NiAl2O4 Phase Research Articles

Favorable formation of needle-shaped NiAl2O4 phase over macroporous Ni/CexZr1-xO2–Al2O3 catalysts in one-pot preparation and coke-resistant catalytic performance in dry reforming of methane

In this study, we report the formation of needle-shaped NiAl2O4 via favorable interactions between Ni and Al species over macroporous Ni/CexZr1-xO2–Al2O3 catalysts for dry reforming of methane (DRM) and its remarkable improvement in the catalytic performance. The macroporous catalysts prepared by a one-pot (OP) method promote a favorable interaction between Ni and Al species that results in the formation of unique needle-shaped NiAl2O4 due to easy access to each other compared with that by incipient wetness impregnation. The NiAl2O4 phase in the calcined catalysts transforms into highly dispersed Ni and defective Al2O3 via the Ni exsolution in the reduction step. The presence of oxygen vacancies near Ni0 species facilitates the CO2 activation and enhances the catalyst stability over DRM. The optimized distribution of active sites with abundant defects over macroporous Ni/CexZr1-xO2-Al2O3 catalysts (OP) result in high conversions of CH4 and CO2 and a low coking rate in DRM.

Ceramic-metal pipes with NiAl2O4 and TiAl2O5 spinel phases with different metallic phase content - Analysis of properties, and microstructure, taking into account LCA

The article describes the formation of samples into pipes with NiAl2O4 and TiAl2O5 spinel phases with different metallic phase content. The centrifugal slip casting method was used to form the composites. All suspensions used were shear thinning and were characterized by slight thixotropy. The analysis of the phase composition and chemical composition showed the presence of Al2O3, TiAl2O5 and NiAl2O4 in the produced samples. The produced materials were characterized by brittle fracture behaviour. The obtained life cycle assessment results clearly showed that as the content of the metallic phase increases, the environmental footprint of sinters in the A1 phase increases, which is a direct consequence of the increased use of raw materials.

The influence of Ti/Ni metallic phase content on the microstructure and environmental interactions of gradient Al2O3-based composites

Al2O3/Ti/Ni composites, enhanced with the inclusion of NiAl2O4 and TiAl2O5 phases, represent a novel class of advanced materials with multifaceted properties suitable for diverse engineering applications. Centrifugal slip casting method was used for preparation of two series of gradient Al2O3/Ti/Ni composite samples with different content of the metallic Ti and Ni phases. Series I containing 0.5 vol.% of Ni and 0.5 vol.% of Ti and Series II containing 2.5 vol.% of Ni and 2.5 vol.% of Ti. Each series contained 55 vol.% of a solid phase. Rheological properties of the suspensions as well as microstructure of the obtained composites were studied, with special attention paid to the analysis of the formed spinel phases. Both series in the green form were characterized by 3-zone structure with different metallic phase content. The widths of individual zones for the Series I and Series II, after sintering at 1450?C, were 0.53mm (zone I), 3.26mm (zone II), 0.8mm (zone III) and 1.27mm (zone I), 1.47mm (zone II), 1.87mm (zone III), respectively. The results showed that after sintering two spinel phases were formed. The NiAl2O4 spinel phase consists only of small grains with a size of approximately 1.3- 1.8 ?m, which form larger clusters with or without a void inside. The TiAl2O5 phase consists of grains with an average size of 4.3 to 4.5 ?m. The Life Cycle Assessment analysis revealed that the values of the global warming potential indicator in phase A1 are 0.16 kg and 0.20 kg equivalent of CO2 per sintered sample for the Series I and Series II, respectively.

The complementary relationship between Ru/Al2O3 and Ni/Al2O3 catalyst for dry reforming of methane

We report a physical mixture of 1 wt% Ru/Al2O3 with 10 wt% Ni/Al2O3 obtained from the NiAl2O4 phase as a highly active, durable, and cost-effective catalyst for the dry reforming of methane (DRM). Since the presence of Ru facilitates the reduction of Ni oxides, resulting in not only enhanced CH4 conversion but also increased carbon deposits, the optimal formation of metallic Ni sites is a key factor for the mixed Ru-Ni catalyst. Here, we used a NiAl2O4/Al2O3 catalyst and reduced it with CH4 under reaction conditions for the limited formation of metallic Ni sites, depending on the reaction temperatures. As a result, this mixed catalyst showed higher performance for DRM than a Ru single catalyst with mild carbon deposits at both low (650 ℃) and high (800 ℃) temperatures taking advantage of improved cost-effectiveness, on top of that, the existence of a Ni catalyst compensated for the loss of activity of a Ru catalyst due to sintering. We also suggest different mechanisms for DRM over the Ru catalyst and Ni catalyst respectively from the results of temperature-programmed surface reaction and CH4/CO2 cycling experiments.

