Dry Reforming Of CH4 Research Articles

Evidence of undissociated CO2 involved in the process of C-H bond activation in dry reforming of CH4

We investigate here systematically C-H bond activation mechanism on Pt/MgO with O2, H2O and CO2, and find that dry reforming of CH4 (DRM) experiences a weak activity compared with reforming or partial oxidation of CH4. Pressure dependence shows negligible effect of CO determined within a broad CO pressure regime (<10 kPa at high-pressure CH4/CO2 (20.3 kPa) and <0.3 kPa at low-pressure CH4/CO2 (0.8 kPa)) and competitive adsorption between CH4 and CO2 (0.8 kPa), suggesting that CO2 is involved in CH4 activation as an entire molecule. Based on established Langmuir-Hinshelwood model, reaction between adsorbed CH4 and CO2 to yield formate and methyl species was kinetically relevant. Both CO2 and CH4 derivatives are the most abundant surface intermediates, being confirmed by in situ FTIR and quasi-in-situ XPS. The oxidizability of oxidant was quantitatively evaluated; CO2 has the weakest oxidizability, probably making DRM less active. DRM is structure-sensitive with terrace site of Pt as active component. The influence of reverse water–gas shift was dominant in modifying selectivity. This work will certainly reconcile contradictories on CH4 activation mechanism and push the industrial application of CH4 forward.

Plasma-assisted CO2 reforming of methane over Ni-based catalysts: Promoting role of Ag and Sn secondary metals

Carbon dioxide (CO2) and methane (CH4) are the primary greenhouse gases (GHGs) that drive global climate change. CO2 reforming of CH4 or dry reforming of CH4 (DRM) is used for the simultaneous conversion of CO2 and CH4 into syngas and higher hydrocarbons. In this study, DRM was investigated using Ag–Ni/Al2O3 packing and Sn–Ni/Al2O3 packing in a parallel plate dielectric barrier discharge (DBD) reactor. The performance of the DBD reactor was significantly enhanced when applying Ag–Ni/Al2O3 and Sn–Ni/Al2O3 due to the relatively high electrical conductivity of Ag and Sn as well as their anti-coke performances. Using Ag–Ni/Al2O3 consisting of 1.5 wt% Ag and 5 wt% Ni/Al2O3 as the catalyst in the DBD reactor, 19% CH4 conversion, 21% CO2 conversion, 60% H2 selectivity, 81% CO selectivity, energy efficiency of 7.9% and 0.74% (by mole) coke formation were achieved. In addition, using Sn–Ni/Al2O3, consisting of 0.5 wt% Sn and 5 wt% Ni/Al2O3, 15% CH4 conversion, 19% CO2 conversion, 64% H2 selectivity, 70% CO selectivity, energy efficiency of 6.0%, and 2.1% (by mole) coke formation were achieved. Sn enhanced the reactant conversions and energy efficiency, and resulted in a reduction in coke formation; these results are comparable to that achieved when using the noble metal Ag. The decrease in the formation of coke could be correlated to the increase in the CO selectivity of the catalyst. Good dispersion of the secondary metals on Ni was found to be an important factor for the observed increases in the catalyst surface area and catalytic activities. Furthermore, the stability of the catalytic reactions was investigated for 1800 min over the 0.5 wt% Ag-5 wt% Ni/Al2O3 and 0.5 wt% Sn-5 wt% Ni/Al2O3 catalysts. The results showed an increase in the reactant conversions with an increase in the reaction time.

Photothermal synergy for efficient dry reforming of CH4 by an Ag/AgBr/CsPbBr3 composite

Dry reforming of CH4 by photothermal catalysis is considered to be a promising approach to produce syngas.

A review on recent advances in dry reforming of methane over Ni- and Co-based nanocatalysts

The recent environmental-related issues such as climate change and global warming have sparked scientists' interest in finding a way to reduce the emission of greenhouse gases through dry reforming of CH4. As a result of this reaction, not only H2 is produced, but also CO2 and CH4 are reduced. Catalysts are needed due to the enhancement of the kinetics of the reaction. Non-noble metals like Ni, Co, etc., have shown promising activity, they are readily available, and have low cost; consequently, they have been widely employed for the reaction. In this paper, the recent advances in the development of the Ni- and Co-based nanocatalysts for DRM reaction, including the use of different supports and promoters, the addition of alkaline earth metals, and new structures like mesoporous silica and dendritic fibrous nano silica as supports were reviewed.

