Nickel Particle Size Research Articles

Steam Prereforming of Natural Gas over Nanostructured Nickel/Magnesium Aluminate Spinel Catalysts: Effect of Support and Nickel Loading

AbstractMesoporous MgAl2O4 powder with a high surface area (226 m2 g−1) is synthesized by a co‐precipitation method in the presence of a capping agent. The obtained powder was employed to prepare catalysts (y Ni/MA) with different nickel contents (y=3.5, 7, 10.5, and 14 wt %). The catalysts were characterized by BET, XRD, H2‐TPR, TPD, TPO, and SEM techniques to study the effect of support and nickel content on the surface properties, Ni–MgAl2O4 interactions, Ni2+ species, nickel particle size, and reducibility. The catalytic performance of the y Ni/MgAl2O4 catalysts was tested in the steam prereforming of natural gas in the range of 400–550 °C, atmospheric pressure, low steam to carbon molar ratio (S/C=1.5) and a high gas hourly space velocity (GHSV=1×105 mL g−1catalyst h−1). The 10.5 % Ni/MA catalyst showed the highest nickel metal area (2.91 m2 g−1catalyst) which resulted in around 100 % of ethane and propane conversions at temperatures higher than 500 °C. This catalyst exhibited a high stability during 50 h time on‐stream, implying a high resistance to coke formation. While the 10.5 % Ni/MAC catalyst, the support (MAC) of which was synthesized by the solid‐state reaction method, demonstrated the lowest nickel area (0.04 m2 g−1catalyst) and a poor catalytic performance with a plenty of carbon deposition during steam prereforming reaction.

Catalytic reforming of toluene and naphthalene (model tar) by char supported nickel catalyst

The purpose of this study was to utilize gasification derived char as a catalyst support for tar removal. Red cedar char collected from downdraft bed gasification was chemically activated into activated carbon and impregnated with nickel acetate and nickel nitrate. The effects of nickel salts precursor, nitric acid treatment of support and reduction of nickel in hydrazine medium on catalyst performance were studied. It was found nickel nitrate was a better nickel precursor than nickel acetate for preparation of char supported nickel catalyst. The catalyst impregnated with nickel nitrate was found more active in steam reforming of toluene than the catalyst impregnated with nickel acetate. TEM results indicated that nickel particle size of the catalyst impregnated with nickel nitrate was much smaller than that of the catalyst impregnated with nickel acetate. Toluene showed higher removal efficiency than naphthalene. The presence of naphthalene decreased the toluene removal.

Hydrogen production by steam reforming of ethanol over Ni-Sr-Al2O3-ZrO2 aerogel catalyst

Ni-Sr-Al2O3-ZrO2 aerogel (NSAZ-Ae) catalyst was prepared by an one-step epoxide-driven sol-gel method and a subsequent supercritical CO2 drying method. For comparison, Ni-Sr-Al2O3-ZrO2 xerogel (NSAZ-Xe) catalyst was also prepared by a sol-gel method and a subsequent conventional evaporative drying method. NSAZ-Ae catalyst retained higher surface area and larger pore volume than NSAZ-Xe catalyst. NSAZ-Ae catalyst also showed strong interaction between active metal and support, which led to small nickel particles after the reduction. H2-TPD (temperature-programmed desorption) results revealed that NSAZ-Ae catalyst with smaller nickel particle size had higher nickel dispersion and higher nickel surface area. In addition, NSAZ-Ae catalyst showed higher ethanol adsorption capacity than NSAZ-Xe catalyst. Performance and stability of the catalyst in the ethanol steam reforming reaction was enhanced with the employment of supercritical drying as observed for NSAZ-Ae catalyst. Enhanced physicochemical property and high nickel surface area (high nickel dispersion) of NSAZ-Ae catalyst led to excellent catalytic activity and stability in the hydrogen production by steam reforming of ethanol.

Durablility of Methane Steam Reforming Catalysts Prepared By Exsolution and Infiltration

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.

