Metallic Nickel Phase Research Articles

Structural, morphological, and magnetic properties of NiF2 assisted growth of Ni-multi walled carbon nanotubes

This paper reports the synthesis and magnetic properties of NiF2 assisted growth of multi-walled carbon nanotubes. Ni-Multi-Walled Carbon Nanotubes (Ni-MWCNT) were synthesized by catalytic decomposition of Xylene (C8H10) and NiF2 (as a precursor for metallic Ni) using Chemical Vapor Deposition (CVD). The presence of graphitic carbon crystallization and a dominant metallic nickel phase is confirmed by XRD and Raman analysis. The in-situ formation of Ni nanoparticles from NiF2 precursor successfully aids the growth of Ni-MWCNTs. The diameter of synthesized Ni-MWCNT was measured to be around 100 nm. Ni-MWCNT exhibit a weak ferromagnetic property due to the presence of metallic Ni residues.

An Earth‐Abundant Ni‐Based Single‐Atom Catalyst for Selective Photodegradation of Pollutants

Highly efficient catalytic technologies are urgently needed to remove pharmaceutical pollutants from water. In this work, the preparation, characterization, and photocatalytic performance of an earth‐abundant Ni‐based heterogeneous catalyst featuring highly dispersed Ni species over nanosheets of carbon nitride are reported. The absence of any metallic nickel phase has been confirmed by spectrometric analyses, unveiling the NiN environment for the metal centers and attaining synergistic interfacial carrier transfer via NNiN coordination. By combining advanced characterizations with kinetic investigations, it is demonstrated that these newly formed isolated single atoms of Ni act as a bridge, facilitating faster electron transfer, increasing the charge density on Ni, and reducing the photocarrier transfer barrier. Compared to literature precedents, this substantially enhances the degradation of gemfibrozil, a model pharmaceutical pollutant found in wastewater, reducing the formation of toxic benzenic byproducts during photooxidation. This effect, which is not observed over conventional nanoparticle‐based materials, discriminates the role of single‐atom and nanoparticle‐based catalysis during degradation of pollutants. This work opens new avenues in designing selective and earth‐abundant photocatalysts for advanced oxidation processes, showing the importance of atom coordination to control the surface and catalytic properties of single‐atom materials.

Performance of Carbon-Nickel Composite Coatings on Laser Surface Roughened Aluminum Foils for Supercapacitor Current Collectors

Surface-engineered aluminum current collectors were developed through laser-based surface modification methods. Their performances as current collectors in supercapacitors clearly outperformed state-of-the-art carbon-coated commercial foils and were close to ideal gold foils, thanks to the enhanced interfaces provided by their engineered surfaces. Surface modifications included roughening by laser ablation in high vacuum, and coating with a carbon-nickel (C0.97Ni0.03) composite thin film deposited using pulsed laser deposition. The main improvement was obtained after coating the aluminum foil with the carbon-nickel protective layer, which was attributed to the almost pure sp2 bonding state of the carbon and a mostly metallic nickel phase. The surface roughening treatment further decreased the interface resistance by providing a higher contact surface and a better mechanical anchorage of the active materials layer. The combination of laser roughening in vacuum conditions and subsequent deposition of an electronically conductive protective coating was therefore demonstrated as an efficient approach to improve the performance of current collectors for supercapacitors.

Availability of steam impacts coke properties in steam reforming of acetic acid

Steam to carbon ratio (S/C) determines the availability of oxygen-containing species during steam reforming, which not only affect the amount of coke formed, but also might impact physicochemical properties of the coke generated. In this study, the effect of S/C on the coke formation in steam reforming of acetic acid was assessed. The results indicated that dissociative absorption of acetic acid generated the intermediates containing both CO and CC groups even at 100 °C. At low S/C, the insufficient ∗OH reacted with carbonaceous intermediates such as CHx to form more carbonyl species, leading to significant coking and lower gas yields. Sufficient ∗OH at high S/C facilitated transformation of the carbonyl-containing species into gases, minimizing coking. The varied amount of coke showed significant effect on the diffraction of metallic nickel phase, the particle size of Ni and the absorption for the Si–O–Si functional groups on spent catalysts. The coke formed at low S/C was more aromatic with high thermal stabilities, while the coke formed at high S/C was more aliphatic with low thermal stabilities. The involvement ∗OH species in coking process determined not only properties but also morphologies of the coke. The coke formed at low S/C showed bamboo-like, dendritic or twisted rope-like structure. While the higher S/C favored the generation of the carbon nanotubes with smooth outer surface.