Active Exsolved Metal-Oxide Interfaces in Porous Single-Crystalline Ceria Monoliths for Efficient and Durable CH4 /CO2 Reforming.

Dry reforming of CH4 /CO2 provides an attractive route to convert greenhouse gas into syngas; however, the resistance to sintering and coking of catalyst remains a fundamental challenge at high operation temperatures. Here we create active and durable metal-oxide interfaces in porous single-crystalline (PSC) CeO2 monoliths with in situ exsolved single-crystalline (SC) Ni particles and show efficient dry reforming of CH4 /CO2 at temperatures as low as 450 °C. We show the excellent and durable performance with ≈20 % of CH4 conversion and ≈30 % of CO2 conversion even in a continuous operation of 240 hours. The well-defined active metal-oxide interfaces, created by exsolving SC Ni nanoparticles from PSC Nix Ce1-x O2 to anchor them on PSC CeO2 scaffolds, prevent nanoparticle sintering and enhance the coking resistance due to the stronger metal-support interactions. Our work would enable an industrially and economically viable path for carbon reclamation, and the technique of creating active and durable metal-oxide interfaces in PSC monoliths could lead to stable catalyst designs for many challenging reactions.

Carbon deposition behaviors in dry reforming of CH4 at elevated pressures over Ni/MoCeZr/MgAl2O4-MgO catalysts

Carbon deposition is a major bottleneck for the development of durable catalysts applicable for the dry reforming of CH4 (DRM). In this work, the carbon deposition behaviors in dry reforming of CH4 at elevated pressures over Ni/MoCeZr/MgAl2O4-MgO catalysts which exhibited a durable stability and excellent coking resistance at atmospheric pressure DRM reaction in our previous report were examined. The differences in the types and sources of carbon deposition under atmospheric pressure and elevated pressure were clarified by XRD, TPO, TEM and Raman spectroscopy as well as the comparative experiments conducted in CH4, CO and CH4/CO atmospheres. It was found that the stability of the catalyst declined rapidly at elevated reaction pressure, and the sources and types of carbon deposition in DRM reaction under atmospheric pressure and pressurized conditions were significantly different at temperatures above 800 °C, but barely differed at temperatures below 700 °C. Under atmospheric pressure, the filamentous carbon (carbon nanotubes, CNTs) was produced by CH4 decomposition reaction and CO disproportionation reaction at 500 and 600 °C, the encapsulated graphitic carbon was generated by CH4 decomposition reaction at 800 and 850 °C, and the filamentous carbon and encapsulated graphitic carbon deriving from CH4 decomposition reaction and CO disproportionation reaction coexisted at 700 °C. Under high pressure, CH4 decomposition reaction and CO disproportionation reaction were jointly involved in the formation of carbon deposition. The filamentous carbon was formed regardless of the reaction temperature, and accompanied by the encapsulated graphitic carbon at 700, 800 and 850 °C. It is concluded that stable DRM catalysts at atmospheric pressure may not be competent for the pressurized DRM because the sources and types of carbon deposition at pressurized conditions are different and the methods of carbon removal and suppression at atmospheric pressure are not fully applicable, thus further study is needed to develop durable catalysts at pressurized DRM.

Numerical modeling and mechanism investigation of nanosecond-pulsed DBD plasma-catalytic CH4 dry reforming

Plasma-catalytic CH4 dry reforming is an emerging technology that takes advantage of plasma-catalysis interactions to implement the conversion of CH4 and CO2 into syngas and valuable chemicals. In this work, an experiment is conducted to determine the reduced electric field E/N in the numerical modeling. In addition to essential reactor parameters, catalysis characteristics are integrated into the modeling. The 3D geometry of a nanosecond (ns) pulsed DBD plasma reactor for plasma-catalytic CH4 dry reforming is reduced into a 0D kinetics model to investigate the inherent plasma-catalysis mechanisms. The simulation results indicate that C2O4 + and CH4 +, H and O, and CH4(v 13) are the dominant ions, radicals and vibrationally excited species, respectively. Although the reactions related to CH4 and CO2 consume 19.7% and 80.3% of the total electron energy, the electron energy loss caused by the CH4 ionizations (1.3%) is distinctly higher than that caused by the CO2 ionizations (0.4%). Surface reactions can generate a large amount of adsorbed species CH3(s), H(s), CO(s) and O(s). An amount of 77.2% of formaldehyde is produced by the reaction between CH3 and O. In addition, methanol is derived from the reactions between CH3 and OH in the pulsed dielectric barrier discharge (DBD) plasma catalytic reforming CH4/CO2. This numerical modeling reflects the practical plasma-catalysis system and therefore should be a novel tool to further understand the complicated underlying mechanism of the ns-pulsed DBD plasma-catalytic CH4 dry reforming.