The effect of amorphous coating on high temperature oxidation resistance of Ni-based single crystal superalloy

Amorphous Al2O3 coating was prepared on Ni-based single crystal superalloy via atomic layer deposition (ALD) for high temperature oxidation protection. The oxygen inward transport and outward-cation diffusion were hindered by amorphous Al2O3 coating, and the coated alloy showed high oxidation resistance. The low oxygen partial pressure at the alloy/coating interface altered the alloy oxidation behavior, allowing the priority oxidation of protective Al and Cr elements. The oxidation process was controlled by the growth of Cr2O3 and Al2O3. The coating exhibited high spallation resistance. Degradation of the coating, the formation of NiAl2O4 phase in amorphous Al2O3 layer, was observed.

A Highly Active NiMoAl Catalyst Prepared by a Solvothermal Method for the Hydrogenation of Methyl Acrylate

In this study, a series of Ni10MoxAl composite metal oxide (Ni10MoxAl, NiO = 10 wt.%, x = 2.5, 5, 10, 15, 20 wt.%) catalysts with different Mo content were prepared by a solvothermal method using a water—ethanol system. By employing various characterization technologies, it was confirmed that the suitable amount of the Mo element can not only promote the dispersion of the Ni species but also inhibit the formation of the inactive NiAl2O4 phase. Consequently, the hydrogenation activity of the Ni10MoxAl catalysts was affected by the particle size of the active components and the amount of the NiAl2O4 phase. As a result, the Ni10Mo10Al catalyst showed the best catalytic performance on methyl acrylate hydrogenation, and the yield of methyl propionate can be increased from 53.7% to 89.5% at 100 °C and 1 MP H2, compared with the Ni10Mo10/γ–Al2O3 catalyst prepared by a traditional impregnation method. The stability of the Ni10Mo10Al catalyst was also investigated, and the catalyst can run stably for 23 h. The novel strategy adopted in this article provides a new direction for the preparation of high activity Ni–Mo catalysts.

Preparation of a Novel NiAlO Composite Oxide Catalyst for the Dehydrogenation of Methylcyclohexane

A series of NiAlO composite oxide catalysts with high surface areas and high Ni dispersion were prepared through an improved co-precipitation method. The new preparation method effectively improved the specific surface area and pore volume of the catalyst, promoted the dispersion of nickel species, alleviated the agglomeration of the catalyst, and improved the stability of the catalyst by strengthening the interaction between Ni and Al. The typical catalyst Ni20Al had a specific surface area of 359 m2/g and a NiAl2O4 phase. In the dehydrogenation of methylcyclohexane over the Ni20Al catalyst, the conversion of methylcyclohexane could reach 77.4%, with toluene selectivity of 85.6%, and a hydrogen release rate of 63.94 mmol g−1 h−1, and did not show any significant inactivation during the stability test over 29 h under the reaction conditions of reaction temperature 450 °C and LHSV = 4 mL g−1 h−1. However, the conversion of methylcyclohexane with the IM-NiAl catalyst prepared through the traditional impregnation method was only 50.75%, with toluene selectivity of 70.5%, and with a hydrogen release rate of 35.84 mmol g−1 h−1, and the lifetime of the catalyst was only 15 h.