Molybdenum and Nickel Nanoparticles Synthesis by Laser Ablation towards the Preparation of a Hydrodesulfurization Catalyst

A clean straightforward laser ablation method in deionized (DI) water is reported for the synthesis of Molybdenum (Mo) and Nickel (Ni) nanoparticles (NPs). The structural, morphological, and optical properties of the as-synthesized nanoparticles were investigated. Particle size was estimated to be less than 10 nm, the UV–vis spectra of the samples show the formation of H2MoO4 and NiO. The XRD results for the Ni sample show the presence of two phases, cubic nickel oxide, and an fcc metallic nickel phase, indicating the possible formation of Ni/NiO compound. The nanoparticles synthesized were used as precursors in the production of a NiMo/γ-Al2O3 catalyst. The textural and structural properties, chemical composition, and catalytic performance in a hydrodesulfurization (HDS) reaction are reported. The textural and structural properties results show the lack of pore-blocking due to the small sizes and the distribution of the metallic nanoparticles on the support. Chemical composition measured by XPS shows a ratio Ni/Mo of 1.34. Therefore, possibly Ni was deposited on Mo covering part of its active area, occupying active sites of Mo, removing its effective surface and resulting in a relatively low conversion of DBT (17%). A lower Ni/Mo ratio is required to improve the model system, which could be achieved by changing parameters at the production of the nanoparticles. The model system can also be further tuned by changing the size of the nanoparticles.

Ethylene glycol dry reforming on Ni/Al2O3 catalyst for syngas generation

It is the first time ethylene glycol dry reforming (EGDR) reaction was carried out for syngas production on 10%Ni/Al2O3 catalyst in a tubular fixed-bed reactor at atmospheric condition. Wet-impregnation method was employed for the synthesis of 10%Ni/Al2O3 catalyst. The results of X-ray diffraction measurement revealed the presence of γ-Al2O3, NiO, NiAl2O4, Ni0 and graphitic carbon phases on the surface of spent 10%Ni/Al2O3 catalyst. H2 temperature-programmed reduction indicates that NiO and NiAl2O4 phases were totally reduced to metallic nickel phase at reduction temperature above 970 K. EGDR activity appeared to be steady with time-on-stream beyond 5-7 h. Catalytic activity was considerably improved with increasing feed ratio of CO2:C2H6O2 from 1:1 to 2.5:1.

Controllable synthesis of metallo-alkoxide precursor-derived nickel aluminate spinels using TEA-gel process and morphology-dependent reducibility

A study was made of the different preparation methods affecting the morphology and reducibility of the obtained NiAl2O4 spinels. The NiAl2O4 with various morphologies has been fabricated through the dependent control of TEA (triethanolamine) -gel parameters. Compared to the NiAl2O4 prepared from a direct calcination of spinel precursors, the superb structural characteristics of the NiAl2O4 including large surface area and well-defined interconnected nanoparticles were observed via the TEA-gel route. The NiAl2O4 prepared by TEA-gel method yields the highest degree of surface reduction with the largest amount of metallic nickel phase found in the spinels. This spinel also had the lowest initial temperature of reduction. The results indicate that the NiAl2O4 prepared by the TEA−gel technique using our new spinel alkoxide precursor has a promising prospect in the preparation of nickel catalyst supports where there is a need to avoid the traditional multiple procedures that are time-, solvent-as well as high energy-consuming.

Electrospinning synthesis of 3D porous NiO nanorods as anode material for lithium-ion batteries

AbstractThree-dimensional NiO nanorods were synthesized as anode material by electrospinning method. X-ray diffraction results revealed that the product sintered at 400 °C had impure metallic nickel phase which, however, became pure NiO phase as the sintering temperature rose. Nevertheless, the nanorods sintered at 400, 500 and 600 °C had similar diameters (∼200 nm).The NiO nanorod material sintered at 500 °C was chip-shaped with a diameter of 200 nm and it exhibited a porous 3D structure. The nanorod sintered at 500 °C had the optimal electrochemical performance. Its discharge specific capacity was 1127 mAh·g−1initially and remained as high as 400 mAh·g−1at a current density of 55 mA·g−1after 50 cycles.

