Redox Loop Research Articles

Reverse Water–Gas Shift Chemical Looping Using a Core–Shell Structured Perovskite Oxygen Carrier

Reverse water–gas shift chemical looping (RWGS-CL) offers a promising means of converting the greenhouse gas of CO2 to CO because of its relatively low operating temperatures and high CO selectivity without any side product. This paper introduces a core–shell structured oxygen carrier for RWGS-CL. The prepared oxygen carrier consists of a metal oxide core and perovskite shell, which was confirmed by inductively coupled plasma mass spectroscopy (ICP-MS), XPS, and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements. The perovskite-structured shell of the prepared oxygen carrier facilitates the formation and consumption of oxygen defects in the metal oxide core during H2-CO2 redox looping cycles. As a result, amounts of CO produced per unit weight of the core–shell structured oxygen carriers were higher than that of a simple perovskite oxygen carrier. Of the metal oxide cores tested, CeO2, NiO, Co3O4, and Co3O4-NiO, La0.75Sr0.25FeO3-encapsulated Co3O4-NiO was found to be the most promising oxygen carrier for RWGS-CL, because it was most productive in terms of CO production and exhibited long-term stability.

Isothermal Splitting of CO2 to CO Using Cobalt-Ferrite Redox Looping

Abstract Rising atmospheric CO2 levels from significant imbalance between carbon emissions from fossil fuel utilization, especially for energy and chemicals, and natural carbon sequestration rates is known to drive-up the global temperatures and associated catastrophic climate changes, such as rising mean sea level, glacial melting, and extinction of ecosystems. Carbon capture and utilization techniques are necessary for transition from fossil fuel infrastructure to renewable energy resources to help delay the dangers of reaching to the point of positive feedback between carbon emissions and climate change which can drive terrestrial conditions to uninhabitable levels. CO2 captured from the atmosphere directly or from flue gases of a power plant can be recycled and transformed to CO and syngas for use as energy and value-added chemicals. Utilizing renewable energy resources to drive CO2 conversion to CO via thermochemical redox looping can provide a carbon negative renewable energy conversion pathway for sustainable energy production as well as value-added products. Substituted ferrites such as Co-ferrite, Mn-ferrite were found to be promising materials to aid the conversion of CO2 to CO at lower reduction temperatures. Furthermore, the conversion of these materials in the presence of Al2O3 provided hercynite cycling, which further lowered the reduction temperature. In this paper, Co-ferrite and Co-ferrite-alumina prepared via co-precipitation were investigated to understand their potential as oxygen carriers for CO2 conversion under isothermal redox looping. Isothermal reduction looping provided improved feasibility in redox conversion since it avoids the need for temperature swinging which improves thermal efficiency. These efforts alleviate the energy losses in heat recovery while also reducing thermal stresses on both the materials and the reactor. Lab-scale testing was carried out at 1673 K on these materials for extended periods and multiple cycles to gain insights into cyclic performance and the feasibility of sintering, which is a common issue in iron oxide-based oxygen carriers. Cobalt doping provided with lowering of reduction temperature requirement at the cost of oxidation thermodynamic spontaneity that required increased oxidation temperature. At the concentrations examined, these opposing phenomena made isothermal redox operation feasible by providing high CO yields comparable with oxygen carriers in the literature, which were operated at different temperatures for reduction and oxidation. Significantly high CO yields (∼750 µmol/g) were obtained from Co-ferrite isothermal redox looping. Co-ferrite-alumina provided lower CO yields compared with Co-ferrite. The oxygen storage was similar to those reported in the literature on isothermal H2O splitting, but with improved morphological stability at high temperature, especially compared with ferrite. This pathway of oxygen carrier development is considered suitable with further requirement in optimization for scaling of renewable CO2 conversion into valuable products.

Spatially controlled oxygen storage materials improved the syngas selectivity on chemical looping methane conversion

Chemical looping redox cycle of oxygen storage materials offers a versatile platform to convert methane to value-added products in a clean and efficient manner. However, the highly dynamic nature of the oxygen diffusion process restrains the selective formation of the target products over a long reaction period. In this work, we show the oxygen storage materials-comprising of iron oxides and zirconium oxide support, with the nickel catalyst controllably deposited—that significantly enhanced the syngas selectivity. Mechanistic study indicated the oxygen releasing rate can be well controlled within a long reaction period by the specific spatial structure, demonstrating a new strategy to tune the oxygen diffusion in chemical looping process. Through the observed spatial effects, this work can be also extended to develop more oxygen storage materials for the other chemical looping applications, e.g. methane reforming, methane oxidative coupling, ethane oxidative dehydrogenation, etc.

