Nickel Particle Size Research Articles

Deposition of Ni nanoparticles onto porous supports using supercritical CO2: effect of the precursor and reduction methodology.

The deposition of Ni nanoparticles into porous supports is very important in catalysis. In this paper, we explore the use of supercritical CO(2) (scCO(2)) as a green solvent to deposit Ni nanoparticles on mesoporous SiO2 SBA-15 and a carbon xerogel. The good transport properties of scCO(2) allowed the efficient penetration of metal precursors dissolved in scCO(2) within the pores of the support without damaging its structure. Nickel hexafluoroacetylacetonate hydrate, nickel acetylacetonate, bis(cyclopentadienyl)nickel, Ni(NO(3))2⋅6H(2)O and NiCl(2)⋅6H(2)O were tried as precursors. Different methodologies were used: impregnation in scCO(2) and reduction in H(2)/N(2) at 400°C and low pressure, reactive deposition using H(2) at 200-250°C in scCO(2) and reactive deposition using ethanol at 150-200°C in scCO(2). The effect of precursor and methodology on the nickel particle size and the material homogeneity (on the different substrates) was analysed. This technology offers many opportunities in the preparation of metal-nanostructured materials.

Comparative study of electroless nickel film on different organic acids modified cuprammonium fabric (CF)

Nickel films were grown on citric acid (CA), malic acid (MA) and oxalic acid (OA) modified cuprammonium fabric (CF) substrates via electroless nickel deposition. The nickel films were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their individual deposition rate and electromagnetic interference (EMI) shielding effectiveness (SE) were also investigated to compare the properties of electroless nickel films. SEM images illustrated that the nickel film on MA modified CF substrate was smooth and uniform, and the density of nickel nuclei was much higher. Compared with that of CA modified CF, the coverage of nickel nuclei on OA and MA modified CF substrate was very limited and the nickel particles size was too big. XRD analysis showed that the nickel films deposited on the different modified CF substrates had a structure with Ni (111) preferred orientation. All the nickel coatings via different acid modification were firmly adhered to the CF substrates, as demonstrated by an ultrasonic washing test. The result of tensile test indicated that the electroless nickel plating on CF has ability to strengthen the CF substrate while causes limited effect on tensile elongation. Moreover, the nickel film deposited on MA modified CF substrate showed more predominant in EMI SE than that deposited on CA or OA modified CF.

Synthesis of coatings from nanocarbon fibers on sorption-inert surfaces

Method of catalytic dehydrogenation of hydrocarbons to obtain nanocarbon fibers directly on the surface of an inert macroporous support is considered. It is shown that nickel compounds can be uniformly deposited onto the surface of a support from aqueous solutions by the homogeneous deposition method, which provides a nickel particle size necessary for the subsequent growth of nanocarbon fibers. The specific features and limitations of the method are discussed.

Effects of Nickel Particle Size and Graphene Support on the Electrochemical Performance of Lithium/Dissolved Polysulfide Batteries

The electrocatalytic effect of nickel (Ni) nanoparticle sizes on the lithium polysulfide conversion reactions in dissolved lithium sulfur battery configuration is investigated. The Ni particles of 20nm with the higher cathode surface area show a superior capacity of 1066mAhg−1 sulfur compared to Ni particles of 40 and 100nm for the first cycle. In addition, to further improve the capacity retention and discharge capacity of the cell, the effect of the graphene support on Ni nanoparticle dispersion and cycling performance is investigated. The results show a significant improvement in the discharge capacity compared to the other electrodes. This could be explained by the homogeneous distribution of Ni nanoparticle within the carbon matrix, which suppress the agglomeration and surface area loss of the Ni nanoparticle after cycling; as well as a synergetic effect of graphene structure and Ni nanoparticle.

