Dispersed Nickel Particles Research Articles

Preparation of a finely dispersion nickel-based in-situ pyrolysis catalyst: Influence of lignocellulosic constituents

Metal/biochar catalysts could be synthesized via directly subjecting biomass impregnated with metal salts to pyrolysis. The properties of biochar are intricately linked to the inherent composition of the raw material, which in turn could influence the degree of metal dispersion and its catalytic impact. The poplar sawdust and its fractioned proportion was employed for the preparation of Ni-based biochar catalysts. The work mainly focuses on the impact of lignocellulosic material with diverse compositions on the dispersion of nickel particles during the calcination-pyrolysis co-process. Given that cellulose and holocellulose constituted the majority of the material, the matching catalyst support may encourage the migration of nickel species to produce substantial amounts of particles, perhaps as a result of several reactions such as dehydration and aromatization. In contrast, the utilization of sawdust as a support demonstrated a remarkable effect in dispersing nickel particles, nickel particle size and H2 uptake were 7.0nm and 19.8 μmol/g, respectively, while also displaying exceptional catalytic activity in the hydrogenation of vanillin, with the maximum conversion and 2-methoxy-4-methylphenol (MMP) yield of 99.7% and 69.0%. It has been determined that the presence of lignin in the system has a beneficial impact on the dispersion of nickel and its catalytic activity.

Hydrogenation of glucose to sorbitol by using nickel hydroxyapatite catalyst

AbstractA series of nickel hydroxyapatite catalysts were synthesized by the co‐precipitation method followed by calcination and reduction. These catalysts were employed for the aqueous phase hydrogenation of glucose to sorbitol. The Ni‐HAP catalyst with comparatively high surface area and acid‐base strength gave high sorbitol selectivity in 1 h. Ni‐HAP‐4 catalyst with moderate Ni (3.5 wt. %) content having smaller and highly dispersed nickel particles gives an excellent yield of sorbitol, 97 % in 1 h. The Ni‐HAP‐4 catalyst works well with other polar protic solvents. Different characterization techniques like XRD, TEM, SEM‐EDS, BET, NH3‐TPD, and CO2‐TPD were employed to analyze the Ni‐HAP‐4 catalyst.

A simple fabrication of mineral supported Ni-NiAl2O4 nanocomposites with a novel transition layer

In recent years, Ni-based catalysts have attracted widespread attention in many fields due to their low price and high catalytic activity. However, the low dispersion of active components has significantly restricted their large-scale application. In this work, we prepared a new type of sepiolite nanofibers loaded Ni-NiAl 2 O 4 composite by coupling the sol-gel and reduction methods, using nickel nitrate, aluminum nitrate and sepiolite nanofibers as the raw materials. To determine the optimal conditions for preparing the composite material, the effects of complexing agent, additives, sepiolite addition content, calcination temperature and time, and reduction temperature and time on the microstructure of the composite were systematically studied. With comprehensive characterizations, the optimal preparation conditions of the composite were determined. In the optimal composite, the NiAl 2 O 4 nanoparticles with a particle size of ~25 nm were uniformly dispersed on the sepiolite surface, and nickel nanoparticles with a size of 5 nm and well dispersion were rooting in the NiAl 2 O 4 particles. The NiAl 2 O 4 in the composite was acted as the nickel source and transition layer for the growth and dispersion of nickel particles, respectively. This work is expected to provide an effective strategy for the low-cost preparation of Ni-based catalysts, in which the novel transition layer can provide stable nickel particles with good dispersion. • A novel mineral supported nickel-based catalyst was prepared via a sol-gel reduction method. • Comprehensive characterizations were performed on the prepared materials. • The dispersion of NiAl 2 O 4 nanoparticles can be improved by sepiolite. • The NiAl 2 O 4 as a transition layer can provide nickel source for the subsequent reduction process.

Improved hydrodeoxygenation of lignin-derived oxygenates and biomass pyrolysis oil into hydrocarbon fuels using titania-supported nickel phosphide catalysts