Effect of copper dopant on the mixed cobalt-iron oxides for hydrogen generation via chemical looping redox cycles

The long-term stability of oxygen carriers can be significantly improved by operating chemical looping at mild conditions, enabling the potential for large-scale applications. However, the diminished temperature has a detrimental effect on the kinetics, resulting in the decreased chemical looping performance. Although doping of noble metals can promote the performance of oxygen carriers at mid-temperatures, the high cost significantly impeded the scalable use of these oxygen carriers. Here we report the use of copper to dope mixed cobalt-iron oxides as oxygen carriers for hydrogen generation via chemical looping redox cycles. Cu0.25Co0.75Fe2O4 shows satisfactory hydrogen yield (~9.39 mmol g−1) and average hydrogen generation rate (~0.47 mmol g−1 min−1) with high stability over 20 redox cycles at 550 °C. The characterizations substantiate that the improved performance is a consequence of Cu to enhance the oxygen-ion conductivity through the bulk and promote the reactivity of the oxygen carriers with reactant gases on the surface. The performance of the samples in this work is comparable to those contains noble metals.

Efficient hydrogen production through the chemical looping redox cycle of YSZ supported iron oxides

The chemical looping process, where an oxygen carrier is reduced and oxidized in a cyclic manner, offers a promising option for hydrogen production through splitting water because of the much higher water splitting efficiency than solar electrocatalytic and photocatalytic process. A typical oxygen carrier has to comprise a significant amount of inert support, to maintain stability in multiple redox cycles, thereby resulting in a trade-off between the reaction reactivity and stability. Herein, we proposed the use of ion-conductive yttria-stabilized zirconia (YSZ) support Fe2O3 to prepare oxygen carriers materials. The obtained Fe2O3/YSZ composites showed high reactivity and stability. Particularly, Fe2O3/YSZ-20 (oxygen storage capacity, 24.13%) exhibited high hydrogen yield of ∼10.30 mmol g−1 and hydrogen production rate of ∼0.66 mmol g−1 min−1 which was twice as high as that of Fe2O3/Al2O3. Further, the transient pulse test indicated that active oxygen diffusion was the rate-limiting step during the redox process. The electrochemical impedance spectroscopy (EIS) measurement revealed that the YSZ support addition facilitated oxygen diffusion of materials, which contributed to the improved hydrogen production performance. The support effect obtained in this work provides a potentially efficient route for the modification of oxygen carrier materials.

Chemical looping deoxygenated gasification: An implication for efficient biomass utilization with high-quality syngas modulation and CO2 reduction

Chemical looping gasification is a promising technology for biomass utilization. However, the biomass-derived products contain tar and CO2, which seriously affects the syngas quality and hinders its development. A new approach, chemical looping deoxygenated gasification (CLDG), was proposed for high-quality, H2/CO-tunable syngas generation with CO2 utilization via redox looping of CaO + Fe ↔ Ca2Fe2O5. The CLDG process involves a deoxygenation reactor (DR) and a regeneration reactor (RR). Fe0 continuously reduces the oxygen-containing species to drive high-quality syngas production in the DR, and the oxidized oxygen carrier (Fe3+) can be reduced under CO in the RR. A thermodynamic simulation was conducted to verify the feasibility of CLDG using Aspen Plus. The effects of DR and RR temperatures, of the molar ratios of Fe/Obio, CO2/C, H2O/C, and (C + CO)/Fe on the syngas quality, H2/CO molar ratio, and the efficiency of gasification, chemical looping deoxygenation, and CO2 reduction were investigated intensively and optimized to guide the CLDG process. The results indicate that CLDG can significantly improve the quality of syngas with various H2-to-CO syngas modulations and CO2 reduction, obtaining a lower heating value (LHV) of 9.07 MJ/m3, a gasification efficiency of 96.31%, a CO2 reduction efficiency of 44.51%, an H utilization efficiency of 79.52%, and a chemical looping deoxygenation efficiency of 17.55%.

