Nickel Particle Size Research Articles

Effect of Pr addition on the properties of Ni/Al2O3 catalysts with an application in the autothermal reforming of methane

Ni/xPr-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/γ-Al2O3 catalyst; the physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H2-temperature programmed reduction techniques (TPR). The results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al2O3 supports and the promotion of NiO reduction by Pr modification. The CH4 conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al2O3 catalysts maintained the high activity after 48 h while Ni/Al2O3 had a significant deactivation.

Nano to Micro Particle Size Distribution Measurement in the Fluid by Interactive Force Apparatus for Fine Particle Processing

The direct measurement of fine particles size distribution of dispersions or coagulations in liquid is important for water purification, fine particles separation for recycling and mineral processing, as well as the new material production. The nano to micro particle size is usually measured by light scattering method; however, it is difficult to measure at high concentration of suspension. Here, a novel dynamical method by using the interactive force measurement between particles in liquid under electric field is used for measuring distribution of fine particle. Three types of nano to submicron particles, that is well-dispersed nano particles, coagulated nano particles and settled submicron particles, have been measured by interactive force measurement method. The particle size distributions are compered with the size distributions of dried particles measured by TEM or SEM. The well-dispersed nano particle size distribution by interactive force measurement is influenced by the nano size surfactant micelles. The size distribution of coagulated nano particles in water is larger than the result by TEM. On the other hand, the submicron nickel particle size distribution is similar with the one analyzed by SEM.

Performance of Carbon Nanofiber and Activated Carbon Supported Nickel Catalysts for Liquid-Phase Hydrogenation of Cinnamaldehyde into Hydrocinnamaldehyde

The herringbone and platelet carbon nanofibers and the activated carbon were used as the supports of nickel catalyst for the selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde (HALD). The hydrogenation of HALD and cinnamyl alcohol under the same experimental conditions was also performed to determine the susceptibility of the isolated and conjugated C=O and C=C bonds to hydrogenation. The catalytic activity and selectivity of the nickel supported on carbons of different structure were evaluated based on the determination of the rate constants of the hydrogenation reaction. The nickel particle size effect was found to be crucial for the catalyst performance.

Comparative Study on Performance Stability of Ni–Oxide Cermet Anodes under Humidified Atmospheres in Solid Oxide Fuel Cells

The influence of the oxide component in Ni–oxide based cermet anodes on the performance stability was examined at 1000°C with a supply of highly humidified hydrogen, 40% H2O–60% H2. Three types of anodes were applied; Ni–samaria-doped ceria (Ni–SDC), Ni–yttria-stabilized zirconia (Ni–YSZ), and Ni–scandia-stabilized zirconia (Ni–ScSZ). Abrupt deterioration in performance was confirmed during constant current operation for the cells with Ni–YSZ and Ni–ScSZ anodes, accompanied with a drastic increase in ohmic resistance between the anode and reference electrode. In contrast, the performance of cell with Ni–SDC anode was pretty stable for 48 h. These differences in performance stability were significantly related to the local partial pressure of steam in the vicinity of the electrochemically active sites because the surface oxidation of nickel particles resulted in the deterioration. The microstructural changes in Ni–YSZ and Ni–SDC anodes upon discharge were also quantified by the dual–beam focused ion beam–scanning electron microscopy (FIB–SEM). The electrochemical behavior observed in each anode had a strong correlation with the anode microstructure such as triple phase boundary length and nickel particle size.

Effect of Phosphorus Amount on the Particle Size and Catalytic Performance of Heterogeneous Nickel(II) Schiff-Base Complex in Aldol Condensation Reaction

The organic–inorganic hybrid of citric acid, tetraethoxysilane (TEOS), and triethylphosphate (TEP) doped by a nickel Schiff-base complex was prepared by sol–gel method. The prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmittance electron microscopy (TEM), scanning tunnelling microscopy (STM), and infrared spectroscopy (IR). In order to determine the phosphorus amount effect on the catalytic activity of the prepared composites, the aldol condensation was used as a model reaction. The results revealed that the composite with 10% phosphorus is a better catalyst in comparison with other composites. [Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the following free supplemental files: Additional figures file.]

