Nano-sized Ni Particles Research Articles

Microwave-activated Ni/carbon catalysts for highly selective hydrogenation of nitrobenzene to cyclohexylamine

Biocarbon supported Ni catalysts have been prepared by facile impregnation of Ni species by microwave-heating and used for selective hydrogenation of nitrobenzene to cyclohexylamine. These catalysts were characterized by X-ray diffraction, Raman spectra, N2 sorption measurement, X-ray photoelectron spectroscopy, temperature programmed reduction of H2 and H2 temperature-programmed desorption. The morphology and particle size of catalysts were imaged by scanning electron microscope and transmission electron microscope. For the hydrogenation of nitrobenzene to cyclohexylamine, 10%Ni/CSC-II(b) exhibits the best catalytic activity to achieve 100 mol% conversion of nitrobenzene and 96.7% selectivity of cyclohexylamine under reaction conditions of 2.0 MPa H2 and 200 °C, ascribed to high dispersion of Ni species and formation of nanosized Ni particles on the support aided by microwave-heating. Thus-prepared Ni/CSC catalyst is greatly activated, in which the addition of precious metal like Rh is totally avoided.

Synthesis of Ni-CeO2 catalyst for the partial oxidation of methane using RF thermal plasma

Ni-CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni-CeO2 catalysts, a precursor containing Ni (∼5-μm diameter) and CeO2 (∼200-nm diameter) powders were heated simultaneously using an RF plasma at a power level of ∼52 kVA and a powder feeding rate of ∼120 g/h. From the X-ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles (<–50-nm diameter) on their surfaces. The catalytic performance was evaluated under atmospheric pressure at > 500 °C and a CH4:O2 molar ratio of 2:1 with Ar diluent. Although the Ni content was high (∼50 mol%), the experimental results reveal a methane conversion rate of > 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on-stream test at 550 °C for 24 h. However, at 750 °C, the on-stream test revealed the formation of filament-like carbons with an increased methane conversion rate over 90%.

Enhancing the Stability of Infiltrated Ni/YSZ Anodes

One of the challenges related to Ni-based anodes in solid oxide fuel cells (SOFCs) is their dimensional instability, especially when they are exposed to air and then back to fuel, which is called redox cycling. One possible solution to this problem is the fabrication of a pre-sintered porous electrolyte matrix, followed by infiltration of 10-20 vol% of the active materials into this scaffold. However, this can lead to instability of the infiltrated particles as a result of sintering of the infiltrated phase at SOFC working temperatures. This problem is very severe when depositing nano-sized infiltrated metal particles on the oxide ceramic backbone. In this study, Ni-containing solutions were infiltrated into a symmetrical tubular half-cell, fabricated by slip-casting, composed of two porous yttria-stabilized zirconia (YSZ) layers, separated by a 50 μm dense YSZ electrolyte. A combination of electrochemical impedance spectroscopy (EIS) and electron microscopy imaging has been used to determine long term stability of the cells. It was found that the amount of infiltrated Ni has a significant impact on the long term stability of the Ni/YSZ anodes. This can be explained by the better connectivity between Ni particles even after long term testing when there is more Ni in the structure. It was also demonstrated that high temperature treatment of the infiltrated Ni/YSZ anodes just after the first few infiltrations, followed by several further Ni infiltration steps, has a significant effect not only on the stability of the anode at 800 C, but also on the anode performance. As the YSZ backbone has the ability to dissolve NiO at higher temperatures, the dissolved NiO can be ex-soluted in the form of nano-sized Ni particles at cell working temperatures and under reducing atmospheres. This effect was also investigated using electron microscopy, revealing the size and shape of the ex-soluted Ni particles, especially after long term testing. Finally, the effect of infiltration of cerium oxide prior to Ni infiltration on the stability of the anodes was also investigated. As the wettability of Ni particles on a reduced ceria surface is different from non-reduced ceria, the sintering behaviour of Ni on these two surfaces was found to be different as well.