Electrochemical Detection of Curcumin in Food with a Carbon Nanotube-Carboxymethylcellulose Electrode.

Herein, an electrochemical method is presented for the detection of curcumin in food using a carbon nanotube (CNT)-carboxymethylcellulose (CMC) electrode. The CNT-CMC electrode exhibited ideal characteristics for curcumin detection, namely, a high response current and adequate peak separation toward curcumin oxidation. Cyclic voltammetry revealed two oxidation peaks. In the first scan, only the irreversible peak (Peak I) was observed at a higher potential. In the second scan, the reversible redox peak pairs (Peaks II and II') appeared at lower potentials, and the potential of Peak I was decreased. Peak I corresponded to oxidation of the hydroxyl groups of the benzene ring to the catechol group via a phenoxy radical, while Peaks II and II' indicated the redox loop system of the generated catechol group. The current at Peak II was used to quantify the concentration of curcumin in the linear range of 1 - 48 μM and detection limit of 0.084 μM. The concentrations of curcumin determined by the CNT-CMC electrode in real food samples were consistent with those determined by high-performance liquid chromatography.

Chemical looping gasification coupled with steam reforming of biomass using NiFe2O4: Kinetic analysis of DAEM-TI, thermodynamic simulation of OC redox, and a loop test

NiFe2O4 is one of the best oxygen carriers (OCs) for the biomass chemical looping gasification coupled with steam reforming. The kinetics analysis of biomass and NiFe2O4 is helpful for understanding their mechanism of interaction. In this work, a thermogravimetric analyzer, and distributed activation energy model based on a time integral (DAEM-TI) were used to study the effect of the OC/biomass ratio and atmosphere on gasification. In addition, thermodynamic analysis by Factsage and a 15-loop test of the OC in a fixed bed reactor were applied to investigate the NiFe2O4 transformation and its multiple redox performance. The kinetic analysis showed that gasification included: i) moisture loss of ~100 kJ/mol, ii) devolatilization of 150 ~ 175 kJ/mol, and iii) char gasification of 250 ~ 350 kJ/mol. There was a transition that was accompanied by a slight reduction before a rapid increment of activation energy in adjacent stages. This may be attributed to the difference between the various energy barriers of reactions. The simulation results of DAEM-TI matched the experimental data well, and all adjusted coefficients of determination exceeded 98%. The best ratio of OC/biomass was 5/5 for optimal gasification that avoided overoxidation. The mass rebound of H2O on char gasification was higher than that of CO2, which indicated H2O had stronger oxidizability than CO2. Thermodynamic simulation showed that spinel NiFe2O4 converted into an FCC Fe(Ni) alloy during gasification. However, CO2 and H2O were only capable of restoration to Fe3O4 and could not oxidize Ni to Ni2+, so calcining in air was necessary for NiFe2O4 restoration. The performance of restored NiFe2O4 remained high and even slightly improved compared to that of the fresh NiFe2O4 after 15 redox loops.

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.

A high-performance ternary ferrite-spinel material for hydrogen storage via chemical looping redox cycles

Chemical looping has been proposed as an emerging technology for large-scale hydrogen storage with the advantages of high volumetric hydrogen storage density, environmental compatibility, and safety. However, to ensure sufficient redox activity, conventional oxygen carrier materials must be operated at a temperature higher than 800 °C, leading to the rapid deterioration on the storage capacity over several cycles. In this work, we report a ternary ferrite-spinel material Cu0.5Co0.5Fe2O4 for chemical looping hydrogen storage and production. The material exhibits high volumetric hydrogen storage density (65.58 g·L−1) and average hydrogen production rate (142 μmol·g−1·min−1) at 550 °C. The performance is maintained with negligible deactivation over repetitive redox cycles. The high performance can be attributed to the ability of Cu and Co to improve the reduction and the reversible phase change during the oxidation stage at moderate temperatures. The performance of the Cu0.5Co0.5Fe2O4 is comparable to the state-of-the-art Rh-FeOx containing rare earth metals, which enables its potential in industry application.