Plasma chemical conversion of methane by pulsed electron beams and non-self-sustained discharges

Investigations of methane conversion in atmospheric-pressure mixtures of various composition and temperature, irradiated by pulsed nanosecond electron beams and non-self-sustained discharges initiated by electron beams, were carried out. It was shown that during direct conversion at room temperature, the energy cost of the conversion of one CH4 molecule (5.6 eV molecule−1) was commensurate with that obtained in the experiments with the use of continuous electron beam. The main products of direct conversion were hydrogen and ethylene. If a small amount of oxygen was present in the mixture, methanol was added to the conversion products, which in turn decomposed into CO, CO2 and H2O. The results of numerical simulations and experiments were basically the same. The use of a non-self-sustained discharge increased the degree of direct conversion of methane, but the energy cost of conversion also increased. The main products of carbon dioxide conversion of CH4 (dry reforming) under the action of pulsed electron beam at room temperature were CO, H2, C2H6, and carbon. Energy cost of conversion (12 eV molecule−1) was about two times higher than in the case of direct conversion of methane. However, the use of pulsed electron beam for dry reforming turned out to be energetically more efficient than the use of the most types of discharges. The main products of CH4 oxidative conversion by pulsed electron beam were H2, C2H6, and C2H4. At room temperature, the energy cost of methane conversion without a catalyst was 9 eV molecule−1, whereas the use of Ni catalyst resulted in a seven-fold increase, and the use of NaOH/CaO one—in a 14-fold increase in the conversion efficiency compared to irradiation without a catalyst. When the temperature of the catalysts rised to 623 K, the conversion efficiency increased by another four times. The processes in electron-beam plasma that provide the implementation of the main mechanisms of methane conversion are also discussed in the paper.

Dry Reforming of CH4 /CO2 by Stable Ni Nanocrystals on Porous Single-Crystalline MgO Monoliths at Reduced Temperature.

Dry reforming of CH4 /CO2 provides a promising and economically feasible route for the large-scale carbon fixation; however, the coking and sintering of catalysts remain a fundamental challenge. Here we stabilize single-crystalline Ni nanoparticles at the surface of porous single-crystalline MgO monoliths and show the quantitative production of syngas from dry reforming of CH4 /CO2 . We show the complete conversion of CH4 /CO2 even only at 700 °C with excellent performance durability after a continuous operation of 500 hours. The well-defined and catalytically active Ni-MgO interfaces facilitate the reforming reaction and enhance the coking resistance. Our findings would enable an industrially and economically viable path for carbon reclamation, and the "Nanocrystal On Porous Single-crystalline Monoliths" technique could lead to stable catalyst designs for many challenging reactions.

Inhibitor, co-catalyst, or intermetallic promoter? Probing the sulfur-tolerance of MoOx surface decoration on Ni/SiO2 during methane dry reforming

As for the application of CH4dry reforming(DRM), primary concern was focused on solving the deactivation ofsupported Ni catalystscaused byparticle sintering and coke accumulation, while little attention has been paid to negative effect resulted from sulfur poisoning. The present work gave an account of the effect of H2S on the DRM over MoOx decorated Ni/SiO2 catalyst. It showed that Mo modified samples presented better sulfur resistance performance. Moreover, the interesting discovery was that different forms of Mo species were worked as special roles during H2S-induced DRM. The suitable amount of Mo, involved as the inhibitor and/or the co-catalyst, could increase the competitive adsorption capacity for H2S, thus slowing down sulfuration rate of the active Ni sites. Meanwhile, as for the specially pre-reduced catalysts, the formed intermetallic metal of Ni-Mo component contributed to a continuous sulfur-adsorption behavior for H2S, thus protecting the active Ni sites from sulfuration. Consequently, probing the sulfur-tolerance of MoOxsurface decoration on Ni/SiO2could elucidate some useful keys for the development of high sulfur-resistance catalysts, which, as a consequence, would be adequate catalysts for the H2S-induced DRM process.