Biomass pyrolysis oil is a potentially essential renewable energy source that can serve as an alternative to petroleum-based fuels and chemicals. In this study, biomass pyrolysis oil was converted into petroleum-like deoxygenated hydrocarbons via catalytic hydrodeoxygenation using a titania-supported nickel phosphide catalyst. The phosphor precursor was added to several transition metals, including nickel, cobalt, copper, and iron, supported on titania. The formation of isolated nickel phosphide particles, which were active for complete hydrodeoxygenation, was confirmed by the characterization of prepared catalysts. As a model reactant of biomass pyrolysis oil, a mixture of alkyl-methoxyphenol compounds was hydrodeoxygenated to produce completely deoxygenated compounds, generating an 87% yield of cycloalkanes at 300 °C and 4 MPa H2 for a reaction time of 2 h. The hydrodeoxygenation of biomass pyrolysis oil also generated a 37.4% yield of hydrocarbon fuels. The high hydrodeoxygenation activity can be attributed to the synergy between the hydrogenating metals and the acid sites, which can be improved by electron transfer from a slightly cationic nickel to a slightly anionic phosphor. Furthermore, the addition of phosphor improved the formation of highly dispersed nickel particles, increasing the quantity of hydrogen-adsorbing surface metals. The observations in this study indicate that the efficient conversion of lignocellulose-derivatives into chemicals and fuels can be achieved using modified non-precious transition metal catalysts.

Enhanced sensing performance of cement-based composites achieved via magnetically aligned nickel particle network

Cement-based sensors, consisting of a cementitious matrix filled with electrically conductive fillers, are one of the most promising sensing composites to monitor and track the status of structural systems continuously. This study proposes a new type of cement-based sensor with a unique anisotropic conductive chains activated by magnetically aligned nickel particles in a chain form structure. The piezoresistivity is significantly enhanced along the direction of the chain structure and the gauge factor ranges from 2491 to 3626, providing the sensors with excellent piezoresistivity and sensitivity. In the meantime, the usage of nickel particles drops significantly compared to the composites with randomly dispersed nickel particles. To explore its potential in engineering applications, the developed sensors are embedded in the compression zone of a beam structure. Three-point-bending test result shows that under same condition, the anisotropic sensors exhibits superior piezoresistive performance and higher sensitivity than the isotropic sensors.

Aligning conductive particles using magnetic field for enhanced piezoresistivity of cementitious composites

The electrical and mechanical properties of the cement-based composites with magneto-aligned nickel powder are investigated in this study. The microstructure of the conductive pattern is examined by scanning electron microscope (SEM) and X-ray computed tomography (CT) scanning. It demonstrates that with the intervention of magnetic field, the electrical resistivity drops significantly and percolation threshold of the composites reaches at a lower filler concentration. The problems of high filler usage, low flowability and strength exists in the composites with randomly dispersed nickel particles can be addressed using the proposed method. Additionally, investigation on the influence of magnetic field intensity and duration shows that by adjusting these key parameters, the piezoresistive performance of the cementitious composites can be lifted. Under the superior piezoresistivity, giant gauge factor of the cement sensors is achieved which demonstrates an ability of stress/strain monitoring with high sensitivity.

Effect of Support and Chelating Ligand on the Synthesis of Ni Catalysts with High Activity and Stability for CO2 Methanation

Carbon dioxide methanation was carried out over Ni-based catalysts on different supports and chelating ligands in microreactors. To investigate the influence of chelating ligands and supports, the Ni catalysts were prepared using different support such as CeO2, Al2O3, SiO2, and SBA-15 by a citric acid (CA)-assisted impregnation method. The properties of the developed catalysts were studied by X-ray diffraction (XRD), Transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) measurement, and the results show that the addition of CA in the impregnation solution improved the dispersion, refines the particle size, and enhanced the interaction of nickel species. The catalytic performance of the developed Ni catalysts were evaluated by CO2 methanation in microreactors in the temperature range of 275 °C–375 °C under 12.5 bar pressure. All the catalysts exhibit high CO2 conversion and extremely high selectivity to methane. However, the catalysts prepared via CA-assisted method exhibited excellent activity and stability, compared with Ni catalysts prepared by a conventional impregnation method, which could be attributed to highly dispersed nickel particles with strong metal–support interaction. The activity of CO2 methanation followed the order of Ni/CeO2-CA > Ni/SBA-15-CA > Ni/Al2O3-CA > Ni/SiO2-CA > Ni/CeO2. The Ni/CeO2 catalysts have also been prepared using different chelating ligands such as ethylene glycol (EG), sucrose (S), oxalic acid (OA) and ethylene diamine tetra acidic acid (EDTA). Among the tested catalysts prepared with different support and chelating ligands, the Ni/CeO2 catalyst prepared via CA-assisted method gave superior catalytic performance and it could attain 98.6% of CO2 conversion and 99.7% methane selectivity at 325 °C. The partial reduction of the CeO2 support generates more surface oxygen vacancies and results in a high CO2 conversion and methane selectivity compared with other catalysts. The addition of CA as promoter favored the synergistic effect of Ni and support, which led to high dispersion, controls the size, and stabilizes the Ni nanoparticles. Furthermore, the Ni/CeO2-CA catalyst yields high CO2 conversion in a time-on-stream study due to the ability of preventing the carbon deposition and sintering of Ni particles under the applied reaction conditions. However, the Ni/Al2O3-CA and Ni/SBA-15-CA catalysts showed stable performance for 100 h of time on stream.