Hydrodechlorination of chlorobenzene in the presence of Ni/Al2O3 prepared by laser electrodispersion and from a colloidal dispersion

The low-percentage Ni/Al2O3 catalysts with active metal contents of 0.0002–0.1 wt % were prepared using the laser electrodispersion (LED) method and by means of supporting from a colloidal dispersion (CD). Their composition and physicochemical properties were determined by atomic absorption spectrometry, transmission electron microscopy (TEM), and XPS. With the use of TEM, it was found that average size of nickel particles in the LED catalysts was smaller than that in the CD catalysts. According to XPS data, the supporting of a metal onto a substrate by the LED method makes it possible to obtain samples containing Ni metal with a low active metal content (0.03 wt %). They exhibited a high initial activity in the hydrodechlorination reaction of chlorobenzene in a vapor phase, which was performed in a flow system at temperatures of 100–350°C. The CD catalysts were active in this reaction only at temperatures of 300–350°C. Reductive treatment led to the deactivation of LED catalysts and increased the activity and stability of samples prepared by supporting from a CD. The possible reasons for the observed changes are considered.

An egg-shell type Ni/Al2O3 catalyst derived from layered double hydroxides precursor for selective hydrogenation of pyrolysis gasoline

Egg-shell type catalysts, in which a thin layer of catalytically active component is distributed on the outer surface of the support particle, have been theoretically and experimentally proved to be useful in processes where the reaction has a very high rate and the intraparticle diffusion becomes the limiting step. Herein we report the preparation of an egg-shell Al2O3-supported nickel (Ni/Al2O3) catalyst derived from layered double hydroxides (LDHs) precursor, and its catalytic performance for selective hydrogenation of pyrolysis gasoline (PyGas), an important by-product of ethylene industry from thermal decomposition of heavier oil fractions, which was carried out in the liquid phase. Firstly, a Ni2+Al3+-containing LDHs (NiAl-LDHs) precursor was in situ grown on the surface of γ-Al2O3 spheres by using a diluted ammonia solution as precipitator. Then, egg-shell Al2O3-supported nickel oxide (NiO/Al2O3) sample with NiO crystallites highly dispersed on the external edge of the Al2O3 support was obtained after calcination at 450°C. The experimental study of selective hydrogenation of styrene (PyGas model 1) for revealing the intrinsic hydrogenation kinetics was carried out in a batch reactor at 60°C using the egg-shell Ni/Al2O3 catalyst (denoted LP-Ni/Al2O3; LP is expressed as layered precursor) fabricated by subsequent ex situ presufidation and final H2 reduction at 500°C of the NiO/Al2O3 sample. In addition, an Ni/Al2O3 catalyst with uniform distribution of Ni in the catalyst was prepared by a conventional wet impregnation method (denoted IM-Ni/Al2O3; IM is expressed as impregnation method) with the consistent Ni loading amounts and given into the consideration for comparison. The estimated effectiveness factor (η) of the LP-Ni/Al2O3 catalyst was higher than that of the IM-Ni/Al2O3 one, demonstrating the catalyst with egg-shell structure has a lower intraparticule mass transfer resistance. The catalytic hydrogenation activities of both Ni-based catalysts were further evaluated by selective hydrogenation of diolefins (PyGas model 2), along with selective hydrogenation of PyGas model 1, in a micro-flow reactor. The egg-shell Ni/Al2O3 catalyst derived from LDHs precursor exhibited a superior catalytic hydrogenation performance, which mainly be due to Ni metal being deposited on the Al2O3 support in a much thinner outer layer, as well as a smaller average size of nickel particles with stronger interaction between the nickel species and support. Several characterization techniques including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), low temperature N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction of hydrogen (TPR)/temperature programmed desorption of hydrogen (H2-TPD) were adopted to investigate the physical–chemical properties of the two supported Ni catalysts in detail.