Scenario assessment for producing methanol through carbon capture and utilization technologies considering regional characteristics

Carbon capture and utilization (CCU) technology can be used to reduce carbon dioxide (CO2) emissions and mitigate climate change. CCU technology efficiencies and regional characteristics were evaluated by integrating process simulation and carbon footprint estimation to determine the optimal social implementation scenarios from the CO2 emissions reduction perspective. Methanol (MeOH) was chosen as the CCU product, and the energy efficiency of MeOH synthesis under various conditions was assessed. For social implementation scenarios, location of each technology, capacity of renewable energy and H2 manufacturing method, process configuration, CO2 source, and separation/recovery technology were used as conditions for the evaluation. Based on 11 cases with varying conditions, the partial oxidation and dry reforming of CH4 was determined to exhibit the greatest CO2 emission reduction potential. However, when considering renewable energy expansion, direct MeOH synthesis exhibited a greater CO2 reduction potential. Based on the results, CCU optimal social implementation scenarios evaluation guidelines were determined. These guidelines can be implemented at a large scale to determine the viability and effectiveness of CCU technologies.

A novel catalytic reaction system capturing solid carbon from greenhouse gas, combined with dry reforming of methane

Technologies for the recovery of carbon from greenhouse gases such as carbon dioxide and methane in the solid state will lead to the development of a low-carbon society. For the purpose of realizing such technology, we constructed a catalytic reaction system that continuously captures solid carbon while producing synthesis gas by dry reforming of CH4 (DRM). The constructed reaction system exhibited high DRM activity without catalyst deterioration, with a maximum rate of 20.3% for capturing solid carbon. The use of an iron-based wall-type catalyst and the control of the capturing temperature were effective in improving the carbon capturing rate. We have succeeded in developing a novel catalytic reaction system that can collect solid carbon at a much lower temperature than that by methane decomposition. It was considered that carbon deposition from synthesis gas proceeds via a reaction mechanism which includes formation of cementite (Fe3C). The quality of the collected carbon varied depending on the capturing conditions. In particular, it was confirmed that carbon subjected to higher temperatures contained carbon-nanotubes (CNTs) with high crystallinity and elongation.

Dry reforming of CH4 over NiCo/Ce0.75Zr0.25O2-δ: The effect of Co on the site activity and carbon pathways studied by transient techniques

The effects of cobalt in the CeZrO2-supported NiCo (3 wt%, Co/ :Ni=3/2) on the DRM at 750oC were investigated by the transient method and use of 18O2 and 13CO2. Transient kinetic rates of carbon deposition and gasification by the support’s oxygen, TOF (s-1) and concentration of active carbon were determined. Higher TOF and reduced carbon accumulation rates were measured on NiCo than Ni at the initial stage of reaction. However, oxidation of Co with time-on-stream led to lower and higher concentration of active metal sites and deposited carbon, respectively. These results appear important for catalyst design improvements (e.g. metal alloy composition).

The effects of fuel variability on the electrical performance and durability of a solid oxide fuel cell operating on biohythane

Biohythane is typically composed of 60/30/10 vol% CH4/CO2/H2 and can be produced via two-stage anaerobic digestion of renewable and low carbon biomass with much greater efficiency compared with CH4/CO2 biogas. This work investigates the effects of fuel variability on the electrical performance and fuel processing of a commercially available anode supported solid oxide fuel cell (SOFC) operating on biohythane mixtures at 750 °C. Cell electrical performance was characterised using current-voltage curves and electrochemical impedance spectroscopy. Fuel processing was characterised using quadrupole mass spectroscopy. It is shown that when H2/CO2 is blended with CH4 to make biohythane, the SOFC efficiency is significantly increased, high SOFC durability is achieved, and there are considerable savings in CH4 consumption. Enhanced electrical performance was due to the additional presence of H2 and promotion of CH4 dry reforming, the reverse Boudouard and reverse water-gas shift reactions. These processes alleviated carbon deposition and promoted electrochemical oxidation of H2 as the primary power production pathway. Substituting 50 vol% CH4 with 25/75 vol% H2/CO2 was shown to increase cell power output by 81.6% at 0.8 V compared with pure CH4. This corresponded to a 3.4-fold increase in the overall energy conversion efficiency and a 72% decrease in CH4 consumption. A 260 h durability test demonstrated very high cell durability when operating on a typical 60/30/10 vol% CH4/CO2/H2 biohythane mixture under high fuel utilisation due to inhibition of carbon deposition. Overall, this work suggests that decarbonising gas grids by substituting natural gas with renewably produced H2/CO2 mixtures (rather than pure H2 derived from fossil fuels), and utilising in SOFC technology, gives considerable gains in energy conversion efficiency and carbon emissions savings.

