support and nickel species, and the reduction behaviors of Ni2+ ions were investigated in detail. In this work, the addition of CeO2 to the composites increased the oxygen vacancies and active metallic nickel sites, and also decreased the size of the nickel particles, thus improving the low temperature catalytic activity and selectivity significantly.

Flexible cycloalkyl substituents in insertion polymerization with α-diimine nickel and palladium species

The investigation of the relationship between the structure of the catalyst and the microstructure of the obtained polymer has attracted much attention and broad interest in the field of transition metal-catalyzed olefin polymerization.

A remote nonconjugated electron effect in insertion polymerization with α-diimine nickel and palladium species

The remote nonconjugated electronic perturbations exert great influence on ethylene polymerization.

Ni-Based heterogeneous catalysts for the transformation of fatty acids into higher yields of O-free hydrocarbons

Chelation of nickel species was used for the synthesis of highly active, stable and selective heterogeneous catalysts for biomass conversion.