Syngas production via CO2reforming of methane over plasma assisted synthesized Ni-Co/Al2O3-ZrO2nanocatalysts with different Ni-loadings

SUMMARY Ni-Co/Al2O3-ZrO2 nanocatalysts with 5, 10 and 15 wt.% nominal Ni content have been prepared by impregnation followed by a non-thermal plasma treatment, characterized and tested for dry reforming of methane. For nanocatalysts characterization the following techniques have been used: XRD, FESEM, TEM, EDX dot-mapping, BET, FTIR and XPS. The dry reforming of methane was carried out at different temperatures (550-850 °C) using a feed mixture of CH4:CO2 (1:1). Among the nanocatalysts studied, the catalyst with the medium Ni content (10 wt.%) was the most active in dry reforming of methane. This higher activity exhibited by Ni-Co/Al2O3-ZrO2 catalyst with medium Ni content (10 wt.% ) can be attributed to small and well dispersed particles of Ni within the catalyst. Apart from the narrow surface particle size distribution in the case of Ni(10 wt.%)-Co/Al2O3-ZrO2, the presence of small active components with average size of 7.5 nm is proposed to be the reason for the superior performance of the catalyst. Ni(10 wt.%)-Co/Al2O3-ZrO2 nanocatalyst had maximum surface area and the lower surface area was observed in the case of Ni(5 wt.%)-Co/Al2O3-ZrO2 and Ni(15 wt.%)-Co/Al2O3-ZrO2 due to the formation of the larger agglomeration and higher mean particle size of nickel particles, respectively. Although, GHSV enhancment had inverse effect on product yield but yield reduction for Ni-Co/Al2O3-ZrO2 catalyst with 10 wt.% Ni was less drastic at high GHSVs. According to XRD and XPS, existence of NiAl2O4 confirms strong interaction between Ni and support but higher loadings of Ni resulted in less NiAl2O4; loser interaction between support and active phase. Small particles of active components and well-defined dispersion of them in Ni(10 wt.%)-Co/Al2O3-ZrO2 nanocatalyst resulted in stability of the catalyst for either feed conversion or H2/CO molar ratio. Copyright © 2013 John Wiley & Sons, Ltd.

Catalytic activity of HAlBEA and NixHAlBEA zeolites in hydrogen-assisted dehydrochlorination of 1,2-dichloroethane into vinyl chloride monomer

HAlBEA zeolite is prepared by calcination of parent TEABEA zeolite at 823K for 3h in air following ionic exchange with NH4NO3 solution. NixHAlBEA zeolites are prepared by impregnation of HAlBEA with an aqueous solution of Ni(NO3)2, following a drying at 333K to obtain NixHAlBEA. The calcination of HAlBEA and NixHAlBEA at 773K for 3h in air leads to the formation of C-HAlBEA and C–NixHAlBEA with appeared, for the latter, an octahedral and tetrahedral Ni(II) species incorporated in BEA framework as evidenced by XRD, DR UV–vis and XPS. Red-C-HAlBEA and red-C–NixHAlBEA are investigated as the catalysts in dehydrochlorination of 1,2-dichloroethane into vinyl chloride monomer in the presence of hydrogen at 503–523K. Red-C-HAlBEA and red-C–Ni1.0HAlBEA show an excellent selectivity toward vinyl chloride (∼100%). Activity of HAlBEA and NixHAlBEA in the catalytic conversion of 1,2-dichloroethane strongly depends on the acidic properties of these materials and for the latter the catalytic activity depend on metal dispersion. The small Ni particles favor the dehydrochlorination of 1,2-dichloroethane to vinyl chloride. With increasing nickel particles size decreases activity of the red-C–NixHAlBEA catalysts. For these catalysts after kinetic run sintering of nickel phase is observed. Besides of carburization the nickel sintering is the main cause of red-C–NixHAlBEA deactivation. It is stronger for spent-red-C–Ni2.0HAlBEA with larger nickel particles than for red-C–Ni1.0HAlBEA containing smaller nickel particles (smaller than 5nm).