Coke-resistant Y2O3-promoted cobalt supported on mesoporous alumina for enhanced hydrogen production

In this work, the δ%Y–10%Co/MA (δ = 0, 1, 2, 3, and 5 wt%) catalysts synthesised by sequential incipient wetness impregnation were characterised and evaluated in CH4 dry reforming. Superior catalytic performances were shown by 3 wt% Y2O3 loading (CH4 conversion = 85.8%, and CO2 conversion = 90.5%), followed by 2 wt% > 5 wt% > 1 wt% > 0 wt% Y2O3 loading. This result was attributed to the favorable catalytic properties of 3 wt%Y–10%Co/MA including small Co particle size, high Co dispersion, high amount of atomic ratio (Co/Al), and high number of lattice oxygen vacancies. The excess Y2O3 addition (>3 wt%) led to inevitably blocked Co active sites and resulted in decreasing catalytic performance. The 3 wt% Y2O3 promoter loading recorded the lowest carbon deposited (7.0%) due to the highest oxygen vacancies (78.1%) compared to 1, 2 and 5 wt% Y2O3.

Efficient dry reforming of methane with carbon dioxide reaction on Ni@Y2O3 nanofibers anti-carbon deposition catalyst prepared by electrospinning-hydrothermal method

Dry reforming of CH4 with CO2 is an effective way to convert these two greenhouse gases into useful industrial feedstock. Here, we designed and developed Ni@Y2O3 nanofibers catalyst by pyrolyzing sheet-like Ni2(CO3) (OH)2 grown in situ on the surface of Y2O3 nanofibers. Y2O3 nanofibers support can not only promote the contact of the reaction gas with the catalyst due to its self-supporting effect, but also improve the ability to capture CO2 because of its basic oxide properties. Meanwhile, the oxygen exchange between the catalyst and CO2 could promote the oxidation of carbon deposits, and further improve activity and stability of the catalyst. Besides, the catalyst obtained by low-temperature pyrolysis could maintain the sheet-structure of nickel on the surface of support, which is conducive to improve its catalytic activity, stability, and resistance to carbon deposition. This work has a positive effect on improving the design of catalysts as well as producing industrial chemicals and reducing the environmental pollution.

Catalytic Performance of Metal Oxides Promoted Nickel Catalysts Supported on Mesoporous γ-Alumina in Dry Reforming of Methane

Dry reforming of CH4 was conducted over promoted Ni catalysts, supported on mesoporous gamma-alumina. The Ni catalysts were promoted by various metal oxides (CuO, ZnO, Ga2O3, or Gd2O3) and were synthesized by the incipient wetness impregnation method. The influence of the promoters on the catalyst stability, coke deposition, and H2/CO mole ratio was investigated. Stability tests were carried out for 460 min. The H2 yield was 87% over 5Ni+1Gd/Al, while the CH4 and CO2 conversions were found to decrease in the following order: 5Ni+1Gd/Al &gt; 5Ni+1Ga/Al &gt; 5Ni+1Zn/Al &gt; 5Ni/Al &gt; 5Ni+1Cu/Al. The high catalytic performance of 5Ni+1Gd/Al, 5Ni+1Ga/Al, and 5Ni+1Zn/Al was found to be closely related to their contents of NiO species, which interacted moderately and strongly with the support, whereas free NiO in 5Ni+1Cu/Al made it catalytically inactive, even than 5Ni/Al. The 5Ni+1Gd/Al catalyst showed the highest CH4 conversion of 83% with H2/CO mole ratio of ~1.0.

