NiAl2O4 Spinel Research Articles

Physico-chemical properties and syngas production via dry reforming of methane over NiAl2O4 catalyst

Nano-particles of NiAl2O4 were prepared by co-precipitation and their bulk and surface were characterized by XRD, Raman spectroscopy, N2-adsorption-desorption analysis, SEM-EDS and XPS. The reducibility was studied by TPR and HTXRD techniques under H2 atmosphere. The synthetized catalyst was made of NiAl2O4 spinel oxide as main phase and of NiO (10%) free oxide. Interestingly, it was shown that the surface was richer in Al species. The catalytic performances in methane dry reforming were evaluated without H2-pretreatment of catalyst. A very high activity was observed with conversion of methane and CO2 at 750 °C of 84 and 90 mol%, respectively and high H2/CO ratio. The amount of coke deposited during the reaction on this spinel was ∼3.6%. The physico-chemical properties of the catalyst on their behavior in the dry reforming of methane are discussed.

A robust method to characterize rumpling in high-strength bond coats

A new method has been developed to nondestructively characterize bond coats that rumple during thermal cycling. This method employs Fourier transforms of 2D optical profilometer data and is applied to coatings that have differing tendencies to rumple such as (Pt,Ni)Al coatings and high-strength γ′ or γ+γ′ bond coats. The method isolates the 2D periodic undulations characteristic of rumpling from other inhomogeneous time-dependent phenomena that occur at the surface, including HfO2 and NiAl2O4 spinel oxide growth, bond coat swelling, and noisy data. The method is benchmarked against the traditional rumpling indicators seen in the literature, surface roughness and tortuosity, using synthetic datasets to explore the strengths and limitations of the algorithm. The versatility of this method to quantify rumpling is demonstrated on experimental datasets from a β-phase bond coat with high levels of noisy or missing data. Application of the method provides a quantification of the rumpling amplitude and wavelength that are confirmed with metallographic cross sections of the samples and predicted by the Balint and Hutchinson rumpling model. The algorithm correctly measures (in contrast to the RMS surface roughness) an increasing surface undulation amplitude during initial furnace cycling, followed by a decrease in undulation amplitude near the end of the coating life as TGO spallation becomes prevalent.

Design of NiAl2O4 cellular monoliths for catalytic applications

This work focuses on designing highly-porous cellular NiAl2O4-based spinel ceramics through combined suspension emulsification/reactive sintering and further decoration of the pore surfaces by Ni nanoparticles for potential applications in heterogeneous catalysis. Due to kinetic limitations and specific porous structure, the reduction occurs without affecting the integrity of the cellular monoliths. The reaction mechanism, assessed by XRD and TEM/EDS, includes both partial decomposition and reduction, resulting in the formation of metastable Al-enriched phases, mainly NiAl32O49, and metallic Ni phase, respectively. The results suggest that the cellular bulk framework can be decorated with Ni catalyst in a controlled way, by proper selection of the initial cation stoichiometry of the NiAl2O4 spinel and appropriate reduction conditions. In selected conditions the reduction results in Ni nanoparticles of various dimension scales, finely dispersed at the pore surfaces, with a significant fraction below 50nm, as confirmed by TEM/EDS. The results of thermodynamic analysis emphasize that the redox tolerance of the spinel phase is dependent on the Ni:Al activity ratio, suggesting the prospects for tuning the catalytic activity and stability by designing the initial composition and resulting content of metallic Ni and Ni- and Al-containing metastable phases.

Ceria promotion over Ni-containing hydrotalcite-derived catalysts for CO2methane reforming

The catalytic activity in dry methane reforming of hydrotalcite-derived catalysts with ceria and/or nickel species introduced into hydrotalcite interlayer spaces was examined. The prepared materials were characterized (XRF, XRD, FT-IR, H2-TPR and N2 sorption) and subsequently tested in CO2 methane reforming at 550 °C. The obtained results showed that the incorporation of nickel species between hydrotalcite layers resulted in active catalyst with no sign of carbon deposition. Additionally, a beneficial effect of ceria promotion was observed. Ceria-promoted sample exhibited higher activity, stability and selectivity towards DRM, which may be explained by the formation of small Ni crystallites and prevention of the formation of inactive NiAl2O4 spinel phase.