Crystallization and pyrolysis of nitric acid pressure leach liquor of limonitic laterite and separation of valuable metals

Based on the advantages of nitric acid pressure process (NAPL) for laterite nickel ores, this study innovatively proposes nitric acid pressure leach liquor crystallization pyrolysis-mixed metal oxides separation process. Firstly, the feasibility and the possible reactions of mixed nitrate pyrolysis were confirmed by thermodynamic analysis. Subsequently, the optimal pyrolysis temperature was experimentally investigated. Then, the pyrolysis process of combined nitrate was thermodynamically analyzed, and the phase composition of mixed metal oxides was determined by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS). The Pourbaix diagram shows that using NaOH as leaching agent can selectively separate aluminum from mixed metal oxides, and the variables influencing aluminum's leaching rate are investigated. The experimental results are as follows: the optimal pyrolysis temperature of mixed nitrate crystals is 600 °C; the pyrolysis products are mainly oxides with the formation of NiAl2O4 and MgAl2O4 spinel phases; the aluminum leaching rate is 81.9% under the optimal alkali leaching conditions. The presence of spinel phase is not favorable for aluminum leaching. After leaching, an enriched residue of 15.8% Ni, 1.9% Co and 0.19% Sc was obtained.

Interactions of Ni/ZnO with alumina support and their influence on deep reactive adsorption desulfurization

Double hydrolysis mesoporous alumina (DHA) synthesized via hydrothermal technique and used as support for the loading of ZnO and Ni. The desulfurization activities and their interactions of Ni/ZnO/DHA adsorbents were compared with Ni/ZnO supported on commercially prepared alumina (Com). The higher breakthrough desulfurization activity and sulfur adsorption capability of these catalysts are influenced by the binding extant of Zn/Ni atoms with Al2O3 support, more free ZnO/Ni species and the formation of inactive ZnAl2O4 phases. The catalysts were characterized using nuclear magnetic resonance (NMR) spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, H2-temperature programmed reduction (H2-TPR) and N2 adsorption-desorption. Desulfurization activity shows that Ni/ZnO/DHA-80 °C catalyst achieved an excellent breakthrough sulfur removal (10 mg/L) up to 30.26 mL responsible for 110.4 mg S/g sulphur adsorption capability. This desulfurization performance is one fourth fold higher as compared to commercial Ni/ZnO/Com catalyst, achieving a compromised desulfurization activity of 1300 mg/L at set 30.26 mL model fuel flow with 38 mg S/g accumulative sulfur capacity. Detailed characterization results show that, the superior desulfurization activity shown by Ni/ZnO/DHA catalyst is due to the presence of meagre amount of unsaturated pentacoordinate Al3+ centers on Ni/ZnO/DHA surface which are responsible for lesser interaction of Ni/ZnO with Al2O4 and reduce the formation of inactive spinal ZnAl2O4 and NiAl2O4 phase even after many regeneration cycles which increases the active ZnO molar concentration as compared to Ni/ZnO/Com catalyst.

Characterization of Al2O3 Matrix Composites Fabricated via the Slip Casting Method Using NiAl-Al2O3 Composite Powder.

This work aimed to characterize Al2O3 matrix composites fabricated by the slip casting method using NiAl-Al2O3 composite powder as the initial powder. The composite powder, consisting of NiAl + 30 wt.% Al2O3, was obtained by mechanical alloying of Al2O3, Al, and Ni powders. The composite powder was added to the Al2O3 powder to prepare the final powder for the slip casting method. The stained composite samples presented high density. EDX and XRD analyses showed that the sintering process of the samples in an air atmosphere caused the formation of the NiAl2O4 spinel phase. Finally, the phase composition of the composites changed from the initial phases of Al2O3 and NiAl to Al2O3, Ni, and NiAl2O4. However, in the area of Ni, fine Al2O3 particles remaining from the initial composite powder were visible. It can be concluded that after slip casting, after starting with Al2O3 and the composite powder (NiAl-Al2O3) and upon sintering in air, ceramic matrix composites with Ni and NiAl2O4 phases, complex structures, high-quality sintered samples, and favorable mechanical properties were obtained.