Ex-Situ 3D Nano-Ptychography of Ni-YSZ SOFC Anode during Redox Cycling

Solid oxide cells (SOC) are used for efficient and cost-effective conversion of a wide variety of fuels (SOFC) for power generation or for energy storage via electrolysis (SOEC). However, SOC lifetime under harsh operating conditions is limited by electrode microstructure durability. In particular, the state of the art anode electrodes are composed of a porous cermet of nickel and yttria stabilized zirconia (YSZ). Electrochemical reactions occur where the ion and electron conducting phases meet the pores at the triple phase boundaries (TPB). Thus, the electrochemical activity of the electrode is strongly dependent on the density of TPBs and the quality of the connecting pathways through each phase1. Despite nickel remaining stable under reducing environments, nickel oxidation can occur in the electrode due to air leakage in the fuel system or by mechanical failure of the electrolyte. During operation, redox cycles can impact the lifetime of the electrode thus tracking their effect on the microstructure in 3D provides valuable information. 3D characterization of a Ni-YSZ electrode was first achieved in 20062 using focused ion beam scanning electron microscope (FIB-SEM) nanotomography and it has been routinely performed for the last decade followed by the development of near edge X-ray nano-tomography3 and most recently holotomography4. Near edge X-ray nano-tomography and FIB-SEM has been used to study the effects of oxidation on Ni-YSZ electrodes3 X-ray Ptychography is a scanning based technique in which a set of several local far-field scattering patterns is obtained by scanning the sample with a coherent micrometer-size X-ray beam. When used in tomography mode, ptychography provides a quantitative measurement of the local electron density of materials in 3D. Over the years, ptychography has demonstrated high sensitivity to mass density changes and the highest resolution among the X-ray imaging techniques5. As a proof of concept, we report the first results of ptycho-nanotomography applied to an “ex-situ” redox experiment performed at the cSAXS beamline at the Swiss Light Source (PSI). In the experiment the same Ni-YSZ anode microstructure is first analyzed in its pristine state, then oxidized and finally reduced again at 850°C in air and in 4%H2-96%N2 respectively. A specimen containing both Ni-YSZ electrode and YSZ electrolyte was created using a high precision mechanical polishing procedure followed by FIB ion milling. The “ex-situ” treatments were carried out in a small custom made tube furnace between each ptychography scan at the beamline. Datasets typically 20x20x12 µm in size were quantified to have a 3D spatial resolution of 55 nm using the Fourier shell correlation method5. The high mass density sensitivity of ptychography, resulted in high phase contrast between Ni, YSZ, NiO and pore, enabled us to effectively resolve all the phases present in the electrode (figure 1a,b,c). Therefore, an accurate segmentation procedure could be applied minimizing the associated geometrical errors of calculated microstructural parameters. Here we describe the major microstructural changes which can be noticed in the microstructure showing the evolution of the nickel particle size distribution, connectivity and tortuosity in this recent experiment. Moreover, the morphological changes in the YSZ phase are also discussed with emphasis on the observed micro-cracks (figure 1d) and their effect on the overall connectivity.

Catalytic performance of mesoporous MgO supported Ni catalyst in steam reforming of model compounds of biomass fermentation for hydrogen production

Steam reforming (SR) of pure butanol and a specific mixture (butanol/acetone/ethanol = 6/3/1, mass ratio) assumed as a model of bio-butanol raw mixture have been researched over mesoporous MgO supported Ni catalysts with various particle size (3.6–8.8 nm). The catalysts were characterized by N2 adsorption, H2-TPR, XRD, XPS and TEM. The volcano-like curves were observed when the H2 yield and H2 selectivity were plotted as a function of the nickel particle size in butanol steam reforming (BSR) and acetone–butanol–ethanol steam reforming (ABESR) reactions. Prepared mesoporous Ni0.12/MgO catalysts exhibited the highest catalytic performance in two model reaction systems. Surprisingly, the Ni particle size effects in BSR developed difference with counterpart in ABESR. Specifically, the catalytic performance of mesoporous Ni0.20/MgO even outperform that of mesoporous Ni0.08/MgO catalyst with respect to lower by-products selectivity and higher hydrogen yield in ABESR compared to BSR results.