Fabrication and Characterization of High Performance Intermediate Temperature Alumina Substrate Supported Micro-Tubular SOFCs

The central challenge of solid oxide fuel cell (SOFC) technology lies in how to achieve sufficient robustness and reliability while significantly reducing system and operating cost. This paper studied a novel alumina substrate supported micro-tubular SOFC with high performance at intermediate temperatures. An in-house built extrusion system in combination with modified phase-inversion method was used to fabricate micro-tubular alumina substrate with radially well-aligned micro-channel array. The gas permeability of such an alumina substrate reached 69.2 × 105 Lm−2h−1, approximately ten times that of the substrate with conventional microstructures. The addition of NiO (10 wt%) sintering aid significantly improved the bending strength of α-Al2O3 substrate while forming NiAl2O4 spinel phase in the substrate. Built upon the fabrication of alumina substrate, anode electrode and electrolyte layers were fabricated through dip-coating and sintering process alternatively. A porous barrier layer strategy was employed to inhibit NiO in the anode layer from diffusing into the substrate during high temperature sintering process. The resulting dense electrolyte layer and anode functional layer with the thickness of ∼10 μm and ∼20 μm were obtained respectively. The alumina substrate supported micro-tubular SOFC with material system NiO-SDC/SDC/PrBaCo2O5+δ demonstrated the peak power density of ∼1420 mW cm−2 at 600°C, which is among the best performance of SOFCs with the same material system in open literature. The novel micro-tubular cell also demonstrated excellent thermal cycling stability. By replacing the high-cost rare-earth anode material with low-cost alumina, the novel design not only significantly reduced the cost but also improved the robustness and reliability of SOFCs.

Colored oxides with hibonite structure: A potential route to non-cobalt blue pigments

The crystal structure of hibonite with an ideal formula CaAl12O19 is hexagonal P63/mmc, isostructural with magnetoplumbite. Natural and synthetic hibonites have been widely studied for their formation, compositions, crystal structures, properties and applications. Recent increasing interest in its coloration has led to the search of inorganic pigments based on the hibonite structure. We present here the syntheses and characterization of hibonite compounds with a general formula of AAl12−xMxO19 (A = Ca, Sr, RE (rare earths) or any combination thereof; and M = Ni or Ni coupled with one of the following: Ti, Sn, Ge, Nb, Ta, Sb). Bright sky-blue to royal-blue colors are induced in these oxides prepared by conventional solid state reactions, as demonstrated in the solid solutions of CaAl12−2xNixTixO19 (x = 0–1) and Ca1−xLaxAl12−xNixO19 (x = 0–1). The values of color coordinates L*a*b* range from 64.5, −5.3, −18.5 to 57, −11.33, −30.38. Structure refinements of neutron powder diffraction data reveal that Ni preferably occupies the tetrahedral site in the hibonite structure, and magnetic susceptibility analysis confirms that this Ni is Ni2+. Optical measurements further verify that the observed blue color is due to d-d transitions of tetrahedral Ni2+. The preference of Ni2+ for the tetrahedral site is unusual because Ni2+ prefers the octahedral site in the spinel NiAl2O4. We attribute this unexpected behavior to the unusually large Al−O distances for the tetrahedral site in the hibonite structure. These blue hibonites exhibit excellent thermal stability, superior acid/base durability and better near-infrared reflectance than that of the commercial cobalt blue pigment. Our results suggest a potential route to the development of inexpensive, enduring and cobalt-free blue pigments. Synthesis and characterization methods are briefly reviewed for hibonite type of oxides, especially those with blue colors.