Characterization, kinetics and stability studies of NiO and CuO supported by Al2O3, ZrO2, CeO2 and their combinations in chemical looping combustion

This study investigates the synthesized NiO- and CuO-based carriers supported by Al2O3, CeO2, ZrO2 and their combinations in chemical looping combustion (CLC). The oxygen carriers were tested in a thermogravimetric analyzer (TGA), where the results showed that the oxygen capacity increased using mixed support oxides in both NiO-based and CuO-based samples. The reducibility of CeO2 played a role in the increase of oxygen capacity and in the case of NiO-based samples, the reduction of NiAl2O4 phase as promoted by the formation of CeAlO3 played a role, as well. For NiO-based samples, a significant increase of carbon deposition occurred for mixed support oxides (Al2O3-ZrO2, Al2O3-CeO2 and Al2O3-ZrO2-CeO2) at 750 °C in comparison with the use of one support while the differences were negligible at 950 °C. To examine the structure and properties of the oxygen carriers, they were characterized by XRD, SEM/EDX and XPS. Comparison of fresh and used samples revealed sintering of active-sites particles on the surface of supports as evident of EDX mapping images and the decrease in active-site to support ratio in the XPS analysis. NiO/Al2O3-ZrO2-CeO2 was found to be a potential oxygen carrier for further CLC studies and scaleup.

CO2 Hydrogenation on NixMg1−xAl2O4: A Comparative Study of MgAl2O4 and NiAl2O4

Due to the increasing attention focused on global warming, many studies on reducing CO2 emissions and developing sustainable energy strategies have recently been performed. One of the approaches is CO2 methanation, transforming CO2 into methane. Such transformation (CO2 + 4H2 → CH4 + 2H2O) provides advantages of carbon liquification, storage, etc. In this study, we investigated CO2 methanation on nickel–magnesium–alumina catalysts both experimentally and computationally. We synthesized the catalysts using a precipitation method, and performed X-ray diffraction, temperature-programmed reduction, and N2 adsorption–desorption tests to characterize their physical and chemical properties. NiAl2O4 and MgAl2O4 phases were clearly observed in the catalysts. In addition, we conducted CO2 hydrogenation experiments by varying with temperatures to understand the reaction. Our results showed that CO2 conversion increases with Ni concentration and that MgAl2O4 exhibits high selectivity for CO. Density functional theory calculations explained the origin of this selectivity. Simulations predicted that adsorbed CO on MgAl2O4(100) weakly binds to the surface and prefers to desorb from the surface than undergoing further hydrogenation. Electronic structure analysis showed that the absence of a d orbital in MgAl2O4(100) is responsible for the weak binding of CO to MgAl2O4. We believe that this finding regarding the origin of the CO selectivity of MgAl2O4 provides fundamental insight for the design methanation catalysts.

Synergy Effects of Cobalt Oxides on Ni/Co-Embedded Al2O3 for Hydrogen-Rich Syngas Production by Steam Reforming of Propane

The synergetic effects of Co oxides on the Ni/CoAl (NCA) catalysts were observed at an optimal molar ratio of Al/Co = 2 (NCA(2)) due to the partial formations of thermally stable spinel CoAl2O4 phases for the steam reforming of propane (SRP). The optimal content of the spinel CoAl2O4 phases on the NCA(2) was responsible for the formation of the relatively active oxophilic metallic Co nanoparticles with a smaller amount of less active NiAl2O4 on the surfaces by preserving the relative amount of metallic Co of 68% and 52% in the reduced and used catalysts, which enhanced the catalytic activity and stability with the largest specific rate of 1.37 C3H8/(Ni + Co)h−1 among the tested NCA catalysts. The larger or smaller amounts of Co metal on the less active NCA mainly caused the preferential formation of larger aggregated Ni nanoparticles ~16 nm in size due to their weaker interactions, or induced the smaller formations of active metal phases by selectively forming the spinel NiAl2O4 phases with ~60% in the NCA(4), resulting in a fast deactivation.

Enhancement of heavy vacuum gas oil desulfurization via using developed catalyst based on Al2O3