Effect of support on hydrogen production from chemical looping steam reforming of ethanol over Ni-based oxygen carriers

The Ni-based oxygen carriers (OCs) with different supports including alloy Ni/Al2O3, lamellar Ni/MMT, mesoporous Ni/Al-MCM-41 and mesoporous Ni/SBA-15 were synthesized. The effect of support on hydrogen production from chemical looping steam reforming (CLSR) of ethanol was investigated in a fixed-bed reactor. The oxygen carriers were characterized by some techniques, including N2 adsorption–desorption, XRD, TEM, ICP-OES, H2 pulse chemisorption, H2-TPR, and TG-DTG. It was observed that Ni/SBA-15 exhibited most efficient confinement effect followed by Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3 via: 1) small nickel particle size and high dispersion as well as strengthened metal-support interaction; 2) sintering resistance due to spatial restriction of support; 3) anti-coke capability derived from small nickel particles and ordered diffusion routes for reactants and products. In addition, the silica supported OCs were conductive to promote water gas shift (WGS) reaction but the supports containing Al atoms were prone to coke deposition due to the formation of acid sites. The ‘dead time’ and oxygen transfer capacity reflected that the redox performance of oxygen carriers was listed in the following order: Ni/SBA-15, Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3. Ni/Al-MCM-41 exhibited excellent activity in initial cycle of CLSR but the collapse of the Ni/Al-MCM-41 structure for its weak thermo stability leaded to the deactivation and sintering of active phase. The Ni/SBA-15 and lamellar Ni/MMT OCs exhibited superior activity and stability but the performance of Ni/Al2O3 OCs was mediocre.

Liquid phase hydrogenation of adiponitrile over acid-activated sepiolite supported K–La–Ni trimetallic catalysts

Acid-activated sepiolite (ASEP) supported K–La–Ni trimetallic catalysts were prepared and tested in the liquid phase hydrogenation of adiponitrile (ADN). The sepiolite was treated with dilute hydrochloric acid solution to obtain ASEP, ASEP supported K–La–Ni trimetallic catalysts were prepared by the incipient impregnation method and characterized by nitrogen adsorption–desorption, temperature programmed reduction, hydrogen chemisorption, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and energy dispersive X-ray. It was revealed that potassium could inhibit the formation of the 1-azacycloheptane by-product by neutralizing some acid sites on the catalyst, and the potassium and lanthanum could efficiently reduce nickel particles size and improve its dispersion. Sepiolite treated with hydrochloric acid increases the number of silanol groups (Si–OH) on the sepiolite surface, which is helpful to nickel particles adsorption and dispersion. ASEP supported K–La–Ni trimetallic catalysts (K–La–Ni/ASEP) present better catalytic performance under mild reaction conditions of 373 K and 2.0 MPa, the ADN conversion reaches to 90.03 %, the selectivity to 6-aminocapronitrile and hexamethylenediamine is up to 90.22 %.

Effect of Nickel Particle Size on Eactive Sintering Production of Niti Shape Memory Alloy

Effect of Nickel Particle Size on Eactive Sintering Production of Niti Shape Memory Alloy

Effect of alumina percentage on size and superparamagnetic properties of Ni-Al2O3 nanocomposite synthesized by solution combustion

This paper investigates a method to achieve a close to superparamagnetic behavior in Ni-Al2O3 nanocomposite synthesized by solution combustion. The starting materials used are nickel and aluminum nitrates, as oxidizers, and urea, as fuel. Samples with 3, 10, 15, 25, 35 and 45wt.% alumina are produced on a hot plate at 330°C in air. The results show that the change in the content of Al2O3 can change the size of nickel crystallites and particles. The nickel particle size decreased by increasing the alumina content (from about 644nm to 38nm) and resulted in linear hysteresis loops and a relatively high magnetic saturation. The smallest mean nickel particle size measured using TEM images was larger than the critical size that indicates a typical superparamagnetic behavior. The observed linear hysteresis loops and the close to superparamagnetic behavior observed in the nanocomposite are mainly attributed to the combination of two different magnetic behaviors of ferromagnetic nickel and diamagnetic alumina.