Acquiring Clean and Highly Dispersed Nickel Particles (ca. 2.8 nm) by Growing Nickel-Based Nanosheets on Al2O3 as Efficient and Stable Catalysts for Harvesting Cyclohexane Carboxylic Acid from the Hydrogenation of Benzoic Acid

By growing nickel-based nanosheets on Al2O3, a nickel catalyst present as clean uniform nickel particles ca. 2.8 nm in size was feasibly produced from the two-dimensional (2D) nanoprecursor predispersing strategy, and investigated for the hydrogenation of benzoic acid to cyclohexane carboxylic acid. A 98% yield of cyclohexane carboxylic acid and a 15–40-fold enhanced turnover frequency (TOF) value (31.4 s–1) were achieved with the catalyst. These values were superior to those achieved (yield = 28%–40%, time of flight TOF = 0.8–2.0 s–1) for traditional catalysts with larger nickel particles (ca. 5.2–6.8 nm); interestingly, the superior activity was re-examined, because of the well-maintained size of the catalyst after continuous catalytic recycling. The kinetic measurements further illuminated that the reaction activation energy could be clearly decreased by employing smaller nickel particles, which could be responsible for the dramatic TOF enhancements. These results also suggest that the hydrogenation wi...

Carbon dioxide reforming of methane over MgO promoted Ni/CNT catalyst

Carbon dioxide reforming of methane to syngas was investigated over a series of MgO promoted Ni/CNT catalysts. MgO played a critical role in improving the catalytic performance of Ni/CNT. The results showed that the addition of MgO strengthened the interaction of Ni and interior surface of CNT. Highly dispersed nickel particles with small size (less than 4.5 nm) were also observed in MgO modified CNT. Otherwise, the NiO nanoparticles were facilely reduced over the catalyst prepared with a narrow size of CNT, as shown in H2-TPR. The reaction tests demonstrated that the Ni-based catalyst with an addition of MgO and narrow size of CNT exhibited better catalytic activity. Furthermore, the lifetime of Ni-based catalyst was prolonged effectively after adding MgO, attributed to the stabilization and dispersion of Ni particles and the effective restraint on the gasification of CNT.

Ni based catalyst supported on KIT-6 silica for CO methanation: Confinement effect of three dimensional channel on NiO and Ni particles

Several nickel catalysts supported on silica KIT-6 were synthesized via the incipient wetness impregnation method and the performance of the catalysts in CO methanation were investigated in a continuous flow fixed bed reactor. The mesoporous silica KIT-6 has three dimensional framework and large surface area, which can offer adequate sites for the metal to disperse. The amount of nickel loading has significantly affected the metal surface area and dispersion of nickel particles on the support. The catalysts with higher Ni loading exhibited better activity in CO methanation. It was also found that, compared with Al2O3, SiO2 and even meseporous SBA-15, KIT-6 silica has an obvious confinement effect to NiO particles as the size of NiO particles maintained consistent under different calcination temperature. However, at higher temperature, metallic nickel particles sintered due to the Ostwald ripening effect, which caused the pore blocking of the support and further led to the deactivation of the catalysts.

Highly Dispersed Nickel Particles Encapsulated in Multi‐hollow Silicalite‐1 Single Crystal Nanoboxes: Effects of Siliceous Deposits and Phosphorous Species on the Catalytic Performances

AbstractMulti‐hollow silicalite‐1 single crystals (MH) were prepared for the first time by an original synthesis pathway by using tetrabutylphosphonium hydroxide (TBPOH) as a mild desilicating agent. This new generation of hierarchical zeolite allowed the encapsulation of nanoparticles (NPs) featuring an enhanced confinement of the metallic guest and a thin wall thickness. The MH catalyst exhibited a better stability for methane steam reforming at 700 °C than a single‐hollow counterpart (SH). Ni average particle size could be kept lower than 4 nm after 20 h on stream for the MH sample. However, a detailed analysis of kinetic data of the structure‐insensitive CO methanation used as a model reaction revealed that the sample activity was adversely affected by two main factors deriving from the preparation steps. First, a siliceous over‐layer derived from the decomposition of intermediate Ni phyllosilicates, which partly covered the resulting Ni nanoparticles. Second, phosphorus from the templates remained in the samples, probably forming a Ni–P compound upon reduction. The overall catalytic activities observed here were therefore a complex interplay of improved dispersion and poisonous effects.