Hydrogen Production via Glycerol Steam Reforming over Ni/Al2O3: Influence of Nickel Precursors

This paper describes an investigation regarding the influence of Ni precursors on catalytic performances of Ni/Al2O3 catalysts in glycerol steam reforming. A series of Ni/Al2O3 is synthesized using four different precursors, nickel nitrate, nickel chloride, nickel acetate, and nickel acetylacetonate. Characterization results based on N2 adsorption–desorption, X-ray diffraction, H2 temperature-programmed reduction, H2 chemisorption, transmission electron microscopy, and thermogravimetric analysis show that reduction degrees of nickel, nickel dispersion, and particle sizes of Ni/Al2O3 catalysts are closely dependent on the anion size and nature of the nickel precursors. Ni/Al2O3 prepared by nickel acetate possesses the moderate Ni reduction degree, high Ni dispersion, and small nickel particle size, which possesses the highest H2 yield. Reaction parameters are also examined, and 550 °C and a steam-to-carbon ratio of 3 are optimized. Moreover, coke deposition, mainly graphite species, leads to the deactivation of Ni/Al2O3 catalysts in glycerol steam reforming. Nickel chloride-derived Ni/Al2O3 catalysts suffer from severe coke deposition and low reaction activity due to large Ni particle size, low Ni dispersion, and residual chloride.

Optimization on Selective Fiber Laser Sintering of Tri-Metallic Powders via Design of Experiments Method

The objective of this research is to investigate the effect of various parameters on rapid prototyping parts during the process of sintering metal powder by using fiber laser. In order to minimize the percentage of porosities of rapid prototyping (RP) products, sintering a mixture of three metallic powders are investigated. Three metallic powders which are used in this research are Cooper, Iron and Nickel (particle size of Cooper is 5μm, Iron is 70μm and Nickel is 70μm). In addition, control factors and their alternate levels-two levels with 48 run experiments will be identified. The Design of Experiment (DOE) and Analysis of Variance (ANOVA) are used to analyze the results of modeling process. After the ANOVA, a regression model predicting percentages of porosities under various conditions was developed when the traditional Taguchis approach failed to identify a feasible model due to strong interactions of controlled factors.

The Hydrodeoxygenation of 2-Methoxyphenol over Ni/Kieselguhr Catalysts as a Model Reaction for Bio-oil Upgrading

Ni/kieselguhr catalysts were applied to hydrodeoxygenate 2-methoxyphenol as a model reaction for bio-oil upgrading in a batch reactor at 100°C and 1.36 MPa. The Ni(40 wt%)-MgO(1.8 wt%)/kieselguhr showed much higher activity in the 2-methoxyphenol hydrodeoxygenation, which could be attributed to the optimal nickel particle size, surface area, and reducibility of the catalyst. Of the Na2CO3 + Urea, NaHCO3, and (NH4)2CO3 precipitants, the Na2CO3 + Urea showed the highest activity because the dispersion and surface area of nickel, rather than the pore size of the catalyst, seems to play an important role in the 2-methoxyphenol hydrodeoxygenation.

Development of Metallic Nickel Nanoparticle Catalyst for the Decomposition of Methane into Hydrogen and Carbon Nanofibers

Metallic nickel nanoparticles were prepared primarily as catalysts for the thermal decomposition of methane to produce hydrogen. Nickel particle aggregates with controlled crystalline size and primary particle size were prepared first by the precipitation of nickel nitrate and oxalic acid in ethanol solution, followed by the thermal decomposition of nickel oxalate dihydrate under an oxygen-free atmosphere. The concentration of the reactants was found to play a critical role in the morphology and crystalline size of the nickel oxalate dihydrate and subsequently the resulting metallic nickel catalyst. The nickel oxalate dihydrate showed different crystalline sizes and morphologies including nanosheets, nanorods, and nanoneedles, depending on the concentration of the reactants. A series of decomposition atmospheres (CH4–N2 in different ratios) were used to investigate their effects on the morphology and crystalline size of the metallic nickel particles. The addition of CH4 in the gas stream during the nickel...

