Nickel Crystallites Research Articles

Ni-Mg-Al Hydrotalcite-Derived Catalysts for Ammonia Decomposition—From Precursor to Effective Catalyst

A series of Ni-Mg-Al hydrotalcite-derived mixed metal oxides with different Ni/Mg ratios were prepared by the coprecipitation method followed by calcination at 600 °C. The hydrotalcite-like materials, as well as their calcined forms, were characterized with respect to structure (XRD, UV-Vis DRS), chemical composition (ICP-OES), textural parameters (low-temperature N2 sorption), dispersion of nickel species (H2-chemisorption) and nickel species reducibility (H2-TPR). Moreover, the process of hydrotalcite-like materials’ thermal transformation to mixed metal oxide systems in air and argon flow was studied by the TG-DTA method. The activity of the studied catalysts in the reaction of ammonia decomposition increased with an increase in nickel content in the samples. It was shown that nickel species incorporated into the Mg-Al oxide matrix segregated under conditions of reduction in a flow of H2/Ar mixture with the formation of metallic nickel crystallites of the average size of about 10 nm. The size of nickel crystallites was practically no change in the subsequent reduction cycles and resulted in increased catalytic activity in comparison to larger crystallites of metallic nickel (20.2–23.6 nm) deposited on Al2O3 and MgO.

Does the active surface area determine the activity of silica supported nickel catalysts in CO2 methanation reaction?

Does the active surface area determine the activity of silica supported nickel catalysts in CO2 methanation reaction?

Tailoring structural and magnetic properties of NiCu nanowires by electrodeposition

Tailoring structural and magnetic properties of NiCu nanowires by electrodeposition

Fabrication and Characterization of Thin Metal Films Deposited by Electroless Plating with Organic Additives for Electrical Circuits Applications.

In our work, we studied thin nickel films deposited by electroless plating for use as a barrier and seed layer in the through-silicon vias (TSV) technology. El-Ni coatings were deposited on a copper substrate from the original electrolyte and with the use of various concentrations of organic additives in the composition of the electrolyte. The surface morphology, crystal state, and phase composition of the deposited coatings were studied by SEM, AFM, and XRD methods. The El-Ni coating deposited without the use of an organic additive has an irregular topography with rare phenocrysts of globular formations of hemispherical shape and a root mean square roughness value of 13.62 nm. The phosphorus concentration in the coating is 9.78 wt.%. According to the results of the X-ray diffraction studies of El-Ni, the coating deposited without the use of an organic additive has a nanocrystalline structure with an average nickel crystallite size of 2.76 nm. The influence of the organic additive is seen in the smoothening of the samples surface. The root mean square roughness values of the El-Ni sample coatings vary within 2.09-2.70 nm. According to microanalysis data the phosphorus concentration in the developed coatings is ~4.7-6.2 wt.%. The study of the crystalline state of the deposited coatings by X-ray diffraction made it possible to detect two arrays of nanocrystallites in their structure, with average sizes of 4.8-10.3 nm and 1.3-2.6 nm.

Neodymium promoted ceria and alumina supported nickel catalysts for CO2 methanation reaction

Two series of catalysts containing 20 wt.% nickel, promoted with different amounts of neodymium from 1 to 10 wt.% were prepared by the impregnation method, using nano-CeO2 and γ-Al2O3 as supports. Ceria supported nickel catalysts showed high activity in CO2 methanation reaction and weak activity changes were observed with an increase in Nd content. X-ray diffraction, hydrogen chemisorption and transmission electron microscopy studies evidenced a decrease in the average size of nickel crystallites and an increase in the active surface area of catalysts. The temperature-programmed reduction, oxidation and CO2 desorption, XPS, Raman and in-situ FTIR spectroscopy indicated complex changes in the nature of their redox and base centres. Non-promoted alumina supported nickel catalyst despite higher surface area showed lower activity than similar catalyst with ceria as support. However, an introduction of Nd-promoter led to strong increase in their activity. Such effect was mainly ascribed to the increase in their basicity, facilitation of CO2 activation and subsequent transformation of the intermediate surface species to methane with participation of hydrogen atoms activated on metallic nickel crystallites.