Influence on nickel particle size on the hydrodeoxygenation of phenol over Ni/SiO2

Hydrodeoxygenation (HDO) of phenol over nickel nano-particles of different size (5–22nm) supported on SiO2 has been investigated in a batch reactor at 275°C and 100bar. Deoxygenation was only observed as a consecutive step of initial hydrogenation of phenol at the given conditions. Both the hydrogenation and deoxygenation reaction were found to be Ni-particle size dependent. Rapid hydrogenation of phenol to cyclohexanol was achieved over the catalysts with large particles, while the rate of deoxygenation of cyclohexanol was slow. For the catalysts with small Ni particles, the opposite behavior was observed Specifically, the turn over frequency (TOF) of hydrogenation was 85 times slower for 5nm particles than for 22nm particles. On the contrary, the TOF of cyclohexanol deoxygenation increased by a factor of 20 when decreasing the particle size from 20nm to 5nm. A simple kinetic model showed that the rate limiting step for phenol HDO shifted from deoxygenation to hydrogenation when the particle size was below 9–10nm. Surface site population theory evidenced that the deoxygenation reactions were favored on step/corner sites, giving higher deoxygenation rates at small particles. For hydrogenation, the influence of particle size on the rate could be related to the size of the Ni facets with larger facets thus being better.

Coking resistance evaluation of tar removal catalysts

The tendency towards coke formation on nickel catalysts supported on hexaaluminates of barium, lanthanum and lanthanum/cerium was evaluated by two different methods: model reaction of cyclohexane dehydrogenation and thermogravimetric analysis using a synthetic gas composition. The ratio between hydrogenolysis and dehydrogenation rates provided a good indication of the potential for coke formation on the catalyst and is correlated to the nickel particle size. Thermogravimetric analysis was performed using a synthetic mixture containing H2, CO, CO2 and CH4, and also in the presence of C2H4. The catalyst supported on barium hexaaluminate presented lower coking rate and higher activity in toluene steam reforming, with preferential formation of filamentous carbon.

CO2 Hydrogenation Over Ni-Based Zeolites: Effect of Catalysts Preparation and Pre-reduction Conditions on Methanation Performance

In this work, CO2 methanation reaction was studied on Ni-based zeolite catalysts, which were prepared by incipient wetness impregnation of USY zeolite with 5 wt% Ni. The effects of the drying method after impregnation, the calcination temperature and the pre-reduction temperature on the catalysts performances were evaluated. The catalysts were characterized by N2 adsorption, hydrogen temperature programmed reduction, diffuse reflectance UV–Vis spectroscopy (DRS UV–Vis), transmission electron microscopy and X-ray diffraction. Drying under microwaves irradiation induced remarkable changes on the type, location and reducibility of Ni species at the same time that leaded to effects in the structural and textural properties of the support and in the average nickel particle size. As a result, changes in the catalytic performances were observed. The calcination temperature changed the location and reducibility of the Ni species being concluded that calcining at 300 °C leads to higher conversions and selectivities. At high reduction temperatures the amount of reduced Ni species (active sites) was greater, but the impact of sintering processes was also stronger. For catalysts with 5 % Ni, the reduction at 550 °C was observed as the most favourable. However for 14 % Ni sample no remarkable effects were observed by reducing at higher temperatures. Thus, it was proved that CO2 conversion and CH4 selectivity can be maximised through the proper choice of both preparation and pre-reduction conditions.

Influence of Ce-precursor and fuel on structure and catalytic activity of combustion synthesized Ni/CeO2 catalysts for biogas oxidative steam reforming

A series of nanosized Ni/CeO2 catalysts were prepared by Solution Combustion Synthesis (SCS) varying the fuel (oxalyldihydrazide, urea, carbohydrazide and glycerol), the cerium precursor (cerium nitrate and cerium ammonium nitrate) and the nickel loading (ranging between 3.1 and 15.6 wt%). The obtained powders were characterized by X-ray Diffraction (XRD), N2-physisorption, CO-chemisorption, Temperature Programmed Reduction (H2-TPR) and Scanning Electron Microscopy (SEM). The catalytic activity towards the Oxy Steam Reforming (OSR) of biogas was assessed. The selected operating variables have a strong influence on the nature of combustion and, in turn, on the morphological and structural properties of the synthesized catalysts. Particularly, the use of urea allows to improve nickel dispersion, surface area, particle size and reducibility of the catalysts, affecting positively the biogas OSR performances.