Nickel-based catalyst derived from NiO–Ce0.75Zr0.25O2 nanocrystalline composite: Effect of the synthetic route on the partial oxidation of methane

In this work, we investigated the effects of two different synthetic routes, Pechini and microwave-induced combustion method, on the properties of nickel-based catalysts derived from NiO-Ce0.75Zr0.25O2 nanocomposite. Powder samples were characterized by specific surface area (SSA) via BET method, X-ray diffraction (XRD), scanning electron microscopy (SEM) and temperature-programmed reduction (TPR). It was found that the synthesis method has a significant influence on the powder morphology, which may affect the catalytic activity. The nickel-based catalysts were tested for the partial oxidation of methane showing high CH4 conversion, 80% and 81% after the first hour on stream, for the samples prepared by Pechini and combustion method, respectively. These samples also exhibited catalytic stability, keeping CH4 conversion levels about 77% and 80% after ten hours on stream, respectively. We suggest that such good performance is related to the good dispersion and particle size of the metallic nickel over Zr-CeO2 support.

Low-temperature catalytic steam reforming of toluene over activated carbon supported nickel catalysts

In order to decrease the reaction temperature of catalytic cracking of tar derived from biomass gasification and prolong the lifetime of catalyst, nickel supported on activated carbon (Ni/AC) catalysts were prepared by impregnation method and used in steam reforming of toluene, a model tar compound, in a fixed bed reactor. The physiochemical properties of the catalysts were analyzed by N2 adsorption, X-ray diffraction (XRD), and transmission electron microscopy (TEM), etc. The effects of nickel content, calcination temperature and reaction temperature on carbon conversion were investigated, and the catalytic performance of the Ni/AC catalyst was compared with those of Al2O3/olivine-supported nickel catalysts. The results showed that the Ni/AC catalyst with 10 wt% of nickel loading and 600°C of calcination temperature had the best low-temperature catalytic activity at 600°C for toluene reforming, and the carbon conversion achieved about 99%. The high performance of the 600-10%Ni/AC catalyst was probably accounted for the AC support, which had a large BET surface area and unique porous structure, and therefore, a fine nickel particle size distribution on it. It also could be known by XRD analysis that nickel loaded on the surface of AC was in the form of metallic state after calcination, thus decreasing the use of hydrogen for reduction before reaction, so the catalyst preparation process can be simplified and the cost will be saved.

Nickel catalyst with outstanding activity in the DRM reaction prepared by high temperature calcination treatment

The catalytic performance of some NiCe/Al2O3 catalytic systems (11 wt.% Ni and 3 wt.% Ce) were checked after being submitted to different calcination and reduction treatments. It was found that, the reduced NiCe/Al2O3 catalysts were more active and stable in the dry reforming reaction of methane than the corresponding not-reduced catalysts. This high activity was initially connected with the smaller size of pre-reduced Ni species, which at the same time leads on to the formation of filamentous carbon. The best overall performance was obtained for the reduced catalyst after being calcined at 1000 °C. This catalyst presents a very high stability, a low level of carbon formation, maintaining the nickel particle size constant during reaction. Surprisingly, although its reduction degree is only 12% at 750 °C, its catalytic activity is similar to the full reduced catalysts. So, the small number of reduced metallic particles of this catalyst shows a very high activity, much higher than the other catalysts.