Nano-hybrids of needle-like MnO2 on graphene oxide coupled with peroxymonosulfate for enhanced degradation of norfloxacin: A comparative study and probable degradation pathway

In this work, 1D MnO2 nano-needles were prepared and grown on the graphene oxide (GO) nano-sheets successfully. The morphology and structure of materials were explored. The MnO2 nano-needles with a length of 200–400 nm were distributed uniformly on the GO nano-sheets. As a result of GO substrate, the MnO2/GO nano-hybrids (MnO2/GO) have the much larger surface area and more surface oxygen-containing functional groups than MnO2 nano-needles, which are beneficial for enrichment and degradation of the norfloxacin (NOR). Results showed that more than 80% NOR was degraded within 20 min at the dose of 10 mM PMS and 0.8 g/L catalysts. Moreover, the optimal pH in MnO2/PMS and MnO2/GO/PMS system were both acidic condition. Furthermore, the mechanism of PMS activation by MnO2/GO was investigated through radical identification using quenching experiments and EPR techniques. According to this, the HSO5− of PMS reacted with Mn (IV)/Mn(III) to form a redox loop, and GO played an important role in the degradation process. Finally, the transformation intermediates of NOR were identified and four probable degradation pathways were speculated. This work would provide a potential contribution towards NOR removal in the environmental remediation.

OxyR Is a Convergent Target for Mutations Acquired during Adaptation to Oxidative Stress-Prone Metabolic States.

Oxidative stress is concomitant with aerobic metabolism. Thus, bacterial genomes encode elaborate mechanisms to achieve redox homeostasis. Here we report that the peroxide-sensing transcription factor, oxyR, is a common mutational target using bacterial species belonging to two genera, Escherichia coli and Vibrio natriegens, in separate growth conditions implemented during laboratory evolution. The mutations clustered in the redox active site, dimer interface, and flexible redox loop of the protein. These mutations favor the oxidized conformation of OxyR that results in constitutive expression of the genes it regulates. Independent component analysis of the transcriptome revealed that the constitutive activity of OxyR reduces DNA damage from reactive oxygen species, as inferred from the activity of the SOS response regulator LexA. This adaptation to peroxide stress came at a cost of lower growth, as revealed by calculations of proteome allocation using genome-scale models of metabolism and macromolecular expression. Further, identification of similar sequence changes in natural isolates of E. coli indicates that adaptation to oxidative stress through genetic changes in oxyR can be a common occurrence.

Time-resolved in-situ IR and DFT study: NH3 adsorption and redox cycle of acid site on vanadium-based catalysts for NO abatement via selective catalytic reduction

Transient in-situ IR spectroscopy was performed to analyze the molecular behavior of selective catalytic reduction of NO with NH3 on V2O5-WO3/TiO2 catalyst. During NH3 adsorption, an unexpected growth in the intensity of Lewis acid sites was observed due to the hydrogen migration, which was verified by the DFT calculation and the existence of intermediate species. The comparison between the isolated atmosphere experiments and the simultaneous exposure of NH3-NO-O2 on catalytic monolayer demonstrated that: (i) there exists a pathway for Lewis to Brønsted acid sites transformation at T > 300 °C, (ii) the rate determining step of the SCR cycle involves in the re-oxidation of acid sites by O2 at 200–300 °C. Generally, the Lewis acids are crucial at high temperatures, while Brønsted acids dominate the overall reaction at lower temperatures. Based on the experimental data and the DFT calculation, a mechanism for ammonia adsorption, acidity conversion and re-oxidation for the redox loop of the de-NOx reaction was proposed. The findings shed light on the understanding of relative strength of NO reduction and acid re-oxidation at different temperatures.

Reaction schemes of barium ferrite in biomass chemical looping gasification for hydrogen-enriched syngas generation via an outer-inner looping redox reaction mechanism

Abstract The objective of this study was to build an efficient outer-inner looping redox reaction mechanism called steam recycled biomass chemical looping gasification (SR-BCLG) for H2 production by using BaFe2O4 as an oxygen carrier (OC). The X-ray diffraction (XRD) results showed the phase changes of BaFe2O4 in the SR-BCLG process can be oxidized to its initial state stimulated by steam. In addition, the impacts on the temperature, water injection rate (steam/biomass ratio) and OC loading were investigated. The maximum H2 production of 28.5 mol/kg· biomass was achieved in the 60 min of gasification with a BaFe2O4 load amount of 10 wt%, which is an increase in H2 production of 109.6% compared with the no-OC biomass gasification process under the optimal conditions. Durative high production of H2-enriched syngas was obtained during the cyclic stability tests, indicating the significant redox durability and high H2-generation properties of BaFe2O4. The XRD, scanning electron microscopy (SEM), and thermo-gravimetric analyzer (TG) characterizations revealed the high stability of BaFe2O4, which can be ascribed to the existence of Ba2+. The bimetal functional BaFe2O4 allows for an innovative method of outer-inner looping redox reactions for continuous H2-enriched syngas generation in the SR-BCLG process.