In past few decades, a strong attention is paid to develop high-active catalysts for hydrotreating of the heavy vacuum gas oil (HVGO). In an agreement with that claim, this research work reports the synthesis of a developed catalyst for desulfurization of a petroleum HVGO fraction. Particularly, the catalytic performance of the catalyst, which was made via addition of CeO2 to ɣ alumina as supports for a trimetallic composite (CoNiMo-Al2O3), toward sulfur removal was investigated. For proper comparison, the activity of alumina individually-supported trimetallic catalyst CoNiMo-ɣAl2O3 at such application was also studied. The as-prepared catalysts were characterized by N2 physical adsorption/desorption (BET), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Catalytic activity was conducted in continuous flow trickle-bed reactor at various operating condition of temperature (320-380 °C), pressure (20-60 bar) and liquid hour space velocity (1-2.5 h-1). It was found that CoNiMo/CeO2-ɣAl2O3 was of a higher catalytic efficiency to hydrotreating of HVGO than that of CoNiMo-Al2O3. Numerically, CoNiMo/CeO2-ɣAl2O3 could successfully remove 83.5 % of sulfur compounds while it was only 66.2% in case of CoNiMo-Al2O3. The increased catalytic performance of ceria containing composite may be due to its high specific surface area (∼198.4 m2·g−1) and small crystallite size (24.24 nm). Moreover, the incorporation of CeO2 to alumina could subsequently inhibit the interaction between Ni and alumina; hence the inactive NiAl2O4 phase had not been formed. Thus, an enhanced catalytic desulfurization process could be attained.

Analysis of structure and microhardness of Al2O3-40 wt.% TiO2/NiCoCrAl gradient coating with in-situ needle-like phase reinforcement after high-temperature treatment

Abstract This study investigated the structural evolution and microhardness of Al2O3–40 wt.% TiO2/NiCoCrAl gradient coatings deposited by atmospheric plasma spraying (APS) after high-temperature treatment carried out at 800 °C in air for 600 h. The gradient region exhibited a different ceramic growth and oxidation behaviour at different zones. The nonhomogeneous needle-like γ-Al2O3 phase was formed at the ceramic region, whereas the homogeneous needle-like NiAl2O4 phase was formed at the NiCoCrAl oxidation region close to the ceramic coating. And the ingrowth Cr-rich phase existed inside the NiCoCrAl splats at the gradient region close to the bond coating. An obviously microhardness improvement of the coating can be measured by a Vickers microhardness tester. The formation of the needle-like phase has an effect on the reinforcement of coating.

Ethylene glycol dry reforming on Ni/Al2O3 catalyst for syngas generation

It is the first time ethylene glycol dry reforming (EGDR) reaction was carried out for syngas production on 10%Ni/Al2O3 catalyst in a tubular fixed-bed reactor at atmospheric condition. Wet-impregnation method was employed for the synthesis of 10%Ni/Al2O3 catalyst. The results of X-ray diffraction measurement revealed the presence of γ-Al2O3, NiO, NiAl2O4, Ni0 and graphitic carbon phases on the surface of spent 10%Ni/Al2O3 catalyst. H2 temperature-programmed reduction indicates that NiO and NiAl2O4 phases were totally reduced to metallic nickel phase at reduction temperature above 970 K. EGDR activity appeared to be steady with time-on-stream beyond 5-7 h. Catalytic activity was considerably improved with increasing feed ratio of CO2:C2H6O2 from 1:1 to 2.5:1.

The usage of carbon dioxide gas on pyrolysis process and its effect on biomass catalytic conversion

Several advantages of the usage of CO2 gas in pyrolysis theoretically could be the role for thermal efficiency, elimination oxygenated group, deep decomposition of biomass. The aim of this study was the use carbon dioxide as carrier gas and its effect on the catalytic product distribution from the rice husk type biomass. The Nickel/Alumina catalyst was prepared by impregnation method and calcination process of the Ni(NO3)2. 6H2O and Al2O3 mixture. The characterization was also performed by XRD analysis and BET adsorption method. The XRD analysis confirm the high crystallinity of NiO and NiAl2O4 phase which is considered as the interaction result between the NiO particle and the surface of γ-Al2O3. But the result of BET method suggested that the blockage the pore mouth of catalyst support γ-Al2O3 which is more likely due to the excessive amount of NiO particles. The comparison of pyrolysis carrier gas between CO2 and N2 and the variation of the operating temperature were performed to determine the product distribution distinctions. The catalytic conversion was done under the temperature 450, 475, 500, and 525°C. Experimental results show that the variation of carrier gas of the pyrolysis process and the variation of operating temperatures resulted in a difference product distribution. The dominant compounds formed as the temperature increases were ketone and benzene compounds.