Ni-Mg/Al Mixed Oxides Prepared from Layered Double Hydroxides as Catalysts for the Conversion of Furfural to Tetrahydrofurfuryl Alcohol

Ni-Mg/Al mixed oxide catalysts (Ni2Al, Ni2Mg1Al, and Ni1Mg1Al) obtained from layered double hydroxides (LDHs) were tested on the one-pot production of tetrahydrofurfuryl alcohol (TFA) from furfural (FF). Upon calcination at 400 °C and reduction at 500 °C, the LDHs gave catalysts containing small nickel crystallites (<4 nm) dispersed on mixtures of metal oxides and spinel structures. Complete conversion of FF (>99.5%) was achieved on all the catalysts after 4 h at 190 °C and 5.0 MPa of H2 using 5 wt.% FF in ethanol and a furfural-to-catalyst mass ratio of 7.44 g/g. TFA evolved from the sequential hydrogenation of FF to furfuryl alcohol (FA) to TFA. Competing reaction routes involved decarbonylation of FF to furan (FUR) followed by hydrogenation to tetrahydrofuran (THF) or hydrogenolysis to n-butane (BU) and the hydrogenation of the carbonyl group in FF to form 2-methyl furan (mFUR) and its hydrogenation to 2-methyltetrahydrofuran (mTHF). A third competing route consisted of the nucleophilic addition of FF with ethanol and with FA to form acetals (such as 2-(diethoxymethyl)furan, FDA), which were later converted to difurfuryl ether (DFE) and tetrahydrofurfuryl ethyl ether (TFEE) as final products. Hydrogen pressure favored the production of TFA and diminished the formation of acetals, while temperature reduced the capacity of the catalyst to hydrogenate the furan ring, thus reducing TFA and increasing FA and FUR. An 80% yield to TFA was achieved with the Ni2Mg1Al catalysts after 6 h at 190 °C and 50 bar H2, but a variety of coproducts were present at low concentration. Testing of the catalysts in gas-phase hydrogenation conditions at atmospheric pressure revealed a poorer performance, with FA as the main product.

Nickel–magnesium-modified cenospheres for CO2 methanation

Nickel–magnesium-modified cenospheres for CO2 methanation

Self-combustion Ni and Co-based perovskites as catalyst precursors for ammonia decomposition. Effect of Ce and Mg doping

Self-combustion Ni and Co-based perovskites as catalyst precursors for ammonia decomposition. Effect of Ce and Mg doping

Electrocatalytic Ammonia Oxidation Mediated by Nickel and Copper Crystallites Decorated with Platinum Nanoparticle (PtM/G, M = Cu, Ni)

Electrocatalytic Ammonia Oxidation Mediated by Nickel and Copper Crystallites Decorated with Platinum Nanoparticle (PtM/G, M = Cu, Ni)

Synthesis gas production by dry reforming of methane over Neodymium-modified hydrotalcite-derived nickel catalysts

Synthesis gas production by dry reforming of methane over Neodymium-modified hydrotalcite-derived nickel catalysts

Effect of cobalt promotion on hydrotalcite-derived nickel catalyst for CO2 methanation

Effect of cobalt promotion on hydrotalcite-derived nickel catalyst for CO2 methanation

Studies and Research on the Influence of Deposit Parameters on the Characteristics of Composite Coatings Ni-Al2O3 Obtained by Electrochemical Methods

The paper presents the characterization of composite coatings with nickel matrix using as dispersed phases Al2O3 particles, both from the microstructural point of view and from the point of view of the layer thickness, micro-hardness and corrosion behavior in saline fog. The presence of dispersed phase particles led to the finishing of the structure because they acted as nucleus centres, reducing the size of nickel crystallites. The parameters of the deposits influence the structure and properties of the obtained layers.