Photoemission electron microscopy of arrays of submicron nickel rods in a silicon dioxide matrix

Arrays of Ni rods (∼500 nm diameter) formed by the ion-track technology in combination with electrochemical deposition into a SiO2 matrix on the surface of single-crystal silicon plates have been investigated using photoemission electron microscopy with high-intensity synchrotron (undulator) radiation. An analysis of the Ni L 2,3 X-ray absorption near-edge structure (XANES) spectra has demonstrated that rod-like structures in pores and connecting bridges between the rods are formed by a metallic nickel phase, which is stable to oxidation by atmospheric oxygen. No formation of intermediate compound phases (nickel silicides and oxides) is observed at the Ni/SiO2 heterojunction, whereas oxidized nickel(II) species are identified on the surface of the SiO2 matrix, which presumably can be attributed to nickel silicate and hydroxide compounds formed upon nickel(II) chemisorption in electrochemical deposition electrolytes.

Synthesis and Characterization of Nickel Nanoparticles Prepared Using the Aquolif Approach

We report on the synthesis of nickel nanoparticles using a combination of chemical reduction and freezing-drying processes that we named the aquolif approach. The X-ray diffraction (XRD) patterns reveal that the synthesized nanoparticles were composed of a single metallic nickel phase. The average crystallite sizes of the nickel nanoparticles were determined using the Scherrer method. The average crystallite sizes increased from 8±3 to 16±3 nm as the annealing temperature increased, which is consistent with the XRD and transmission electron microscopy results. The zero-field-cooling and field-cooling (ZFC-FC) magnetization curves reveal that the nickel nanoparticles exhibited superparamagnetic behavior with a high blocking temperature and a surface effect at lower temperatures. Our experimental results demonstrate that the aquolif approach can be successfully scaled up to industrially prepare other types of metallic nanoparticles.

Pure face-centered-cubic (fcc) and hexagonal-close-packed (hcp) nickel phases obtained in air atmosphere sol–gel process and fcc nickel phase obtained in N2 protected sol–gel process

Air atmosphere sol–gel process is often applied to prepare metallic oxide materials. Here we show that metallic nickel phase can also be obtained by citric acid (CA) based air atmosphere sol–gel process in appropriate procedure. Pure fcc or hcp phases of nickel can be obtained in air atmosphere by using CA, nickel (II) acetylacetone, organic solvents and organic surfactants such as oleylamine (OAM), hexadecylamine. However, only NiO can be prepared by aqueous CA based sol–gel process. Oleic acid and OAM can also be used in organic solution mediated sol–gel process to prepare nickel nanoparticles in N2 atmosphere with pure fcc phase at appropriate calcination temperature when 1-hexyl alcohol has been used as solvent. Impurities, such as hcp Ni or Ni3N phase, do not occur in this experimental condition. Our results provide a new and facile way in preparation of metallic nanoparticles.

Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

Ni/SiO2 materials with identical composition (SiO2/Ni = 1.0) have been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO2 precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H2-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni2+-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni2+-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430°C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of high activity in the vegetable oil hydrogenation.

Development of a Ni–Ce0.8Zr0.2O2 catalyst for solid oxide fuel cells operating on ethanol through internal reforming

Inexpensive 20wt.% Ni–Ce0.8Zr0.2O2 catalysts are synthesized by a glycine nitrate process (GNP) and an impregnation process (IMP). The catalytic activity for ethanol steam reforming (ESR) at 400–650°C, catalytic stability and carbon deposition properties are investigated. Ni–Ce0.8Zr0.2O2 (GNP) shows a higher catalytic performance than Ni–Ce0.8Zr0.2O2 (IMP), especially at lower temperatures. It also presents a better coking resistance and a lower graphitization degree of the deposited carbon. The superior catalytic activity and coke resistance of Ni–Ce0.8Zr0.2O2 (GNP) is attributed to the small particle size of the active metallic nickel phase and the strong interaction between the nickel and the Ce0.8Zr0.2O2 support, as evidenced by the XRD and H2-TPR. The Ni–Ce0.8Zr0.2O2 (GNP) is further applied as an anode functional layer in solid oxide fuel cells operating on ethanol steam. The cell yields a peak power density of 536mWcm−2 at 700°C when operating on EtOH–H2O gas mixtures, which is only slightly lower than that of hydrogen fuel, whereas the cell without the functional layer failed for short-term operations. Ni–Ce0.8Zr0.2O2 (GNP) is promising as an active and highly coking-resistant catalyst layer for solid-oxide fuel cells operating on ethanol steam fuel.