Enhancing the Stability of Infiltrated Ni/YSZ Anodes

One possible solution to the redox cycling problem in Ni-based anodes is the fabrication of a pre-sintered porous electrolyte matrix, followed by infiltration of 10-20 vol% of a Ni-based catalyst into this scaffold. However, this can lead to instability as a result of sintering of the infiltrated phase at SOFC working temperatures. In this study, various Ni-containing solutions were infiltrated into a symmetrical tubular half-cell, with electrochemical impedance spectroscopy (EIS) and electron microscopy imaging used to determine the long term stability of the cells. It was found that the amount of infiltrated Ni has a significant impact on the long term stability of the Ni/YSZ anodes, explained by the better connectivity between Ni particles when there is more Ni present. It was also demonstrated that high temperature treatment of the infiltrated Ni/YSZ anodes just after the first few infiltrations, followed by several further Ni infiltration steps, has a significant effect not only on the stability of the anode at 800 oC, but also on the anode performance. As the YSZ backbone has the ability to dissolve NiO at higher temperatures, the dissolved NiO can be ex-soluted in the form of at least partially inter-connected nano-sized Ni particles at cell working temperatures under a reducing atmosphere.

Nanostructured Ni-YSZ Anode By Atomic Layer Deposition for Solid Oxide Fuel Cells

Nickel yttria-stabilized zirconia (Ni-YSZ) is the most commonly used anode for solid oxide fuel cells (SOFCs). The electrochemical performance of Ni-YSZ anodes can be improved when the size of constituent particles is reduced. However, under SOFC operating environment, nano-sized Ni particles suffer from sintering; nanoscale Ni-YSZ anodes can undergo structure changes, which constrain the development of nanoscale Ni-YSZ anodes. In this work, nanoscale nanostructured Ni-YSZ anode was successfully fabricated by combining atomic layer deposition (ALD) and glancing angle deposition (GLAD). Prior to atomic layer deposition of YSZ, the porous Ni nanorod electrode was firstly prepared by GLAD. ALD was applied to deposit a uniform nanoscale YSZ coating layer over the nickel nanorods. The morphology of the nanostructured Ni-YSZ anode was examined with scanning electron microscopy (SEM). The surface area was increased to more than 3 times as large as plane area and the triple phase boundary (TPB) extended to the entire nickel surface. The surface composition was examined with X-ray photoelectron spectroscopy (XPS). The atomic composition of YSZ film was controlled by the ALD process and not affected by the post-deposition annealing process. ALD coating approach combined ionic conductive YSZ electrolyte phase with electrical conductive Ni phase flexibly and controlled the porosity of the nano-composite electrode just through deposition and post-deposition annealing process. Electrical conductivity measurements were performed using a 4-point probe method. The Ni-YSZ anodes maintained resistivity in the 10-4 cm·S-1 magnitude, which is sufficiently conductive as an SOFC anode. The ALD YSZ coating layer showed sintering-resistance on the nanostructured electrode with an as thin as 1.9 nm YSZ coating layer and excellent anode performance under SOFC operating conditions.

Nanostructured Ni-YSZ by Atomic Layer Deposition

Nickel yttria-stabilized zirconia (Ni-YSZ) is used as anode material for solid oxide fuel cells (SOFCs). The electrochemical performance of Ni-YSZ anodes can be improved when the size of constituent particles of nickel is reduced. However, at SOFC high temperature operating environments, nano-sized Ni particles suffer from sintering. Nanoscale Ni-YSZ anodes can undergo severe structure changes. In this work, a unique approach of fabricating a nanostructured Ni-YSZ anode is demonstrated by combining atomic layer deposition (ALD) and glancing angle deposition (GLAD) techniques whereby nickel nanoparticle sintering is prevented at high temperatures with as thin as 1.9 nm YSZ ALD coating on the nickel; the surface area of the resulting Ni-YSZ anode was found to increase more than 3 times that of a planar electrode. In addition, the novel ALD/GLAD coating approach used here provides an ionic conductive YSZ electrolyte phase combined with an electrical conductive Ni phase whereby porosity can be controlled through deposition and post-deposition annealing. In addition, the surface roughness of Ni-YSZ anode decreases with increasing YSZ coating layer thickness and it is unaffected by the post-deposition annealing process. Conductivity measurements of the Ni-YSZ anodes at room temperature show a resistivity in the order of 10−4 cm·S−1.