Catalytic activity of SBA-15 supported Ni catalyst in CH4 dry reforming: Effect of Al, Zr, and Ti co-impregnation and Al incorporation to SBA-15

In this study, the catalytic activity of the mesoporous SBA-15 supported Ni–Al, Ni–Zr, and Ni–Ti catalysts prepared by an impregnation method were investigated in dry reforming of methane. In addition, Al incorporated SBA-15 (Al–SBA-15) materials used as catalyst support were synthesized following a one-pot hydrothermal route in three different conditions: synthesis in the presence of only HCl, only NaCl, and both HCl and NaCl (denoted as A, S, and B, respectively). All catalysts were characterized by XRD, N2 adsorption-desorption isotherms, ICP-OES, DRIFTS, SEM, TEM-EDX and TGA techniques before and/or after reaction tests. Among Al, Zr, and Ti impregnated catalysts, Ni–Al impregnated catalyst showed the highest activity in dry reforming of methane. According to activity test results, Al–SBA-15 supported Ni catalyst prepared by the one-pot hydrothermal route in the presence of both HCl and NaCl showed the best catalytic activity with high methane (81%) and carbon dioxide conversion (88%) values at 750 °C. The highest H2 and CO selectivity values were obtained with the same catalyst with an H2/CO molar ratio of 0.80. Therefore, these results showed that partial Al (0.11%) incorporated into the structure of SBA-15 was sufficient to improve the catalytic activity of the catalyst in dry reforming of methane.

Effect of Pressure on Na0.5La0.5Ni0.3Al0.7O2.5 Perovskite Catalyst for Dry Reforming of CH4

In this paper, a comprehensive study was carried out on the application of perovskite catalyst in dry reforming of CH4. The perovskite catalyst was prepared using a sol–gel method. The prepared samples were characterized by N2 adsorption/desorption, TPR, XRD, CO2-TPD, TGA, TPO, Raman, and SEM techniques. In addition, the effect of operating pressure, namely, 1 bar, 3 bar, 5 bar, and 7 bar, temperature (500–800 °C) was evaluated. The characterization results indicated that catalysts operated at 1 bar, gas hourly space velocity of 84000 (mL/g/h) gave the best catalytic performance. CH4 and CO2 conversions of 77 and 80% were obtained at 1 bar and at 700 °C reaction temperature. The increase of reaction temperatures from 500 °C to 800 °C increased the reaction rate and hence the methane and carbon dioxide conversions were increased. A unity ratio of H2/CO was obtained at 1 bar for temperatures 600 °C and above. Similarly, the time on stream tests, obtained at a 700 °C reaction temperature, showed that the best ratio in terms of the closeness of unity and the stable profile could be attained when the pressure was set to 1 bar. The TGA analysis showed the drop of mass due to oxidation of carbon deposits, which started at 500 °C. The catalyst operated at 1 bar produced the least amount of carbon, equivalent to 35% weight loss, while the 3 and 5 bar operated catalysts generated carbon formation, equivalent to 65% weight loss. However, the 7 bar operated catalyst resulted the highest accumulation of carbon formation, equivalent to 83% weight reduction. Hence, the TGA profile indicated the relative carbon deposition on the catalyst, which was dependent of the operated pressure and hence confirmed the suitability operation pressure of 1 bar. The characterizations of the Raman, EDX, TGA, and TPO all presented the formation of carbon.

Highly efficient methane decomposition to H2 and CO2 reduction to CO via redox looping of Ca2FexAl2-xO5 supported NiyFe3-yO4 nanoparticles

Catalytic methane decomposition (CMD) due to its various potentials including production of COx free H2 and technically simpleness, but is very challenging due to the lack of efficient, stable, and carbon-separable catalysts. An innovative chemical looping methane decomposition with CO2 reduction (CLMDCR) was developed to bridge the gap via the reduction → CMD → oxidation looping of a catalytic oxygen carrier (COC) for H2 production, deposited carbon separation, and CO2 reduction to CO. As high as 96.3 vol.% and 95.2 vol.% purities of H2 and CO can be generated using the COC (NiyFe3-yO4-Ca2FexAl2-xO5), superior to those obtained with state-of-the-art CH4 dry reforming. The COC shows not only high activities but also remarkable durability as demonstrated with 20 cyclic CLMDCR tests. Experimental results indicate that the long-term redox durability of COC is attributed to its atomic homogenization through the phase transformations of NiyFe3-yO4 ↔ Ni-Fe and Ca2Fe1.52Al0.48O5 ↔ CaO + Fe + Ca2FexAl2-xO5.