MCM-41 supported PdNi catalysts for dry reforming of methane

A series of bimetallic PdNi catalysts supported on mesoporous MCM-41 with different Ni content (Ni/Si ratio of 0.2–0.4) was synthesized. The effect of Pd addition to Ni-containing catalysts as well as the effect of the Ni content on the surface and catalytic properties of the catalysts was studied. The samples were characterized using various techniques, such as energy-dispersive X-ray spectroscopy, N2 adsorption–desorption isotherms, X-ray diffraction, thermogravimetric and differential analyses, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and temperature-programmed reduction. Reforming of methane with carbon dioxide was used as a test reaction. The results indicated that the addition of a small amount of Pd (0.5%) to Ni-containing catalysts leads to formation of small nano-sized, easy reducible NiO particles. Agglomeration of NiO as well as of metallic nickel phase over PdNi samples increased with increasing the Ni content. Formation of filamentous carbon over surface of spent monometallic Ni and bimetallic PdNi catalyst was observed. In spite of filamentous carbon deposition, the catalytic activity and stability of bimetallic PdNi catalysts are higher than those of monometallic Ni one. Within bimetallic system, the PdNi catalyst with Ni/Si ratio of 0.3 revealed the best performance and stability caused by presence of small nickel particles well dispersed on the catalyst surface.

Influence of the oxygen pretreatment on the CO 2 reforming of methane on Ni/β-SiC catalyst

The influence of the O 2 pretreatment on the CO 2 reforming of methane to synthesis gas has been investigated with Ni catalysts supported on β-SiC extrudate. The structure and properties of the catalysts were characterised by SEM, TEM and XRD techniques. The pretreatment of the catalyst by a mixture of CO 2 and O 2 significantly improves the catalytic activity for the CO 2 reforming. On the Ni 5 wt.% supported on β-SiC catalyst, the CH 4 conversion has reached 90% with the O 2 pretreatment instead of 80% by direct activation under CO 2/CH 4 mixture. The oxygen pretreatment seems to stabilize the metallic nickel phase instead of NiSi 2.

HARD AND TOUGH NANOCOMPOSITE TiN-Ni COATINGS DEPOSITED BY REACTIVE ION BEAM ASSISTED DEPOSITION

A new category of hard nanocomposite coatings with adjustable improved hardness or enhanced toughness consisting of nanocrystalline (nc-) titanium nitride grains embedded in an amorphous (a-) metallic intergranular nickel phase i.e. nc - TiN / a - Ni type has been produced and investigated. Coatings were deposited at 573K on different substrates using a reactive dual ion beam sputtering (RDIBS) technique. A composite Ti - Ni target was sputtered with 1.2 keV Ar + ions and the growing films were bombarded with a mixture of 50 eV Ar ++ N 2++ N + ions. XRD, nanoindentation, high load indentation and pin-on-disk tests were used to characterize structural and mechanical properties. By adjusting Ni content enhanced hardness or toughness is obtained with an important improvement in wear resistance corresponding to the coatings exhibiting the highest toughness than highest hardness.

Beneficial effects of the use of a nickel membrane reactor for the dry reforming of methane: Comparison with thermodynamic predictions

The development of a nickel composite membrane with acceptable hydrogen permselectivity at high temperature in a membrane reactor for the highly endothermic dry reforming of methane reaction was the purpose of this work. A thin, catalytically inactive nickel layer, deposited by electroless plating on asymmetric porous alumina, behaved simply as a selective hydrogen extractor, shifting the equilibrium in the direction of a higher hydrogen production and methane conversion. The main advantage of such a nickel/ceramic membrane reactor is the elimination or limitation of the side reverse water gas shift reaction. For a Ni/Al 2O 3 catalyst, containing free Ni particles, normally sensitive to coking, the use of the membrane reactor allowed an important reduction of carbon deposition (nanotubes) due to restriction of the Boudouard reaction. For a Ni–Co/Al 2O 3 catalyst, where the metallic nickel phase was stabilized by the alumina, the selective removal of the hydrogen significantly enhanced both methane conversion (+67% at 450 °C, +22% at 500 °C and +18% at 550 °C) and hydrogen production (+42% at 450 °C, +32% at 500 °C and +22% at 550 °C) compared to the results obtained for a packed-bed reactor. The hydrogen selectivity during the catalytic tests at 550 °C, maintained with constant separation factors (7 for H 2/CH 4, 8 for H 2/CO and 10 for H 2/CO 2), higher than Knudsen values, attested to the high thermal stability of the nickel composite membrane.