In-situ catalytic growth of MgAl2O4 spinel whiskers in MgO–C refractories

Abstract Upon application of nano-sized metallic Ni particles as catalyst, the in-situ synthesis mechanism of spinel whiskers in MgO–C refractories was studied. Their phase composition and morphology were determined by means of X-ray diffraction and scanning electron microscopy supported by energy dispersive spectroscopy. The results show that when the catalyst of nano-sized Ni was added in MgO–C refractories, the granular MgAl2O4 (MA) spinels transformed into the shape of whiskers at 1 200 °C. The presence of Ni catalyst can accelerate the generation of Mg vapor, which can react with Al vapor to form MA spinel whiskers. Through dissolution and precipitation, MA spinel crystals nucleate directly and grow into whiskers from the catalytic droplets of nano-sized metallic Ni particles. The growth of spinel whiskers follows a typical vapor–liquid–solid (V–L–S) growth mechanism.

A Nanoarchitectured Porous Electrode Assembly of NiSi Thin Film for Lithium Ion Batteries

This study proposes to produce well-aligned nanorod arrays containing NiSi thin film to improve the electrochemical performance of Si based anodes. In this respect, NiSi thin films made of nanorods are produced via glancing angle electron beam deposition (GLAD) technique. The structural and morphological properties are investigated using thin film X-ray diffraction (XRD) and scanning electron microscopy (SEM). The well aligned nanorod arrays containing NiSi thin film anode exhibits a long cycle life with a moderate capacity retention (around 1100mAhg-1 for 100 cycles). This remarkable electrochemical performance can be explained by the electrode composition, structure and morphology: During Li+ insertion into the alloyed thin film electrodes, Si acts as active center, which reacts with Li+ to form amorphous LixSi alloys, while the nanosized Ni particles are believed to provide electrical conduction network inside the active material and buffer volume expansions with the help of the homogenously distributed nanosized interspaces (porosities among the nanorods) present in the thin film.

Highly dispersed β-NiS nanoparticles in porous carbon matrices by a template metal–organic framework method for lithium-ion cathode

By calcination of MOF-74(Ni) under reducing environments, nanosized Ni particles (5–10 nm) in carbon matrices were obtained, which were converted into NiS through an in situ reaction. Featuring small particle sizes (∼50 nm), uniform distribution and porosity, C ⊃ NiS was preliminarily studied as lithium-ion cathode material, which has shown electrochemical performance superior to that of bare NiS.

Metal-polymer nanocomposites with high percolation threshold and high dielectric constant

By combining a solution cast and a hot-press process, a process to prepare uniform metal-polymer nanocomposites is introduced. It is confirmed using two composite systems: nanosized Ni particles embedded into P(VDF-TrFE) 70/30 mol. % and P(VDF-CTFE) 88/12 mol. % copolymer, respectively. Composites with 0 vol. %–60 vol. % of Ni nanoparticles are studied. The dielectric property of each composite is characterized over a frequency range from 100 Hz to 1 MHz. The results show that two nanocomposite systems show very similar percolation behavior with a high percolation threshold (&amp;gt;55 vol. %) and exhibit a high dielectric constant (∼1000 at 100 Hz).

Chemical synthesis and characterization of manganese oxide coated Ni particles

Nanosized Ni particles with an average diameter of about 8 nm were prepared by reducing of NiCl2 with sodium borohydride (NaBH4) in aqueous solution. By moderate annealing in protective atmosphere, the composite grew up to be 15–20 nm particles. Both of the as-prepared and annealed Ni particles were coated by a layer of manganese oxide via decomposition reaction in aqueous KMnO4 solution. Hysteresis loops of as-prepared samples show a large increase in the magnetization with decreasing temperature and an unsaturated component at high magnetic field. In contrast, the ferromagnetic characteristics of annealed one are much stronger with large magnetization and coercivity. The thermomagnetic curves verified the coexistence of ferromagnetic Ni and antiferromangetic Mn oxide phases. But there exists no exchange bias behavior in the samples, even though the interface structure between the ferromagnetic Ni core and the antiferromagnetic manganese oxides has been distinctly formed. The absence of exchange bias probably originates from the weak ferromagnetic characteristic of Ni cores.