Synthesis of nickel aluminate nanoceramic compound from aluminum and nickel carbonate by mechanical alloying with subsequent annealing

The aim of present work was to produce pure nickel aluminate (NiAl2O4) nanoceramic compound by high energy milling of nickel carbonate (NiCO3) and aluminum (Al) powders followed by annealing. Phase composition, thermal behavior, morphology and microstructure of powder samples were characterized by means of X-ray diffraction, differential scanning calorimeter, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The results showed that formation of NiAl2O4 spinel compound from NiCO3 and Al powders took place in three steps: oxidation of Al to Al2O3, decomposition of NiCO3 to NiO and CO2, and finally the solid state reaction between Al2O3 and NiO. It was also demonstrated that single phase NiAl2O4 spinel compound can be produced by 5 h of mechanical milling with subsequent annealing of NiCO3/Al mixture at 900 °C for 2 h, which is ∼500 °C lower than the temperatures used in the traditional solid state methods. The particle diameter of the produced NiAl2O4 spinel compound was found to be less than 100 nm as measured by transmission electron microscopy.

Deactivation mechanism of Ni supported on Mg-Al spinel during autothermal reforming of model biogas

Nickel supported on Mg-Al oxides was studied in the autothermal reforming (ATR) of model biogas at 700°C. Ni/Mg0.4Al2O3.4 deactivated with time on stream and the cause of deactivation was investigated and identified. Ni was readily oxidized to NiO in the presence of O2. While NiO was essentially inactive for the reforming reaction, this oxide was yet active for methane combustion. Exhaustion of the O2 supply at front of the catalyst bed enabled the remaining CH4 to be steam and dry reformed on the metallic Ni left downstream. Gradual formation of NiAl2O4 spinel was also observed, likely caused by the higher temperature prevailing in the exothermic combustion zone that favors the diffusion of nickel cations into the alumina structure. In contrast to NiO, NiAl2O4 spinel was poorly active for CH4 oxidation. The frontline associated with the formation of the NiAl2O4 spinel phase eventually reached the end of the catalyst bed, resulting in a complete loss of activity. No significant coke deposition could be evidenced here. The Ni deactivation profile was adequately fitted using a methane ATR kinetic model that included a linear decrease in the number of Ni metallic sites. Addition of Rh/Mg1.1Al2O4.1 in front of a nickel-based catalyst led to a stable activity. Using this dual-bed system, no NiAl2O4 formation was identified after reaction.

Hydrogen production via methanol steam reforming over Ni-based catalysts: Influences of Lanthanum (La) addition and supports

The effect of the addition of Lanthanum (La), the different loading of nickel oxide and various supports on the catalytic performance of Ni-based catalysts was investigated for methanol steam reforming to produce hydrogen. TEM, N2 adsorption-desorption, XRD, and TPR were used to characterize the catalysts. Separated NiO particles, La–Ni or La–Ni–Al mixed oxides as well as NiAl2O4 spinel were detected. The results showed that the addition of lanthanum into Ni-based catalyst decreased the steamed temperature and the selectivity of CO. This change was closely associated with separated NiO particles with the smaller size and higher dispersion as well as the different interaction between NiO particles and support upon the modification of lanthanum. It was also found that the moderate loading of nickel facilitates the catalytic performance for methanol steam reforming due to the generation of separated NiO species with moderate particle size. Moreover, the different interaction strength between nickel species and support could give rise to the difference in the catalytic performance of active Ni species, depending on the support. The Al2O3 supported catalyst exhibits better conversion of CH3OH, higher hydrogen selectivity and lower CO selectivity than those of SiO2 and MgO supported catalysts.

Cation distribution in nanocrystalline (Co, Ni)Al2O4 Spinel

In the present study, the cations Co2+/Ni2+ and Al3+ distribution in nanocrystalline (Co, Ni)Al2O4 spinel have been investigated using X-ray and transmission electron microscopy. The nanocrystalline (Co, Ni)Al2O4 spinel has been synthesized using mechanically activated Al70Co15Ni15 quasicrystalline precursor through annealing at 600°C in controlled oxygen atmosphere. The mechanical activation of single phasic decagonal Al70Co15Ni15 quasicrystal was carried out in a high energy attritor ball mill for 40h with 40:1 ball to powder ratio using toluene as a process control agent. The high resolution x-ray diffraction data has been refined by the Rietveld method using JANA2006 and subsequently, the corresponding structure has been constructed using Diamond4.0. The structure was also confirmed by analysis of transmission electron microscopy linearized diffraction pattern profile of d-values and corresponding plane. These analyses indicate that the cations Co2+ and Ni2+ distributed in the tetrahedral coordinated sites are the dominant species in the normal spinel phase.