On the Predictions of Carbon Deposition on the Nickel Anode of a SOFC and Its Impact on Open-Circuit Conditions

Previous thermodynamic analyses of carbon formation in SOFCs assumed that graphite could be used to represent the properties of carbon formed in the anode. It is generally observed, however, that catalytically grown carbon nanofibers (CNF) are more likely to form in the SOFC anode with nickel catalysts. The energetic and entropic properties of CNF are different from those of graphite. We compare equilibrium results based on thermochemical properties for graphite, to new results based on a previously reported value of an empirically determined Gibbs free energy for carbon fibers grown on a nickel support (with fitted values of H°CNF = 54.46 kJ/mol and S°CNF = 68.90 J/mol/K for a nickel crystal size of 5.4 nm). There is little difference in predictions of carbon formation under open-circuit conditions between the two carbon types for methane mixtures, with graphite predicted to form at lower temperatures than CNF. There is a much bigger difference in predictions for methanol mixtures, especially at low steam-carbon ratios. The differences for propane are even more pronounced, and the improved predictions assuming CNF are in closer agreement with past observations. We show a strong dependence of CNF formation and “coking threshold” on nickel crystallite size, supporting previous reports that the nickel particle size is a dominating parameter for controlling filament growth. If both carbon types are included in the calculations, only the thermodynamically favored form (i.e., the type having the lowest formation energy) exists. Predicted Nernst potentials are more-or-less independent of the carbon type and in agreement with measured open-circuit voltages.

Particle size effect in the low temperature reforming of methane by carbon dioxide on silica-supported Ni nanoparticles

The influence of nickel particle size in the range of 1.6–7.3nm on catalyst performance in low temperature CO2 reforming of methane reaction has been investigated using well-defined catalysts based on a neutral silica support. XAS and XPS studies indicated a reduction degree greater than 90%. The intrinsic Ni/SiO2 performances were found to be independent of nickel particle size in dry reforming at 773K using a CH4/CO2 ratio of 1.3 at 1atm, both at an early stage and in steady state conditions. The H2/CO ratio was also found to be structure in sensitive but is controlled by thermodynamics through the faster reverse water gas shift reaction.

Nickel Particle Size Effects on Cyclohexane Dehydrogenation: A Combined Reaction Kinetics and Surface Science Study

The kinetics of cyclohexane dehydrogenation was studied under near atmospheric pressure (25 Torr) at 600 K on Ni/SiO2/Mo(110) model catalysts prepared under ultrahigh vacuum conditions. The supported Ni model catalysts were characterized by Auger electron spectroscopy, temperature programmed desorption (TPD) and polarization modulation infrared reflection absorption spectroscopy (PM-IRAS). The average Ni particle sizes and particle size distributions were acquired by scanning tunneling microscopy. The kinetics results show that, for Ni particles below 2.5 nm in diameter, the specific rates (turnover frequency of benzene or TOF) increase with a decrease in particle sizes, while for Ni particles larger than 2.5 nm, the TOF is particle size independent. H2- and CO-TPD experiments as well as CO PM-IRAS spectroscopy confirm the change of Ni particles’ surface structures as a function of particle size. The particle size effect on reaction kinetics is explained by the sharp increase in the fraction of low coordinated Ni atoms on the surface of particles below 2.5 nm in diameter.

The influence of partial substitution of alkaline earth with La in the LaNiO3 perovskite catalyst

Abstract For enhancing the operation and increasing the activity of LaNiO3 catalyst in the reaction of dry reforming of methane, La was partially substituted by alkaline earth elements. The most effect was related to Ba with concentration of 0.1 (La0.9Ba0.1NiO3). XRD results showed that by adding alkaline earth the size of nickel particles is decreasing. Also, this test shows that adding Ba to the LaNiO3catalyst leading to the formation of La2NiO4 phase. There is a possibility that this phase plays a fundamental role in increasing the activity of the catalyst.