Efficient purification and chemical energy recovery from urine by using a denitrifying fuel cell

Urine is a major biomass resource, and its excessive discharge would lead to severe aquatic nitrogen pollution and even eutrophication. In this study, we designed an innovative denitrifying fuel cell (DFC) under illumination to purify urine and convert its chemical energy into electricity. The central ideas include the following: 1) on the anode, chlorine radicals (Cl) and hydroxyl (HO) radicals were induced to react with amine or ammonia in urine into N2, and to mineralize organics into CO2, respectively; 2) on the cathode, NO2− or NO3− generated in the cell was selectively reduced to N2 and tiny NH4+ by Pd/Au/NF; 3) NH4+ was further oxidized to N2 by Cl according to process 1), then the total nitrogen (TN) was ultimately removed by a continuous redox loop between anode and cathode; 4) the separation and migration of charges were strengthened by a self-bias poly-Si/WO3 photoanode. Result indicated that the DFC showed an efficient yield of electricity and almost completely N-removing properties: power density of 2.24 mW cm−2, total nitrogen and total organic carbon (TOC) removal efficiency, respectively 99.02% and 50.76% for artificial urine; and power density of 2.51 mW cm−2, TN and TOC removal efficiency, respectively 98.60% and 54.55% for actual urine. The study proposes a potential and environment-friendly approach by using novel DFC to purify urine and generate electricity.

An electrogenic redox loop in sulfate reduction reveals a likely widespread mechanism of energy conservation

The bioenergetics of anaerobic metabolism frequently relies on redox loops performed by membrane complexes with substrate- and quinone-binding sites on opposite sides of the membrane. However, in sulfate respiration (a key process in the biogeochemical sulfur cycle), the substrate- and quinone-binding sites of the QrcABCD complex are periplasmic, and their role in energy conservation has not been elucidated. Here we show that the QrcABCD complex of Desulfovibrio vulgaris is electrogenic, as protons and electrons required for quinone reduction are extracted from opposite sides of the membrane, with a H+/e− ratio of 1. Although the complex does not act as a H+-pump, QrcD may include a conserved proton channel leading from the N-side to the P-side menaquinone pocket. Our work provides evidence of how energy is conserved during dissimilatory sulfate reduction, and suggests mechanisms behind the functions of related bacterial respiratory complexes in other bioenergetic contexts.

Production of CO from CO2 over mixed-metal oxides derived from layered-double-hydroxides

Carbon monoxide generation from the splitting of CO2 is of greater importance now than ever before due to continuous increase in CO2 levels in the atmosphere and concerns on the sustainability of energy and environment. This paper examines the conversion of CO2 to CO via thermochemical redox looping of metal oxides. Oxides of Mg/Fe and Mg/Al/Fe prepared from layered double hydroxide (LDH) were explored to aid in the conversion of CO2 to CO. The prepared metal oxides from LDH offered superior stability of porous metal structure and sustained redox capability at moderate to high temperatures required for conversion. The formations of these metal oxides from LDH were analyzed using thermogravimetric analysis (TGA). The results showed 635 µmol CO/g of Mg/Fe oxides as compared 557 µmol CO/g from Mg/Al/Fe. Continuous operation resulted in some sintering effects with deteriorated redox performance. The redox capability of Mg/Fe oxide over multi-cycle operations was lower as compared to Mg/Al/Fe oxides, which showed significant thermal stability while maintaining high CO yield and redox capability over extended redox cycles. The specific LDH derived metal oxides produced CO three times higher than those reported previously in the literature using Zr-doped ceria and other perovskites per unit mass of the oxygen carriers. While the surface area was reduced in Mg/Al/Fe the yield after the first cycle remained unchanged; both the surface area and yield decreased in Mg/Fe oxides. Mixed-metal oxide prepared from co-precipitation provided highly porous Mg/Al/Fe oxide compared to Mg/Fe or Mg/Al. High porosity enhanced the surface oxidation of Mg/Al/Fe that contributed to more than 85% oxidation from fast surface reactions. After two cycles, the redox rates changed little with further increase in the number of cycles to reveal surface area stability of Mg/Al/Fe. Multiple cycle operation suggested superior redox kinetics of Mg/Al/Fe than Mg/Fe. These LDH derived mixed metal (Mg/Al/Fe) oxide provided high and sustained CO production rates compared to those reported in the current literature used other materials so that the examined materials have good potential to serve as oxygen carrier for CO2 splitting to CO.