Catalytic Nonthermal Plasma Reactor for Dry Reforming of Methane

Co-processing of two greenhouse gases, methane and carbon dioxide, was carried out in a dielectric barrier plasma reactor. The influence of feed gas proportion on the performance of the plasma reactor was investigated, especially with an objective to increase the conversion of the reactants and selectivity to syngas. To understand the influence of the catalyst on dry reforming, 10–30% NiO/Al2O3 catalysts were prepared by a single-step combustion synthesis and various physicochemical techniques confirmed the formation of nanosized Ni particles. A total of 10% of the discharge volume was packed with Ni/Al2O3 catalysts in a packed-bed configuration. An interesting observation is the increased syngas selectivity on the addition of catalyst to plasma, and among the catalysts tested, 20% Ni showed a H2/CO ratio of 2.25 against 1.2 with a plasma reactor alone.

The influence of addition of nanosized molybdenum and nickel particles on creep behavior of Sn–Ag lead free solder alloy

The effect of addition of nano-sized Ni and Mo particles on creep behavior of Sn–3.5Ag lead free solder alloy was investigated using a constant load method in a nanoindenter. Modified Garofalo’s equation was found to show an excellent fit to indentation creep data. It was observed that the steady state creep rate as well as primary creep stage displacement and primary creep stage time decreased with increasing addition of Mo and Ni to the base alloy.

Synthesis and Characterization of Ni/CNTs Electrodes and their Supercapacitors Performance

The Ni/Carbon nanotubes (CNTs) composites for supercapacitor electrode have been synthesized by electroless deposition method. The morphology and structure of Ni/CNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nano-size Ni particles coated the surface of carbon nanotubes. Electrochemical performances of the synthesized composites were investigated by cyclic voltammetry and galvanostatic charge/discharge measurement. The specific capacitance of prepared electrode is up to 281 F/g, which is much higher than acetylene black electrode and pure carbon nanotubes electrode, indicating an effective path for increasing specific capacitance of carbon materials for the appplication of supercapacitors.

H2 Production with Low CO Selectivity from Photocatalytic Reforming of Glucose on Ni/TiO2-SiO2

Nano-sized Ni particles on TiO2-SiO2 were synthesized by the two methods of photo-assisted deposition (PAD) and impregnation. H2, which is a promising energy carrier, with a low CO concentration was produced by the photocatalytic reforming of glucose (a model biomass) on the Ni/TiO2-SiO2 catalyst. The supported Ni enhanced the rate of H2 production while it suppressed CO selectivity. The catalysts were characterized by X-ray diffraction, X-ray absorption fine structure, transmission electron microscope, and nitrogen adsorption analysis. Both H2 production and CO selectivity were strongly dependent on the preparation method, and PAD-Ni/TiO2-SiO2 was the better catalyst for H2 production with the lowest CO concentration.

Active phase evolution in single Ni/Al2O3methanation catalyst bodies studied in real time using combined μ-XRD-CT and μ-absorption-CT

A combination of synchrotron μ-XRD-CT and μ-absorption-CT (CT = computed tomography) is demonstrated, providing a unique insight into the solid state changes occurring from within crystalline materials. Specifically, we examine here the solid state changes that occur in a millimetre-sized Ni/γ-Al2O3 catalyst body in both 2D and 3D during calcination and CO methanation for the first time. The combination provides a unique insight into the spatial phase distribution of these materials and how these evolve via a series of solid state transformation processes. For example, initially, two Ni-ethylenediamine (en) complexes were observed on the impregnated and dried body; a hydrated and non-hydrated form, which 2D scans reveal possess an egg-shell and egg-yolk distribution, respectively. Furthermore, the μ-XRD data were of sufficient quality so as to be able to reveal that the particles within the ‘egg-shell’ were larger (∼35 nm) than those of the ‘egg-yolk’ (∼19 nm) and that there were more of them. On calcination, both precursors collapsed, yielding metallic fcc Ni particles with a surprisingly uniform average size distribution over the catalyst (∼4 nm). However, a comparison of the scattering at different stages of the experiment suggested that the crystalline structure of some of the Ni remained diffraction ‘silent’. Calcination in oxygen lead to both Ni oxidation and particle sintering, mainly at the exterior, which on pre-reaction reduction (in H2) yielded again fcc Ni particles (∼4 nm interior, ∼6 nm exterior) with a significant reduction in the amorphous Ni component. The catalyst proved active for CO methanation and, during 2 h time on-stream, no change in the structure composition or shape was observed, leading us to conclude that nano-sized fcc Ni particles on γ-Al2O3 are the active component in CO methanation. This work therefore demonstrates both the power of spatially resolved μ-XRD-CT/μ-absorption-CT measurement of catalytic systems and its advantage over more ‘traditional’ single point studies on small sieve fractions.