A Novel Reduction Method for Ni/γ-Al2O3 Catalyst by a High Frequency Cold Plasma Jet at Atmospheric Pressure

Abstract The Ni/γ-Al2O3 catalyst was reduced by a high frequency cold plasma jet at atmospheric pressure. The performance of the catalyst for carbon dioxide reforming of methane was investigated. The process of catalyst reduction with plasma was quick and simple and was completed in only 10 min, giving activity and selectivity higher than those of the catalyst prepared by the conventional method. At the CH4/CO2 molar ratio of 4/6 and the reaction temperature of 850°C, the methane conversion and CO2 conversion reached up to 95.77% and 75.65%, respectively, and a hydrogen selectivity of 100% and a CO selectivity of 94.79% were obtained over the novel catalyst reduced by plasma. The novel catalyst exhibited good stability during a reaction test for 36 h. XRD characterization showed that only a metallic nickel phase and γ-alumina existed in the catalyst reduced by plasma, and the NiAl2O4 phase and other nickel oxides were not detected. The nickel particle size of the catalyst was smaller than that of the conventional catalyst. An enhanced dispersion was achieved with the plasma reduction.

Effect of accelerators and stabilizers on the formation and characteristics of electroless Ni–P deposits

The effect of thiourea, succinic acid and lead acetate on the formation and characteristics of electroless Ni–P deposits obtained from an acidic hypophosphite reduced electroless nickel bath is addressed in this paper. The rate of deposition of electroless Ni–P coating is found to be a function of concentration of these additives. Thiourea accelerates the rate of deposition up to 0.8 ppm and started to inhibit at a concentration of 1 ppm. Similarly, succinic acid increases the plating rate up to 12 g l −1 and exhibit an inhibiting effect at higher concentrations of the order of 15 g l −1. Addition of lead acetate inhibits the rate of deposition even at a concentration of 0.5 ppm and the extent of inhibition is increased when the concentration is higher than 1 ppm. Addition of these additives also caused a change in phosphorus content of the deposits; lead acetate (1 ppm) tends to increase the phosphorus content whereas thiourea (0.8 ppm) and succinic acid (12 g l −1) tends to decrease the phosphorus content. The X-ray diffraction patterns of electroless Ni–P coatings obtained in the absence of additives and in presence of 1 ppm of lead acetate exhibit a single broad peak centered at 44.5° 2 θ, indicating the amorphous nature of these coatings. The peak broadening suggests a greater tendency to form amorphous structure when lead acetate is used as the additive. In contrast, for electroless Ni–P coatings obtained from thiourea and succinic acid containing baths, besides the reflection from Ni (1 1 1) plane, a weak reflection from Ni (2 0 0) plane is also observed. The X-ray diffraction patterns of electroless Ni–P coatings after annealing at 400 °C for 1 h exhibit the formation of fcc nickel and bct nickel phosphide (Ni 3P) phases in all the cases with Ni 3P (2 3 1) as the most intense reflection. Electroless Ni–P coatings obtained in presence of thiourea and succinic acid exhibit a nodular feature with a typical cauliflower like structure. The size of the nodules is relatively less in the latter case. In contrast, the electroless Ni–P coating obtained in the absence of additives and in presence of 1 ppm of lead acetate is relatively smooth. However, the deposit obtained in the absence of additives reveals the presence of fine particulates, attributed to the precipitation of Ni 3P phases in the absence of stabilizers. The DSC traces of electroless Ni–P coatings exhibit a single well-defined exothermic peak in the temperature range studied in all the cases, which could be attributed to the precipitation of metallic nickel phase and formation of nickel phosphide (Ni 3P) phase. The variation in the peak temperature and the energy evolved during the phase transition is due to the slight variation in the phosphorus content caused by the addition of thiourea, succinic acid and lead acetate. The study recommends that the choice of accelerators and stabilizers should be made only after a careful study.

Preparation and Characterization of Several High-Area NiAl2O4Spinels. Study of Their Reducibility

A rigorous study was made of the different experimental conditions that affect the obtention of high-area spinels. Some of the key factors in the preparation of NiAl2O4, such as precipitation and calcination temperatures, have been carefully studied and correlated to the reducibility of the final spinel. All the samples were characterized by X-ray diffraction, nitrogen physisorption, scanning electron microscopy, temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) techniques. Spinels were obtained with high area (110−220 m2/g) compared with those usually reported. XPS showed that these spinels can be surface reduced. The largest amount of metallic nickel phase was found in the spinel prepared by precipitation at 348 K and calcination at 773 K. This spinel also had the lowest initial temperature of reduction (TPR).