New Insight into the Development of Oxygen Carrier Materials for Chemical Looping Systems

Abstract Chemical looping combustion (CLC) and chemical looping reforming (CLR) are innovative technologies for clean and efficient hydrocarbon conversion into power, fuels, and chemicals through cyclic redox reactions. Metal oxide materials play an essential role in the chemical looping redox processes. During reduction, the oxygen carriers donate the required amount of oxygen ions for hydrocarbon conversion and product synthesis. In the oxidation step, the depleted metal oxide oxygen carriers are replenished with molecular oxygen from the air while heat is released. In recent years, there have been significant advances in oxygen carrier materials for various chemical looping applications. Among these metal oxide materials, iron-based oxygen carriers are attractive due to their high oxygen-carrying capacity, cost benefits, and versatility in applications for chemical looping reactions. Their reactivity can also be enhanced via structural design and modification. This review discusses recent advances in the development of oxygen carrier materials and the mechanisms of hydrocarbon conversion over these materials. These advances will facilitate the development of oxygen carrier materials for more efficient chemical looping technology applications.

Energy analysis of chemical looping oxidative dehydrogenation of propane

ABSTRACTFeasibility and energy analysis of chemical looping oxidative dehydrogenation of propane (CL-ODHP) process is performed by thermodynamic method. Results show that Mn2O3/MnO can be used for CL-ODHP, after one redox looping, about 100 kJ/mol energy can be generated. Energy analysis indicates that the process requires 8432.82 kJ/kgpropene external fuel input at reaction temperatures with commercial propane conversion and propene selectivity. And process energy consumption decreases with decreasing of dehydrogenation and regeneration temperatures and increasing of propane conversion and propene selectivity. Recovering waste heat of hot streams from two reactors can cut by nearly 45% energy consumption of the process.

Bifunctional Co- and Ni- ferrites for catalyst-assisted chemical looping with alcohols

Ferrite materials were applied for catalyst-assisted chemical looping with two different alcohol fuels, methanol and an ethanol-water mixture (1:1mol ratio), at 550°C and 750 °C respectively. CO2 was used for reoxidation, resulting in the production of CO. The structural characteristics, CO formation and stability of a range of x CoFe2O4/NiFe2O4 (x=20 − 100wt%) modified with CeZrO2 were investigated through STEM and in situ XRD. Crystallographic changes during two consecutive H2-TPR and CO2-TPO cycles were followed using in situ XRD. Further, the long term stability was assessed during one hundred isothermal chemical looping redox cycles using H2 for reduction and CO2 for reoxidation. The 20wt% CoFe2O4 material could be reduced and reoxidized to the as prepared state without loss in oxygen storage capacity. In 80wt% CoFe2O4 however, deactivation due to phase segregation into Co and Fe3O4 along with material sintering occurred. On the other hand, all NiFe2O4 materials modified with CeZrO2 suffered from sintering as well as phase segregation into separate Ni and Fe3O4 phases, which could not be restored into the original spinel (NiFe2O4) phase. During chemical looping with methanol, carbon formation was observed on CoFe2O4/NiFe2O4 ferrites modified with CeZrO2. 20wt% CoFe2O4 was the best performing material with a CO yield of ∼40mol CO kgCoFe2O4−1, i.e. almost twice the theoretical amount. This high CO yield was ascribed to the oxidation of carbon formed upon material reduction. During chemical looping with the ethanol-water mixture however, the CO yield remained low (∼13mol CO kgCoFe2O4−1) because of incomplete conversion of CH4 and water. A pre-catalyst bed configuration for complete conversion of CH4 and water is proposed.