Charge Dependent Catalytic Activity of Gasborne Nanoparticles

It is shown experimentally that the electric charge of unsupported catalyst particles has a major influence on the methanation of CO with nano-sized Ni particles as catalyst at temperatures between 680 K and 720 K. Neutral particles showed an apparent activation energy of 148 kJ/mol, significantly higher than the apparent activation energies of 43 kJ/mol and 60 kJ/mol for negatively and positively charged particles, respectively. The obtained activation energies are comparable to energies obtained for different sites on alumina supported nickel catalysts. The change in activation energy can be qualitatively explained by different electron interchange between the chemisorbed species and the catalyst. We suggest that the observed effect of electron enhancement or depletion on catalysis is also a governing effect in strong metal support interaction (SMSI), where the displacement of electrons is related to the contact potential between catalyst and substrate.

Toughening and strengthening zirconia through the addition of a transient solid solution additive

Abstract A very small amount of nickel oxide (NiO), 0.18 mol%, could dissolve into yttria-stabilized zirconia (YSZ) during sintering in air at elevated temperature. The presence of Ni solutes enhances both the densification and grain growth of YSZ specimens. By heat-treating the NiO-doped YSZ specimen in a reducing atmosphere, nano-sized Ni particles are produced at the grain boundaries. The NiO thus acts as a transient solid solution additive for the YSZ-Ni nanocomposite. The formation of Ni nano-particles introduces an extra ferromagnetic performance into the YSZ specimen. Furthermore, the toughness and strength of YSZ are enhanced respectively by 120% and 40%. The toughness enhancement shows strong dependence on the size of ZrO 2 grains. Nevertheless, the strengthening is contributed by many factors.

Core/shell and multi-scale structures enhance the anode performance of a Sn–C–Ni composite thin film in a lithium ion battery

A Sn–C–Ni composite thin film has been prepared by electron beam evaporation using a TiNi alloy as a reaction medium. The thin film with a multi-scale structure is composed of lots of micro-sized core/shell particles. The cores are Sn single crystals and the shells are amorphous carbon with nano-sized Sn and Ni particles dispersed inside. Both the Sn core and the sp2 amorphous carbonaceous shells react with lithium and give substantial contributions to its total high capacities of 1200 mA h g−1 at C/3. The multi-scale structure of the Sn phases and the coating of nanocomposite carbonaceous shells on the Sn cores, as well as the dispersion of nano-sized Sn and Ni particles in the amorphous carbon matrix enhance the Li+ diffusion kinetics and the stability of the structure of the active materials, and thus the thin film electrode has good capacity retention and a high-rate capability (472 mA h g−1 at 12C).

Redox Stable Solid Oxide Fuel Cells with Ni-YSZ Cermet Anodes Prepared by Polymeric Precursor Infiltration

Redox stable SOFCs with Ni-YSZ cermet anodes were developed for electrolyte supported design (electrolyte thickness: 170 μm). Redox stable Ni-YSZ anode was prepared by infiltrating polymeric NiO precursor into pre-sintered porous YSZ layer (∼10 μm thick) followed by reduction ex situ. Polymeric precursor infiltration technique yielded a Ni-YSZ cermet microstructure with nanosized Ni particles coating the surface of porous YSZ. Low temperature processing of nanostructured Ni-YSZ cermet resulted in the reduction of internal stresses between Ni/NiO coating and YSZ skeleton during the redox cycling process. Electrolyte supported SOFC prepared with Ni-infiltrated anode showed a power density of ∼0.315 Watt.cm−2 and a highly redox stable anode (reduction of power density less than 1% after 15 redox cycles) in humidified forming gas (10%H2–90%Ar).