The combustion synthesis of Ni–Ti intermetallic compounds

Combustion synthesis is a novel method which has been successfully used for the production of numerous refractory compounds. In the present study, this process was used to synthesise porous Ni–Ti intermetallic compounds. Two different nickel particle sizes (10 and 63 μm) were used to make compacts with different Ni + Ti:Ti + C ratios of 100:0, 90:10 and 80:20. The use of fine nickel particle size resulted in an intense reaction and the products were deformed as a result of melting. In the samples with larger nickel particle size, melting did not occur and the products only underwent an expansion because of an increase in the pore fraction. The reaction between Ti and C increased the exothermicity of the total process, and yielded products with a better distribution of pores. The products were characterised by SEM and XRD analyses. The main phases detected in the products were NiTi and NiTi2. TiC particles were also dispersed within the matrix.

Uniform Ni particles on amino-functionalized SBA-16 with excellent activity and stability for syngas methanation

Via modification of mesoporous material SBA-16 with silane coupling agent, a new functionalized SBA-16 catalyst immobilized Ni has been prepared. The performance of the catalyst for CO methanation then were systemically investigated in a continuous flow fixed-bed reactor. The as-synthesized catalyst was characterized with N2 absorption-desorption, X-ray diffraction, Transmission electron microscopy (TEM), FT-IR spectrum, 29Si-nuclear magnetic resonance (NMR), H2—Temperature Programmed Reduction (TPR) and H2 pulse chemisorption. After modification by aminopropyl-trimethoxysilane (APTMS), the internal surface silanol group of support SBA-16 was replaced by amino-groups. The replacement of hydroxyl groups by amino groups could prevent the agglomeration of metal ion in the solution. Also uniform nickel particle size was observed because the replaced organic groups on SBA-16 could form homogeneous interaction towards the metal. Comparing with the catalyst without functionalized, the catalyst Ni/SBA-16-NH2 exhibited higher activity, excellent heat-resistant performance and better stability in CO methanation. The CO conversion and CH4 selectivity could be 100% and 99.9% at the optimal temperature. Meanwhile, the catalyst showed no decrease of activity in the 100h life test.

Transport of sulfur in prereforming catalyst during steaming conditions

Industrial start-up, operation, and shutdown conditions of a prereformer catalyst can vary, and the present work has the objective to study the consequence of start-up and shutdown conditions on the sulfur chemisorbed on the nickel surfaces in the catalytic bed. These are conditions where the catalyst is being fed with steam without the presence of hydrogen or a reductive species producing hydrogen. The experimental tests were performed in a pilot unit using aged and presulfided catalyst for the upper part of the catalyst bed and aged but sulfur-free catalyst in the lower part.The results of the experiments showed that, regardless of the support type (alumina, including calcium-carbonate-doped alumina, alumina-magnesia spinel, or calcium aluminate), the sulfur will be released from the nickel surface and transported downstream in the catalyst bed. Although this leads to a re-activation of the catalyst in the upper part of the catalyst bed due to the desorption of sulfur, the overall activity will drop due to the more significant deactivation of the downstream catalyst. The transportation of the sulfur is accompanied by nickel particle sintering, resulting in larger nickel particle sizes in the part of the bed where sulfur has been present consequently reducing the catalyst activity further. The rate of the sulfur transport is highly temperature dependent in the tested temperature interval from 350°C to 550°C, having minor transport at low temperature, but significant transport of sulfur at the higher temperatures.The experimental investigations have been further verified by industrial observation, where a high steam-to-hydrogen ratio in prereformers during operation has led to prereformer re-activation in the upper part and observed sulfur poisoning of catalysts downstream the prereformer.

Effect of Particle Size of Titanium and Nickel on the Synthesis of NiTi by TE-SHS

In this work, the influence of the particle size of nickel and titanium on the synthesis of NiTi shape memory alloy by self-propagating high-temperature synthesis (SHS) was investigated. It was found that coarse titanium and nickel powders undergo only a limited SHS reaction. On the other hand, too fine powders support the low-temperature diffusional formation of NiTi intermetallics at 773 K to 1073 K (500 °C to 800 °C) which could then suppress the SHS reaction. The optimum powder fraction of both nickel and titanium to achieve the most intensive SHS reaction is 25 to 45 µm. The influence of the particle size of both nickel and titanium on the reaction mechanism is discussed in terms of the microstructure evolution, phase, and chemical composition changes and thermal effects determined by differential thermal analysis.