The state of BEA zeolite supported nickel catalysts in CO2 methanation reaction

The state of BEA zeolite supported nickel catalysts in CO2 methanation reaction

Preparation, Properties and Applications of the Hybrid Organic/Inorganic Nanocomposite Based on Nanoporous Carbon Matrix

Nanoporous carbon matrix was prepared by the sol–gel process from pyrogallol-formaldehyde (PF) mixtures in water using picric acid as catalyst. For the second sample, nickel oxide nanoparticles were added in the PF matrix to get a PF/NiO hybrid organic/inorganic nanocomposite. After a drying step, the samples were heat treated for two hours at 650 °C in tubular furnace under open nitrogen atmosphere. The XRD analysis shows that PF matrix is amorphous while PF/NiO nanocomposite exhibited a metallic phase of nickel. The average value of the metallic nickel crystallites deduced from the Scherrer’s equation was found to be about 35 nm. TEM images indicate the existence of nanopores in the PF matrix and the presence of nickel nanoparticles in the PF/NiO nanocomposite which are dispersed randomly in the carbon matrix. The adsorption–desorption of nitrogen revealed that the pore size equal to 1.9 nm for PF matrix and 2.6 nm for PF/NiO nanocomposite. So, the adsorption capacities of carbon dioxide (CO2) and methane (CH4) show that the PF matrix has the highest adsorption at low pressures where micropores are dominant and the PF/NiO nanocomposite tends to adsorb gases better at high pressure where the presence of mesopores. The V(I) characteristics showed that the PF/NiO nanocomposite can be considered as a smart material. Indeed, the characteristic behavior can be adjusted according to the maximum applied current. Electrochemical measurements have shown that the PF/NiO nanocomposite is very promising for the detection of non-enzymatic glucose with a sensitivity of 76 µA/mM.cm−2 and a detection limit lower than 0.03 µM. The absorption spectra showed that the addition of the NiO nanoparticles increased the Urbach energy and the disorder in the PF/NiO nanocomposite.

Effect of current density and agitation modes on the structural and corrosion behavior of Ni/diamond composite coatings

Effect of current density and agitation modes on the structural and corrosion behavior of Ni/diamond composite coatings

Co/CeO2 and Ni/CeO2 catalysts for ethanol steam reforming: Effect of the cobalt/nickel dispersion on catalysts properties

Co/CeO2 and Ni/CeO2 catalysts for ethanol steam reforming: Effect of the cobalt/nickel dispersion on catalysts properties

Hydrogen production via surrogate biomass gasification using 5% Ni and low loading of lanthanum co-impregnated on fluidizable γ-alumina catalysts

Abstract Nickel on alumina support offers opportunity for gasification of biomass for hydrogen production. In a recent contribution from our research team, (González Castañeda, D. G., et al. 2019) showed that cerium or lanthanum co-impregnation at 2 wt% with nickel may have a favorable effect for biomass catalytic gasification. However, and given an observed influence of lanthanum on the formation of small Ni crystallite sizes, five Ni/γ-Al2O3 based fluidizable La promoted catalysts were studied. Nickel-alumina catalysts promotion was effected varying La in the 0.5 and 1.0 wt% range. Once impregnation precursors loaded, they were reduced at 480 °C via an activation step. Catalysts were characterized using BET, XRD, AA, TPR, TPD, H2-chemisorption, TEM-EDX and FTIR. Catalyst performance was established in a fluidized CREC Riser Simulator, using: a) glucose as surrogate biomass, b) 600 °C, c) steam/biomass (S/B) ratio of 1, d) catalyst /biomass (C/B) ratio of 3.2 and e) 20 s reaction time. Data obtained was analyzed using an ANOVA statistical data analysis package with the 5 wt% Ni and 0.5–1 wt% La and Ce on γ-Al2O3 catalysts, prepared using a pH of 1 of impregnating solution were the best yielding 0.53–0.56 hydrogen molar fractions. These catalysts also gave a 39% reduced coke, and this while compared with the coke formed on the 2% Ce – 5 wt%Ni/γ-Al2O3 (González Castañeda, D. G., et al. 2019). This promising performance was assigned to the dominant NH3-TPD medium acidity, the high catalyst specific surface (∼140 m2/g), and the good 9% metal dispersion with 9–10 nm nickel crystallites.