Highly active and stable alumina supported nickel nanoparticle catalysts for dry reforming of methane

A highly stable and extremely active nickel (Ni) nanoparticle catalyst, supported on porous γ-Al2O3 particles, was prepared by atomic layer deposition (ALD). The catalyst was employed to catalyze the reaction of dry reforming of methane (DRM). The catalyst initially gave a low conversion at 850°C, but the conversion increased with an increase in reaction time, and stabilized at 93% (1730Lh−1gNi−1 at 850°C). After regeneration, the catalyst showed a very high methane reforming rate (1840Lh−1gNi−1 at 850°C). The activated catalyst showed exceptionally high catalytic activity and excellent stability of DRM reaction in over 300h at temperatures that ranged from 700°C to 850°C. The excellent stability of the catalyst resulted from the formation of NiAl2O4 spinel. The high catalytic activity was due to the high dispersion of Ni nanoparticles deposited by ALD and the reduction of NiAl2O4 spinel to Ni during the DRM reaction at 850°C. It was verified that NiAl2O4 can be reduced to Ni in a reductive gas mixture (i.e., carbon monoxide and hydrogen) during the reaction at 850°C, but not by H2 alone.

Carbon dioxide reforming of methane over mesoporous nickel aluminate/γ-alumina composites

A series of xNiAl2O4/γ-Al2O3 composites with various Ni contents have been prepared via one-step partial hydrolysis of metal nitrate salts in the absence of surfactants and used for carbon dioxide reforming of methane. The characterization results demonstrated that the NiAl2O4/γ-Al2O3 materials possessed mesoporous structures of uniform pore sizes; and the Ni2+ ions were completely reacted with alumina to NiAl2O4 spinel in the matrices using N2 sorption, XRD, TEM, and XPS. The NiAl2O4/γ-Al2O3 materials exhibited excellent catalytic properties and superior long-term stability for carbon dioxide reforming of methane. The effects of Ni content on the intrinsic activities and the amounts of coke disposition of the xNiAl2O4/γ-Al2O3 catalysts were discussed in detail for the carbon dioxide reforming of methane. The results revealed that the Ni particle sizes did not affect the intrinsic activity of metallic Ni, but smaller Ni particles could reduce the rate of coke deposition.

Controllable synthesis of metallo-alkoxide precursor-derived nickel aluminate spinels using TEA-gel process and morphology-dependent reducibility

A study was made of the different preparation methods affecting the morphology and reducibility of the obtained NiAl2O4 spinels. The NiAl2O4 with various morphologies has been fabricated through the dependent control of TEA (triethanolamine) -gel parameters. Compared to the NiAl2O4 prepared from a direct calcination of spinel precursors, the superb structural characteristics of the NiAl2O4 including large surface area and well-defined interconnected nanoparticles were observed via the TEA-gel route. The NiAl2O4 prepared by TEA-gel method yields the highest degree of surface reduction with the largest amount of metallic nickel phase found in the spinels. This spinel also had the lowest initial temperature of reduction. The results indicate that the NiAl2O4 prepared by the TEA−gel technique using our new spinel alkoxide precursor has a promising prospect in the preparation of nickel catalyst supports where there is a need to avoid the traditional multiple procedures that are time-, solvent-as well as high energy-consuming.

Enhanced methane combustion performance over NiAl2O4-interface-promoted Pd/γ-Al2O3

Poor durability and low Pd utilization efficiency are the main drawbacks of supported Pd catalysts for low-temperature methane combustion. Here, we present a facile way to stabilize the performance of Pd/Al2O3 by introducing a spinel NiAl2O4 interface as a promoter at no cost to the activity. The NiAl2O4 interface is formed by impregnation of alumina supports in the nickel-containing solution, followed by high-temperature calcination. A series of 0.4wt.% Pd/xNiO/γ-Al2O3 with NiO loading varying among 0.0, 0.5, 1.0, and 9.0wt.% is investigated. The formation of a NiAl2O4 interface promotes the distribution and crystallization of PdO, suppresses PdO particles aggregation and surface OH− species accumulation during the reaction, and finally leads to the excellent performance of Pd/0.5NiO/γ-Al2O3. Pd/0.5NiO/γ-Al2O3 demonstrates higher Pd utilization efficiency than the state-of-the-art Pd-based catalysts and better stability than Pd/Al2O3. Such a spinel interface promotion strategy may bring new insight into the design of highly efficient Pd-based catalysts and their potential technological applications.