Nickel supported carbon nanofibers as an active and selective catalyst for the gas-phase hydrogenation of 2-tert-butylphenol

Nickel supported fishbone carbon nanofibers (CNFs) have been prepared by vacuum impregnation (VI) and homogeneous deposition–precipitation (HDP) methods with different nickel loadings (ca. 5%, 9% and 12%) with the aim to study the influence of the metal incorporation method and the nickel loading in the catalytic activity of gas-phase hydrogenation of 2-tert-butylphenol (2-TBP). Moreover, the influence of the nature of the support was also studied by preparing nickel catalysts supported on other carbon (active carbon (AC) and graphite (G)) and non-carbonaceous materials (alumina (AL) and yttria-stabilized zirconia (YSZ)). Different techniques were employed to characterize both the supports and the final Ni catalysts: atomic absorption spectrometry, N2 adsorption–desorption analysis, temperature-programed reduction (TPR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Catalytic results revealed that the nickel particle size and support properties affected directly to both the catalytic activity of hydrogenation of 2-TBP, and the rate of secondary reactions such as cis to trans isomerization and 2-tert-butylcyclohexanone (2-TBCN) hydrogenation.

Structured Catalysts Prepared by Electroless Plating Technique onto a Metal Substrate, for a Wall-Type Hydrogen Production System

This article reviews our works on the structured catalysts for a wall-type hydrogen production system including methanol steam reforming (MSR), CO shift reaction (CO SR) and methanol decomposition (MD). The structured catalysts were copper-based, palladium-based and nickel-based catalysts. Such a series of structured catalysts were prepared by the electroless plating technique that is a novel method for preparing a structured type catalyst onto a metal-substrate. The copper-based catalyst exhibited high performance for MSR and CO SR, the palladium-based catalyst high for MSR, and the nickel-based catalyst high for MD. The catalytic properties of these catalysts were affected by the difference of the plating condition and the pretreatment condition prior to the reaction. In the copper-based catalyst, the reforming and shift activities were enhanced by the oxidation treatment. One of the factors of such activity enhancement by the oxidation was thought to be in close proximity existence of copper and zinc atoms. A lot of monodentate-type formate species having high reactivity was formed on the oxidized catalyst, which would be correlated to the activity enhancement. In the palladium-based catalyst, the reforming activity was improved by the continuous reduction treatment followed by the oxidation. Such continuous pretreatment formed the PdZn alloy species thought to be a reforming site in the surface layer. The decomposition performance of the nickel-based catalyst depended on the ratio of the crystallite size of nickel particles to that of aluminum particles. The electronic influence of zinc and phosphorous components incorporated in the plated layer contributed to the improvement of the selectivity of product.

Steam reforming of acetic acid over Ni/ZrO2 catalysts: Effects of nickel loading and particle size on product distribution and coke formation

Steam reforming of acetic acid has been carried out over a series of Ni/ZrO2 catalysts to measure the effects of nickel loading on distribution of the reforming products and coke formation. Ni (≤13wt.%)/ZrO2 catalysts do not contain enough active metal sites for steam reforming of both acetic acid and organic by-products. Ni (≥20wt.%)/ZrO2 catalysts can effectively catalyze steam reforming but lack selectivity, since methanation and reverse water gas shift reactions are promoted, leading to low hydrogen yields. Ni (16wt.%)/ZrO2 catalyst is the most selective one, due to its low activity to the secondary reactions that contribute to by-product production. Coke formation is suppressed with the increase of nickel loading up to 16wt.%, and then restarts to increases with the further increase of nickel loading. Polymerization of acetone is the main route for coke deposition over the Ni (≤13wt.%)/ZrO2 catalysts. Methane decomposition and CO disproportion are the two main routes for coke formation over the Ni (≥20wt.%)/ZrO2 catalysts, and methane contributes more to coke formation than CO. In addition, activity of Ni/ZrO2 catalyst towards the secondary reactions such as methanation, reverse water gas shift reaction, methane decomposition, and CO disproportion are closely related to nickel loading and nickel particle sizes.