Fabrication of a Ni/MgO Nanocomposite Catalyst by Exolution

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems. In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern. In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes. Figure 1

Effect of support composition on the origin and reactivity of carbon formed during dry reforming of methane over 5 wt% Ni/Ce1−xMxO2−δ (M = Zr4+, Pr3+) catalysts

Carbon dioxide reforming of methane to synthesis gas in the 550–750°C range over 5wt% Ni/Ce1−xMxO2−δ (M=Zr4+, Pr3+) solids has been investigated with respect to the effects of support chemical composition and reaction temperature on the amount, reactivity (towards H2 and O2) and relative contribution of CH4 and CO2 activation routes towards “carbon” formation. For these “carbon” characterisation studies, various transient isothermal and temperature-programmed oxidation (TPO) and hydrogenation (TPH) experiments coupled with the use of 13CO and 13CO2 isotope gases were conducted. TPO following dry reforming (5%13CO2/5%12CH4/45%Ar/45%He) demonstrated that the relative amount of the various kinds of “carbon” formed via the CH4 and CO2 activation routes was strongly dependent on reaction temperature and support chemical composition. At 550°C, the ratio of 12CO2 to 13CO2 of the 12C-containing and 13C-containing inactive “carbon” formed was 0.4, 0.27 and 0.19, whereas at 750°C was 1.07, 1.06 and 0.29, respectively, for the 5wt% Ni supported on Ce0.8Zr0.2O2, Ce0.8Pr0.2O2 and Ce0.5Zr0.5O2 carriers. The origin of “carbon” formation via the CO2 activation route was illustrated to be the Boudouard reaction (2CO-s→CO2(g)+C-s+s) through a transient isotopic experiment with a feed gas containing 13CO and 12CH4. It was also found that CO-s derived from the direct dissociation of CO2 and the CH4 activation route can lead to a number of different kinds of “carbon” which depends on support chemical composition. The present 5wt% Ni/Ce0.8Pr0.2O2 catalytic system exhibited CO2 conversion of 84%, H2-yield of 48%, and H2/CO ratio of 1.04 after 50h of dry reforming of methane at 750°C (20% CH4, 20% CO2, He; GHSV=30,000h−1) with a relatively low amount (17.5mgC/gcat or 1.75wt%) of accumulated inactive “carbon”. The support chemical composition was found to influence the nickel particle size, which in turn influenced the origin, kinetics and the reactivity of “carbon” deposition under dry reforming reaction conditions.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous Ni/Al2O3 catalyst prepared by an EDTA-assisted impregnation method

A mesoporous alumina (denoted as MA) support was prepared by an epoxide-driven sol-gel method. A mesoporous Ni/Al2O3 catalyst was then prepared via impregnation of Ni(EDTA)2− complex anions onto positively-charged mesoporous alumina support (denoted as NiE/MA). For comparison, a mesoporous Ni/Al2O3 catalyst was also prepared by introducing nickel species onto MA support via conventional impregnation method (denoted as Ni/MA). Both NiE/MA and Ni/MA catalysts were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG) in order to investigate the effect of preparation method on the catalytic performance. Ni/MA catalyst retained relatively large amount of nickel species in the form of bulk nickel oxide, which were weakly bound to alumina support compared to NiE/MA catalyst. It was found that the reduced NiE/MA catalyst showed smaller metallic nickel particle size and higher nickel dispersion than the reduced Ni/MA catalyst, implying that NiE/MA catalyst retained stronger resistance toward nickel sintering than Ni/MA catalyst during the reduction process. It was also revealed that methane adsorption capacity of the reduced NiE/MA catalyst was larger than that of the reduced Ni/MA catalyst. NiE/MA catalyst with larger methane adsorption capacity exhibited better catalytic performance than Ni/MA catalyst in the hydrogen production by steam reforming of LNG.

Preparation of highly active and stable NiO–CeO2 nanocatalysts for CO selective methanation

In the present work, a group of nickel-ceria nanocatalysts was synthesized by co-precipitation method and their catalytic performances were considered in CO methanation reaction. The catalysts were characterized by XRD, BET, SEM, TEM, H2-TPR, CO chemisorption and CO-TPD techniques. The results showed that addition of nickel content up to 50 wt.% increased both the CO conversion and CH4 selectivity at low temperatures while further increase in nickel content adversely affected them. The 50%Ni/CeO2 catalyst revealed an excellent activity in CO methanation due to high surface area (258 m2/g), small nickel particle size (below 5 nm) and high metal dispersion (7.31%). In CO selective methanation, CO2 conversion was completely suppressed until CO conversion reached to a maximum value, which is an important factor from commercial view point where is needed to extend operating temperature window between maximum of CO conversion and suppressing of CO2 methanation.