Morphology-controllable synthesis and thermal decomposition of Ag and Ni oxalate for Ag-Ni alloy electrical contact materials

Two silver and nickel oxalate precursors with different morphologies (plates and particulates) were synthesized via precipitation of Ag+ and Ni2+ ions by C2O42−. In the case of high oxalate concentration and low pH value, the precursor was composed of Ag2C2O4 hexagonal plates with NiC2O4·2H2O plates adhered onto the surfaces. Low oxalate concentration and neutral pH resulted in the formation of irregular silver and nickel oxalate particles. Metallic Ag-Ni powders can be directly obtained at 400°C in inert gas by thermal decomposition of the precursors. Finally, two Ag-matrix electrical contact materials reinforced by nickel with different morphologies (plates and particles) were prepared using the metallic Ag-Ni powders derived from the two typical precursors, respectively. Both samples show hardness and electrical conductivity that outperform the ASTM standard. The sample reinforced by Ni plates shows an even better performance of electrical conductivity. While the sample reinforced by dispersed nickel particles exhibits a better anti-arc and anti-erosion performance.

Highly active Ni2P/SiO2 catalysts phosphorized by triphenylphosphine in liquid phase for the hydrotreating reactions

A highly loaded and dispersed 60%Ni/SiO2 catalyst was phosphorized by triphenylphosphine (PPh3) in liquid phase for the preparation of highly loaded and dispersed Ni2P/SiO2 catalysts. It was found that without pre-reduction, the Ni/SiO2 was difficult to be phosphorized by PPh3, and large Ni2P particles were resulted at the high phosphidation temperatures (543–593K). When the Ni/SiO2 was pre-reduced, the highly dispersed nano nickel particles formed were easily phosphorized by PPh3 at the lower temperatures (443–543K). The resulted Ni2P/SiO2 catalyst phosphorized by PPh3 at 443K possessed small and homogeneous Ni2P particles (∼6nm) with the high Ni2P active site density (324μmol/g) as titrated by the adsorption of CO. It was significantly more active than the Ni2P/SiO2 catalyst phosphorized by PH3 in gas phase with the Ni2P active site density of 263μmol/g for the hydrodesulphurization of dibenzothiophene and hydrogenation of tetralin to decalin in a model diesel.

Synthesis Gas from Pyrolysis of Cedar Sawdust as Biomass Materials: Characterization and Catalytic Performance of Nickel-Based Monolithic Catalyst

A series of monolithic catalysts with different NiO loadings were prepared by supported on the acid treated cordierite. Their specific surface area, pore volume, pore distribution, and catalytic performance in the reforming reaction of biomass pyrolysis gas for synthesis gas were studied. The results show that the specific surface area and pore volume of the cordierite after acid treatment are up to 156 m(2)/g and 0.099 m(3)/g respectively. However, with increasing nickel oxide loading, the specific surface area and pore volume of the catalyst decrease greatly and then tend to steady. The effect of nickel oxide loading on gas composition is quite small, and the total content of H(2) and CO is maintained at 90%. The tar conversion is not affected by the specific surface area of the catalysts. After 6 h catalytic reaction, the structure of the catalysts with 28% NiO does not change, and the quantity of carbon deposition is about 1%. The tar conversion decreases from 87.4% to 81.3%. It is suggested that the nickel-based catalyst has relatively stable activity under high tar concentration conditions, which is attributed to the high dispersion of nickel particles on the support and high stability of the catalyst phase structure.

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.

Biogas reforming over bimetallic PdNi catalysts supported on phosphorus-modified alumina

A series of bimetallic PdNi catalysts supported on alumina modified with different amounts of phosphorus (0.5–5 wt%) were prepared. The effect of phosphorus content on the structure, surface properties and catalytic behavior of supported PdNi catalysts in biogas reforming was studied. The physicochemical properties of the samples were characterized by using different techniques: N 2 adsorption–desorption isotherms, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (TPD), thermogravimetric and differential thermal analysis (TG/DTA) and scanning transmission electron microscopy (STEM). The catalytic properties of the catalysts were evaluated in the reaction of reforming of methane with CO 2. It was shown that increasing the P content (≥1 wt%) leads to agglomeration of the metal Ni particles, as well as to increase of the total acidity of the catalysts. Within bimetallic system, the PdNi catalyst with 0.5 wt% phosphorus showed the best performance and stability caused by the presence of highly dispersed nickel particles on the catalyst surface due to the strong interaction between supported species and alumina.