Effect of initial nickel particle size on stability of nickel catalysts for aqueous phase reforming

The deactivation behavior by crystallite growth of nickel nanoparticles on various supports (carbon nanofibers, zirconia, SiC, α-Al2O3 and γ-Al2O3) was investigated in the aqueous phase reforming of ethylene glycol. Supported Ni catalysts of ∼10wt% were prepared by impregnation of carbon nanofibers (CNF), ZrO2, SiC, γ-Al2O3 and α-Al2O3. The extent of the Ni nanoparticle growth on various support materials follows the order CNF∼ZrO2>SiC>γ-Al2O3>>α-Al2O3 which sequence, however, was determined by the initial Ni particle size. Based on the observed nickel leaching and the specific growth characteristics; the particle size distribution and the effect of loading on the growth rate, Ostwald ripening is suggested to be the main mechanism contributing to nickel particle growth. Remarkably, initially smaller Ni particles (∼12nm) supported on α-Al2O3 were found to outgrow Ni particles with initially larger size (∼20nm). It is put forward that the higher susceptibility with respect to oxidation of the smaller Ni nanoparticles and differences in initial particle size distribution are responsible for this behavior.

Highly loaded Ni-based catalysts for low temperature ethanol steam reforming.

This paper describes the design of high-loading Ni/Al2O3 catalysts (78 wt% Ni) for low temperature ethanol steam reforming. The catalysts were synthesized via both co-precipitation (COP) and impregnation (IMP) methods. All the catalysts were measured by N2 adsorption-desorption, XRD, H2-TPR, and H2 pulse chemisorption. The characterization results demonstrated that the preparation method and the loading significantly affected the nickel particle size, active nickel surface area and catalytic performance. Over COP catalysts, large nickel particles were presented in nickel aluminum mixed oxides. In comparison, IMP catalysts gained more "free" NiO particles with weak interaction with the aluminum oxide. Consequently, COP catalysts yielded smaller nickel particles and larger active nickel surface areas than those of IMP catalysts. High loading is beneficial for obtaining sufficient active nickel sites when nickel particles are dispersed via COP, whereas excessive nickel content is not desired for catalysts prepared by IMP. Specifically, the 78 wt% nickel loaded catalyst synthesized by COP possessed small nickel particles (∼6.0 nm) and an abundant active nickel area (35.1 m(2) gcat(-1)). Consequently, COP-78 achieved superior stability with 92% ethanol conversion and ∼35% H2 selectivity at 673 K for 30 h despite the presence of a considerable amount of coke.

Structural and mechanical properties of graded composite Al2O3/Ni obtained from slurry of different solid content

In this work, an alumina-nickel graded hollow cylinders were prepared by the centrifugal slip casting. In the paper, the results for samples formed from slurries with different solid content: 45 vol.%, 40 vol.% and 35 vol.% are presented. The structure of the samples after sintering was examined by X-ray diffraction (XRD). The microstructure of the composite, especially the nickel particle size distributions were investigated by using scanning electron microscopy (SEM). An image analyzer has been used for the measurement of volume fraction of the nickel particles in the composites. The hardness was measured by using a Vickers hardness-testing. Based on hardness measurements KIC value were determined. The XRD results confirmed only two phases: Ni and α-Al2O3 in all samples. The preliminary macroscopic observation as well as SEM showed, that the microstructure of the sample cross-section is not homogeneous. Microstructural characterization revealed the gradation of nickel content along the radial direction of hollow cylinder. Three zones were distinguished, from outer surface towards the inner side of the tube. The maximum of volume fraction of nickel particles was obtained at the middle zone of the composites. The results of hardness-testing revealed that the maximum hardness values were observed in region at the inner edge of the casting due to an absence of nickel particles.