Electrodepositing Ni-TiN/Si<sub>3</sub>N<sub>4</sub> Composite Layer with Variation of Current Density

Composite of two phases with crystal grains of titanium nitride (TiN) and amorphous of silicon nitride (Si3N4) had shown an improvement of mechanical properties as shown by composite layer of nickel (Ni) and TiN. In this study, Ni-TiN/Si3N4 composite layer on tungsten carbide bar have been prepared by using electrodeposition to study the effect of current density on the microstructure and mechanical properties of the layer. The optimum properties of composite coating with no crack morphology and maximum hardness was shown by the sample electrodeposited at current density of about 2.5 mA/cm2. The high hardness was attributed to the nickel crystallite size refinement

Ni Supported on Natural Clays as a Catalyst for the Transformation of Levulinic Acid into γ-Valerolactone without the Addition of Molecular Hydrogen

γ-Valerolactone (GVL) is a valuable chemical that can be used as a clean additive for automotive fuels. This compound can be produced from biomass-derived compounds. Levulinic acid (LA) is a compound that can be obtained easily from biomass and it can be transformed into GVL by dehydration and hydrogenation using metallic catalysts. In this work, catalysts of Ni (a non-noble metal) supported on a series of natural and low-cost clay-materials have been tested in the transformation of LA into GVL. Catalysts were prepared by a modified wet impregnation method using oxalic acid trying to facilitate a suitable metal dispersion. The supports employed are attapulgite and two sepiolites with different surface areas. Reaction tests have been undertaken using an aqueous medium at moderate reaction temperatures of 120 and 180 °C. Three types of experiments were undertaken: (i) without H2 source, (ii) using formic acid (FA) as hydrogen source and (iii) using Zn in order to transform water in hydrogen through the reaction Zn + H2O → ZnO + H2. The best results have been obtained combining Zn (which plays a double role as a reactant for hydrogen formation and as a catalyst) and Ni/attapulgite. Yields to GVL higher than 98% have been obtained at 180 °C in the best cases. The best catalytic performance has been related to the presence of tiny Ni particles as nickel crystallites larger than 4 nm were not present in the most efficient catalysts.

PRODUCTION AND PROPERTIES OF COMPOSITE ELECTROCHEMICAL COATINGS WITH ELECTROCHEMICALLY DISPERSED GRAPHENE BASED ON NICKEL MATRIX

In this work, the effect of addition of colloidal solutions of electrochemical exfoliated graphene (EEG) to the Watts bath on the process of obtaining composite coatings based on a nickel matrix was studied. It was found that the introduction of nanoparticle additives has a significant effect on the value of cathodic overvoltage during electro reduction of Ni2+. The strongest inhibition of the cathode process takes place with the introduction of 0.2 g/l of additives investigated. Further increase in the concentration of nanoparticles in the bath reduces the effect. The inhibition of the cathodic reduction of Ni2+ is associated with the adsorption of graphene nanoparticles on the active faces of growing nickel crystallites and the blocking of the accessible surface for Ni2+ reduction. Due to the increase in cathodic polarization during the deposition of the composite coating, the crystallites of the deposited nickel decrease in size and the texture of the crystal structure of the coating changes. According to energy dispersive spectroscopy data, carbon has been included in the composite coating. The carbon content in the coating increases with increasing concentration of nanoparticles in the working electrolyte. The inclusion of negatively charged nanoparticles of electrochemically dispersed graphene in the resulting precipitate becomes possible due to adsorption of Ni2+ and recharging of graphene nanoparticles. It was found that the optimal concentration of electrochemically dispersed graphene in the working electrolyte is 0.1-0.2 g/l. At a given nanoparticle content in the working bath, the porosity and roughness of the coatings decreases. The Tafel polarization curves for composite coating samples obtained in a 0.5M NaCl solution showed that the inclusion of graphene nanoparticles in the resulting coating leads to a shift of the corrosion potential to the negative area. With an increase in the carbon content in the coating, the shift in corrosion potentials increases, and the value of corrosion currents increases. For samples of composite coatings obtained at an EEG additive concentration of 0.1 g/l, a slight improvement in the protective properties is noted, which is associated with a decrease in the porosity of the coatings.