Characterization of composites containing NiAl2O4 spinel phase from Al2O3/NiO and Al2O3/Ni systems

This paper focused on the characterization of the composites containing nickel aluminate spinel from Al2O3/NiO and Al2O3/Ni systems. The composites were prepared by die pressing of powders and subsequent sintering of green bodies in air atmosphere. Composites were characterized by XRD, SEM, EDS and DTA/TG/MS analyses. The physical properties of the composites were measured by Archimedes method. Quantitative description of the composites microstructure was made on the basis of SEM images using computer image analysis. The XRD studies and SEM observations of composites confirmed the presence of two phases Al2O3 and NiAl2O4 in the whole volume of samples from both systems. Spinel phase was evenly distributed throughout the volume of the material. Morphology of NiAl2O4 obtained from both systems was characterized by the presence of voids. The DTA/TG/MS measurements showed the characteristics of organic binder decomposition and type of gases released to the atmosphere during thermal treatment. Moreover, the DTA/TG analysis showed the temperature of spinel-phase formation for both systems. It was found that the spinel-phase NiAl2O4 formation retards the process of densification. Therefore, it can be concluded that densification of samples with spinel phase depends mainly on the volume of spinel phase in composite material and does not depend on the substrates used to prepare spinel phase. The values of the selected properties of Al2O3–Ni- and Al2O3–NiO-based materials confirmed that the physical properties depend on the type of substrates used in the fabrication of composites. The type of powder influences the open porosity of samples. For composites produced using NiO powder, open porosity is lower than for samples formed with nickel powder.

Sol–gel vs. impregnation preparation of MgO and CeO2 doped Ni/Al2O3 nanocatalysts used in dry reforming of methane: Effect of process conditions, synthesis method and support composition

Ni/Al2O3–CeO2 and Ni/Al2O3–MgO nanocatalysts were prepared by impregnation and sol–gel methods and used in CO2 reforming of methane. The research aimed at the effects of cerium and magnesium addition in sol–gel method on the catalytic properties and performance of Ni/Al2O3 catalyst. All the samples were characterized by XRD, FESEM, PSD, EDX, BET, FTIR and TG-DTG techniques. XRD results confirm reinforced impact of sol–gel method on NiO dispersion in the presence of support promoters. Besides, it proves the potential of the sol–gel method in enhancement of metal-support interaction via NiAl2O4 spinel formation. FESEM images demonstrate smaller and more uniform nanoparticles as a result of utilizing the sol–gel method, especially when CeO2 is used. More than 94% of surface nanoparticles lie between 10 and 40 nm with surface average particle size of 23.3 nm. Apart from revealing the suitability of adopted calcination temperatures, TG-DTG analysis supports the higher surface area for sol–gel made samples which was evidenced by BET analysis. Catalytic evaluation revealed that better performance is obtained by employment of sol–gel method and support promotion. Both of the sol–gel synthesized Ni/Al2O3–CeO2 and Ni/Al2O3–MgO nanocatalysts exhibited the superior and stable catalytic activity during 1440 min at 850 °C, indicating the synergistic effect of sol–gel method and promoter addition. However, sol–gel synthesized Ni/Al2O3–CeO2 nanocatalyst was found to be the most proper choice for CO2 reforming of methane, exhibiting the H2/CO ratio of 1 and H2 yield of 94% at 850 °C.