Selective nickel-catalyzed conversion of model and lignin-derived phenolic compounds to cyclohexanone-based polymer building blocks.

Valorization of lignin is essential for the economics of future lignocellulosic biorefineries. Lignin is converted into novel polymer building blocks through four steps: catalytic hydroprocessing of softwood to form 4-alkylguaiacols, their conversion into 4-alkylcyclohexanols, followed by dehydrogenation to form cyclohexanones, and Baeyer-Villiger oxidation to give caprolactones. The formation of alkylated cyclohexanols is one of the most difficult steps in the series. A liquid-phase process in the presence of nickel on CeO2 or ZrO2 catalysts is demonstrated herein to give the highest cyclohexanol yields. The catalytic reaction with 4-alkylguaiacols follows two parallel pathways with comparable rates: 1) ring hydrogenation with the formation of the corresponding alkylated 2-methoxycyclohexanol, and 2) demethoxylation to form 4-alkylphenol. Although subsequent phenol to cyclohexanol conversion is fast, the rate is limited for the removal of the methoxy group from 2-methoxycyclohexanol. Overall, this last reaction is the rate-limiting step and requires a sufficient temperature (>250 °C) to overcome the energy barrier. Substrate reactivity (with respect to the type of alkyl chain) and details of the catalyst properties (nickel loading and nickel particle size) on the reaction rates are reported in detail for the Ni/CeO2 catalyst. The best Ni/CeO2 catalyst reaches 4-alkylcyclohexanol yields over 80 %, is even able to convert real softwood-derived guaiacol mixtures and can be reused in subsequent experiments. A proof of principle of the projected cascade conversion of lignocellulose feedstock entirely into caprolactone is demonstrated by using Cu/ZrO2 for the dehydrogenation step to produce the resultant cyclohexanones (≈80 %) and tin-containing beta zeolite to form 4-alkyl-ε-caprolactones in high yields, according to a Baeyer-Villiger-type oxidation with H2 O2 .

Effects of reduction process on the electrochemical and microstructural properties for electrolyte-supported SOFC

Reduction process plays an important role before solid oxide fuel cells (SOFCs) start to work. The reduced anode must have enough porosity for transferring the fuel gases and good conductivity for decreasing the area specific resistance. To investigate how the reduction process affects the electrochemical and microstructural properties for electrolyte-supported SOFC with a nickel oxide/yttria-stabilized zirconia (NiO/YSZ) anode, three different reduction processes are applied to the same batch of cells in this paper. Process I for one of tested cells is to introduce a dilute gas of 20% hydrogen and 80% nitrogen to the anode side at room temperature. Process II and III for the others are to introduce the same dilute gas while the cells are heated up to 800 and 700 °C respectively. Although the Process I provides much time to reduce the anode of the cell, the resulting performance is lower than the others. AC impedance analyses show that the cell reduced at higher temperature has lower ohmic and polarization resistance. Moreover, the differences of nickel connection and particle size on the anode are observed in microstructure of the cells, which proves that reduction process has a vital effect for solid oxide fuel cells.

Magnetic properties of nickel nanoparticles embedded in amorphous Al2O3 matrix

Multilayer thin films consisting of 10 bilayers of (Al2O3+Ni)/Al2O3 were deposited by magnetron sputtering onto Si(100) substrate. Nickel nanoparticles are formed inside amorphous alumina matrix by self-assembly growth process. It was determined by GISAXS measurements that nickel particles are spheroidal with diameter < 3 nm and that they form paracrystal-like body-centered tetragonal lattice. Magnetic properties of the prepared thin films were studied. Due to the nanometer size of nickel particles, their magnetic structure is single domain and they show superparamagnetic behaviour. Anisotropy of magnetic properties was observed when magnetic field is applied parallel or perpendicular to the thin film surface and it was attributed to dipole-dipole interactions between particles. This was confirmed using simulations of the M(H) curve of the 2D superlattice of the identical superparamagnetic particles, which was performed using Monte Carlo method and Metropolis algorithm.