Oxidation Behavior of Non-Modified and Rhodium- or Palladium-Modified Aluminide Coatings Deposited on CMSX-4 Superalloy

Rhodium-modified as well as palladium-modified and non-modified aluminide coatings on CMSX-4 Ni-based superalloy were oxidized in air atmosphere at 1100 °C. Uncoated substrate of CMSX-4 superalloy was also oxidized. The microstructure of coatings before oxidation consists of two layers: an additive and an interdiffusion one. The NiAl intermetallic phase was found in the microstructure of non-modified coatings, while the (Ni,Rh)Al intermetallic phase was observed in the microstructure of rhodium-modified aluminide coatings before oxidation. The (Ni,Pd)Al phase of palladium-modified aluminide coatings in the additive layer was observed before oxidation. The microstructure of the oxidized non-modified coatings consists of the γ’-Ni3Al phase. The oxide layer (10 µm thick) consists of the NiAl2O4 phase and porous Ni-rich oxide. The oxide layers (5 µm thick) formed on the surface of rhodium or palladium-modified coatings consist of the α-Al2O3 phase and the top layer of the NiAl2O4 phase. Al-depleted (30 at. %) β-NiAl grains besides the γ’-Ni3Al phase were found in the rhodium-modified coating, while only the γ’-Ni3Al phase region was revealed in the palladium-modified coating, Rhodium-modified coatings with small rhodium content (0.5 µm rhodium layer thick) can be an alternative for palladium-modified ones with bigger palladium content (3 µm thick palladium layer).

Microstructure Characterization of Metal Mixed Oxides

ABSTRACTThe microstructure of Ni-Mg-Al mixed oxides obtained by thermal decomposition of hydrotalcite-like compounds synthesized by a co-precipitation method has been studied by using X-ray diffraction (XRD) and atomic resolution transmission electron microscopy (TEM). XRD patterns revealed the formation of NixMg1-xO (x=0÷1), α-Al2O3 and traces of MgAl2O4 and NiAl2O4 phases. The peaks profile analysis indicated a small grain size, microdeformations and partial overlapping of peaks due to phases with different, but similar interplanar spacings. The microdeformations point out the presence of dislocations and the peaks shift associated with the presence of excess vacancies. The use of atomic resolution TEM made it possible to identify the phases, directly observe dislocations and demonstrate the vacancies excess. Atomic resolution TEM is achieved by applying an Exit Wave Reconstruction procedure with 40 low dose images taken at different defocus. The current results suggest that vacancies of metals are predominant in MgO (NiO) crystals and that vacancies of Oxygen are predominant in Al2O3 crystals.

Facile one-step synthesis of mesoporous Ni-Mg-Al catalyst for syngas production using coupled methane reforming process

Mesoporous Ni-Mg-Al and Ni-Al catalysts were facilely synthesized via evaporation-induced self-assembly (EISA) method and employed for coupled reforming reaction consisting of dry reforming of methane (DRM) and partial oxidation of methane (POM) to produce syngas (H2+CO). The Ni-Mg-Al and Ni-Al catalysts with encapsulated nickel nanoparticles were directly synthesized in one-pot way. For comparison, Ni/Al2O3 as reference catalyst was also prepared by general impregnation method. Characterization by BET, XRD and H2-chemisorption revealed that the Ni-Mg-Al catalyst owned larger surface area and higher Ni dispersion as well as smaller metallic Ni particles size compared to Ni-Al and Ni/Al2O3 catalysts. CO2-TPD demonstrated that the Ni-Mg-Al catalyst presented stronger basicity due to Mg incorporation. H2-TPR confirmed that the reduction of Ni-based species to Ni0 was performed in high temperature due to the formed NiAl2O4 phase. Activity tests indicated that this Ni-Mg-Al catalyst, due to its excellent physicochemical property, exhibited higher CH4 conversion, H2 selectivity, and H2/CO ratio in the coupled DRM-POM reaction. XRD, SEM and TG-DTA analyses of the used catalysts disclosed that the Mg-modified Ni-Mg-Al catalyst for syngas production using coupled DRM-POM reaction exhibited robust resistance to coke deposition. Consequently, by the synergistic cooperation between the coupled DRM-POM reaction and Mg-modified Ni-Mg-Al catalyst, high catalytic activity and stability could be accomplished to produce syngas.