Effects of adding alumina to the nickel-zirconia anode materials for solid oxide fuel cells and a two-step sintering method for half-cells

The co-sintering process of half-cells has an important effect on the flatness and performance of solid oxide fuel cells. In this study, we report a two-step sintering method to fabricate flat three-layer half-cells. The first sintering step is a freestanding sintering process at a low temperature (1280 °C). The second sintering step is a constrained sintering process at 1400 °C. The shrinkage of the anode support layer (ASL) and the curvature of the half-cell can be adjusted by adding Al2O3 into the ASL in the first sintering step. Effects of Al2O3 addition on the NiO-YSZ anode material are also studied. We find that NiO reacts with Al2O3 to form NiAl2O4 spinel at the early sintering stage. This reaction transiently promotes the grain growth of NiO. Once the reaction terminates and the NiAl2O4 spinel is formed, the grain growth of NiO will be suppressed, even at higher sintering temperatures. Our results indicate that by a proper amount (approximately 0.2 wt%) of Al2O3 addition, smaller NiO grains can be obtained while the side effects of NiAl2O4 are negligible, which is favorable to increase the conductivity and stability of the ASL, and can enhance the performance of SOFC.

Effect of Calcination Temperature on the Structure and Catalytic Performance of the Ni/Al2O3 and Ni–Ce/Al2O3 Catalysts in Oxidative Dehydrogenation of Ethane

We studied the effect of calcination temperature of Ni/Al2O3 and Ni–Ce/Al2O3 catalysts on the specific surface area, acidity, ratio of pore volume and specific surface area, reducibility reflecting the changing population of Ni(Td) and Ni(Oh) species, and activity/selectivity in oxidative dehydrogenation of ethane. It should be stressed that the role of Ce as a promoter on the catalytic activity of Ni–Ce/Al2O3 catalysts decreased with an increasing value of the calcination temperature. At a reaction temperature of 500 °C, the highest productivity to ethene was observed for the Ni–Ce/Al2O3 catalyst calcined at 500 °C. Ni–Ce/Al2O3 catalysts calcined at 500–750 °C showed the same selectivity to ethene. The Ni–Ce/Al2O3 catalysts calcined at 900 and 1000 °C showed a sharp decrease in the selectivity and the activity, which was probably associated with the formation of NiAl2O4 spinel.

Effect of thermal treatment on the synthesis of NiAl 2 O 4 spinel oxide using chitosan as precursor

Abstract Nickel aluminate oxide (NiAl2O4) was prepared using chitosan as polymeric precursor and ammonia solution as a precipitating agent. In addition, nickel nitrate and aluminum nitrate salts were used as sources of Ni and Al, under stoichiometric amounts (molar ratio Ni:Al = 1:2). NiAl2O4 particles were prepared at different calcination temperatures and their properties were investigated. The synthesized materials were characterized by X-ray diffraction, infrared spectroscopy, atomic force microscopy, thermogravimetric analysis and nitrogen adsorption-desorption isotherms. The results showed that the thermal treatment process strongly influence on the formation of a single-phase structure of NiAl2O4 spinel. Nickel aluminate spinel with a porous structure and high surface area was obtained at temperatures above 700 ºC.

Effect of support on the performance of Ni-based catalyst in methane dry reforming

Ni-based catalysts with different supports were prepared and characterized by N2 physisorption, XRD, H2-TPR, H2 chemisorption, and so on; the effect of support on the performance of Ni-based catalyst in methane dry reforming was then investigated. The results indicated that the support has a significant influence on the state of NiO species. SiO2, TiO2 and ZrO2 as a support have a weak interaction with NiO, which facilitates the reduction of the corresponding catalysts; however, the weak interaction may also lead to quick deactivation due to the agglomeration of active metal species. Al2O3 and MgO have a strong interaction with NiO, which may promote the formation of NiAl2O4 spinel and NiO-MgO solid solution, respectively, and make the reduction of corresponding catalysts very difficult. Al2O3 modified by MgO is provided with both proper textural properties and interaction strength between metal and support, which are in favor of the dispersion and stabilization of NiO species. As a result, NiO supported on MgO-modified Al2O3 exhibits superior catalytic performance in methane dry reforming even under very high gas hourly space velocity; it is quite stable during a long term test of more than 100 h.