Remarkable effect of soft-templating synthesis procedure on catalytic properties of mesoporous carbon supported Ni in hydrodechlorination of trichloroethylene in liquid phase

Ordered mesoporous carbon (CST-A) obtained by soft-templating method under acidic condition was used for preparation of nickel containing catalyst by incipient wetness impregnation with an aqueous solution of NiCl2·6H2O. The reduction of as prepared catalysts by 10% H2/Ar at 673K led to formation of well dispersed active metallic phase with average nickel particles size ∼11nm. 2wt.% Ni/CST-A was examined as a catalyst in hydrodechlorination (HDC) of trichloroethylene in liquid phase, without presence of an additional organic solvent in the reaction mixture. Ethane and ethylene were the predominant product of reaction. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies for catalysts after reduction and after HDC reaction indicated that use of hydrophobic, mesoporous active carbon as the support for nickel led to formation of resistant for sintering and leaching catalyst and the effective material for catalytic removal of trichloroethylene from water. Post-reaction deposits investigated by the temperature programmed hydrogenation (TPH) showed substantial amounts of carbon-containing deposit, with C2-hydrocarbons desorbing at a relatively low temperature (∼650K).

Effect of Morphology and Size of Nickel Particles on Electrochemical Performance of Sodium Metal Chloride Rechargeable Battery

Because of the limitation of lithium resources, sodium-based rechargeable batteries started to emerge as potential candidates for medium and large-scale stationary energy storage system (ESS) again. Na-S batteries have been used for large-scale stationary ESS but intrinsically have a risk for explosion. Sodium metal chloride batteries based on Na-NiCl2 chemistry, however, are consisted of safer electrode configuration with nickel, NaCl and NaAlCl4 as cathode ingredients than the Na-S batteries. The Na-NiCl2 batteries offer many attractive properties such as high cell voltage, high theoretical specific energy, and broad range in operating temperature. The nickel chloride electrode plays an important role in the cell performance. A qualitative and quantitative understanding of the electrochemical and morphological properties of NiCl2, therefore, is very important. This paper will describe effect of morphology and size of nickel particles on electrochemical performance of the sodium metal chloride batteries including synthesized nickel powders having very high porosity.

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY(2)O(3)-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/gamma-Al2O3 catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H-2-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH4 conversion increased with elevating levels of Y2O3 from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY(2)O(3)-Al2O3 catalysts maintained high activity after 24 h on stream, while Ni/Al2O3 had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Highly Dispersed Nickel-Containing Mesoporous Silica with Superior Stability in Carbon Dioxide Reforming of Methane: The Effect of Anchoring.

A series of nickel-containing mesoporous silica samples (Ni-SiO2) with different nickel content (3.1%–13.2%) were synthesized by the evaporation-induced self-assembly method. Their catalytic activity was tested in carbon dioxide reforming of methane. The characterization results revealed that the catalysts, e.g., 6.7%Ni-SiO2, with highly dispersed small nickel particles, exhibited excellent catalytic activity and long-term stability. The metallic nickel particle size was significantly affected by the metal anchoring effect between metallic nickel particles and unreduced nickel ions in the silica matrix. A strong anchoring effect was suggested to account for the remaining of small Ni particle size and the improved catalytic performance.

Diameter-controlled carbon nanotubes and hydrogen production

Simultaneous production of hydrogen and carbon nanomaterials over Ni-loaded ZSM-5 catalysts via catalytic decomposition of methane was investigated. The effects of nickel particle size and reaction temperature on the hydrogen production, catalyst deactivation and the morphologies of the carbon nanotubes were investigated. Two catalyst were prepared: Ni/ZSM-5(300) – predominant size of the Ni particles 30–60 nm and nNi/ZSM-5(300) predominant size of the Ni particles 10–20 nm.The carbon nanotubes and nanofibers diameters produced over Ni/ZSM-5(300) was equal to 20–57 nm depending on the temperature. The average diameter of carbon nanomaterials obtained over nNi/ZSM-5(300) was about 15 nm regardless the temperature.Catalyst Ni/ZSM-5(300) was effective for the production of hydrogen via the methane decomposition at the temperature range 650–700 °C (constant hydrogen concentration about 55%).