Regenerable and durable catalyst for hydrogen production from ethanol steam reforming

In this work, perovskite-type oxides La 1− x Ca x Fe 0.7Ni 0.3O 3 were prepared by using a citrate complex method. The catalysts were employed in the reactions of steam reforming of ethanol (SRE) and oxidative steam reforming of ethanol (OSRE) to produce hydrogen. A reduction–oxidation cycle was proposed to overcome the problems of active component sintering and carbon deposition encountered in SRE reaction. In the ex-situ reactions, highly dispersed surface nickel particles formed during the reduction of La 1− x Ca x Fe 0.7Ni 0.3O 3, while during the introduction of an oxidative atmosphere these particles could be oxidized and restored back into the perovskite bulk. Owing to the existence of this segregation–incorporation cycle of nickel species in the perovskite oxides, the sintering of nickel particles under OSRE was found depressed effectively. Besides, this work proved that the oxygen in the feed is helpful to the elimination of deposited carbon. It seems promising for overcoming the problems of the active component sintering and carbon deposition in SRE reaction by regulating the redox ability of the perovskite-type oxides and the feed composition.

Temperature dependence of hydrogen adsorption properties of nickel-doped mesoporous silica

The temperature dependence of the hydrogen adsorption properties of nickel-doped mesoporous silica (MCM-41) synthesized by a direct hydrothermal method was investigated by measuring the amount of hydrogen adsorbed at pressures up to 100 kPa at 298, 373, and 473 K. Nickel-doped MCM-41 adsorbed more hydrogen than undoped MCM-41 and metallic nickel at ≈298/0, 373/0, and 473 K/0 kPa due to chemical adsorption enhanced by the highly dispersed nickel particles. Chemical adsorption increased with increasing nickel content and adsorption temperature, suggesting the presence of adsorption sites. The nickel doping also brought the spillover effect, which enhances the physical adsorption of hydrogen. The spillover effect was enhanced at high nickel contents and adsorption temperatures.

Influence of the chemical activation of carbon nanofibers on their use as catalyst support

Three nickel catalysts supported on carbon nanofibers (CNFs) have been prepared by deposition–precipitation (ca. 3%, w/w). The CNFs were prepared by catalytic chemical vapour decomposition of ethylene over a Ni/SiO 2 catalyst, and chemically activated with RbOH (CNF RbOH) and KOH (CNF KOH). The materials were characterized by transmission electron microscopy (TEM), N 2 adsorption–desorption, temperature-programmed oxidation, X-ray diffraction (XRD), acid–base titrations and temperature-programmed decomposition in helium. KOH was the most effective activating agent, developing carbon porosity, decreasing the crystalline character and increasing surface acidity to a higher extent. After nickel introduction, the catalysts were characterized by temperature-programmed reduction, XRD, TEM, N 2 adsorption–desorption and acid–base titrations. Surface-area weighted mean Ni particle diameters (post reduction at 400 °C) followed the sequence: Ni/CNF KOH (4.9 nm) < Ni/CNF RbOH (8.6 nm) < Ni/CNF (25.5 nm), where a further activation of the support led to smaller/better dispersed nickel particles. The surface acidity of the catalysts followed the sequence: Ni/CNF RbOH < Ni/CNF < Ni/CNF KOH. The gas phase hydrogenation of butyronitrile was used as a surface characterization test, where bigger nickel particles consistently developed higher catalytic activity. Selectivity, however, was not sensitive to metal particle size, but increased towards condensation products with increasing catalyst acidity.

Studies on nickel nanoparticle attachment on surface modified carbon nanotubes by wet chemical method

Wet chemical method is a relatively simple technique, which has been used for attaching nickel nanoparticles homogeneously on multi-walled carbon nanotubes (MWCNT). The MWCNT was synthesised by catalytic chemical vapour deposition (CCVD) method. The surface of MWCNT was modified by treating with boiling conc. nitric acid. Carbon nanotubes dispersed in nickel nitrate solution were heat treated with particular heating rate of 8°C/min from room temperature to 100°C under argon atmosphere and soaked at this temperature for 1 h before heating to 500°C at 4°C/min. The resultant product is found to be nanostructured nickel oxide attached to MWCNT. Subsequent reduction of the metal oxide in hydrogen atmosphere yielded nickel nanoparticles anchored to the surface of nanotubes. Chemical impregnation resulted in homogeneously dispersed nickel particles on the surface of oxidised MWCNT whereas in the case of unoxidised MWCNT uneven dispersion of nickel particle was observed. Results obtained on the characterisation of the products from XRD, SEM, TEM and EDX are presented. This simple method could allow large-scale production of functionalised MWCNT, which can be used as catalyst supports with high stability.