Multiple Redox Cycles Research Articles

Effect of Cu doping on morphology and properties of calcium ferrite and its application as oxygen carrier in chemical looping hydrogen production

Chemical looping hydrogen production with inherent CO2 capture has been widely recognized as a clean and efficient approach to high-purity hydrogen production because of the ultra-pure H2 product without any purification facilities. It is crucial to develop oxygen carriers with better performance to improve fuel conversion and hydrogen production efficiency. The potential of Ca2Fe2O5 in steam converting has been confirmed. However, its lower oxygen transfer capacity, that is, it tends to produce lower fuel conversion in fuel reactors, which will limit its practical application. Here, we report the development of Cu-doped Ca2Fe2O5-based oxygen carriers using sol-gel technology. The effects of B-site substitution of Cu element on the morphological properties and redox properties of Ca2Fe2-xCuxO5 (x = 0, 0.1, 0.25, 0.5, 1) oxygen carriers were evaluated based on experiments and density functional theory calculations. The results show that Cu doping not only elevated the surface oxygen content and enhanced the oxygen activity of the oxygen carriers, but also increased the Fe3+ at the B-site, thus enhanced their binding ability with oxygen molecules. Vacancy formation was a rate-determining step in the chemical looping hydrogen production (CLH), and Cu-doped Ca2Fe2O5 reduced the energy of oxygen vacancy formation. In the CLH process, the doping of Cu significantly improved the hydrogen productivity and fuel conversion rate. The fuel conversion rate was positively correlated with the doping amount of Cu. When x = 1, Ca2Fe2-xCuxO5 had the maximum fuel conversion rate, and its average conversion was 54.2% more than that of undoped Ca2Fe2O5. Ca2Fe2-xCuxO5 with x = 0.25 was the most suitable for CLH with the highest H2 yield, which was 20.3% more than that of Ca2Fe2O5. Moreover, its properties remained stable over multiple redox cycles with high activity and stability for CO-CLH.

Regulating cobalt-nitrogen function centers via Cu incorporation enhances ciprofloxacin destruction through peroxymonosulfate activation

Metal-nitrogen (M-N) coupling has shown promise as a catalytic active component for various reactions. However, the regulation of heterogeneous catalytic materials with M-N coupling for peroxymonosulfate (PMS) activation to enhance the degradation efficiency and reusability of antibiotics remains a challenge. In this study, an efficient modulation of M-N coupling was achieved through the incorporation of Cu into Co4N to form a Cu-Co4N composite with sea urchin-like morphology assembled by numerous nano-needles using hydrothermal and nitriding processes. This modulation led to enhanced PMS activation for ciprofloxacin (CIP) degradation. The Cu-Co4N/PMS system demonstrated exceptional removal efficiency with a degradation rate of 95.85% within 30 min and can be reused for five time without obvious loss of its initial activity. Additionally, the catalyst displayed a high capacity for degrading various challenging organic pollutants, as well as remarkable stability, resistance to interferences, and adaptability to pH changes. The synergistic effect between Co and Cu facilitated multiple redox cycles, resulting in the generation of reactive oxidized species. The primary active species involved in the catalytic degradation process included 1O2, SO4•-, O2•-, •OH, and e−, with 1O2 and SO4•- playing the most significant roles. The degradation pathways and toxicity of the intermediates for CIP were unveiled. This study offers valuable insights into the regulation of M-N centers for degrading antibiotics through PMS activation.

Enhanced hydrogen production of Fe-based spinel by relay catalysis of Fe0 and Fe-Ov-Cr species in chemical looping H2O splitting

Chemical looping H2O splitting is considered as a promising approach to produce hydrogen thanks to its lower energy consumption and carbon footprint compared with traditional steam reforming. Fe-based oxides have been paid much attention but suffer from inferior H2 production rate and stability due to insufficient activation for H2O. Herein, it was found that the introduction of Cr into MgFe spinel oxides (MgFexCr2-xO4, MFCO) could greatly increase the performance of H2O splitting driven by CH4 reduction with the highest peak H2 production rate of about 4.65 mmol min−1 g−1, H2 productivity of about 2.88 mmol g−1 and good stability during multiple redox cycles for MFCO-46 (the atomic ratio of Fe and Cr of 2:3), which exceeded most of the state-of-the-art Fe-based oxides. This originated from the Cr doping promoting Fe0 nanoparticles exsolution by activating CH4 and Fe-Ov-Cr species formation which relay catalyzed H2O splitting and was favorable for the fast recovery of lattice oxygen converted.

Investigation of AFeO3 (A=Ba, Sr) Perovskites for the Oxidative Dehydrogenation of Light Alkanes under Chemical Looping Conditions.

Oxidative dehydrogenation (ODH) of light alkanes to produce C2-C3 olefins is a promising alternative to conventional steam cracking. Perovskite oxides are emerging as efficient catalysts for this process due to their unique properties such as high oxygen storage capacity (OSC), reversible redox behavior, and tunability. Here, we explore AFeO3 (A=Ba, Sr) bulk perovskites for the ODH of ethane and propane under chemical looping conditions (CL-ODH). The higher OSC and oxygen mobility of SrFeO3 perovskite contributed to its higher activity but lower olefin selectivity than its Ba counterpart. However, SrFeO3 perovskite is superior in terms of cyclic stability over multiple redox cycles. Transformations of the perovskite to reduced phases including brownmillerite A2Fe2O5 were identified by X-ray diffraction (XRD) as a cause of performance degradation, which was fully reversible upon air regeneration. A pre-desorption step was utilized to selectively tune the amount of lattice oxygen as a function of temperature and dwell time to enhance olefin selectivity while suppressing CO2 formation from the deep oxidation of propane. Overall, SrFeO3 exhibits promising potential for the CL-ODH of light alkanes, and optimization through surface and structural modifications may further engineer well-regulated lattice oxygen for maximizing olefin yield.

Design a novel Ca-Mn perovskite oxygen carrier with balanced performance in chemical looping combustion

The cornerstone of chemical looping combustion (CLC) is oxygen carriers (OCs), and most OCs have one or more ever-present problems with performance, cost, stability, and service life. It is vital to develop OCs with balanced performance. A novel CM0.625TF-Mg OC is proposed in this study via B-site elemental substitution of CaMnO3 perovskite. Systematic experiments using a thermogravimetric analyzer (TGA), a batch fluidized bed reactor, a fixed bed reactor, and an air jet attrition apparatus are performed to evaluate various aspects of the performance of the OC manufactured by the hydraulic molding method. First, in isothermal TGA redox cycles, CM0.625TF-Mg OC exhibits a high oxygen donation ratio (∼5.0 wt.%) and excellent cyclic stability. Mg substitution eliminates the activation effect and promotes lattice oxygen release. Then, the CH4-fueled CLC experiments on a batch fluidized bed demonstrate that Mg B-site substitution promotes oxygen uncoupling (0.2 wt.% gaseous oxygen) and significantly improves its reactivity with CH4. Following that, an agglomeration resistance test on a packed bed reveals that CM0.625TF-Mg OC particles expand slightly yet exhibit remarkable agglomeration resistance. Further characterization results from SEM, EDS, and XRD analysis show that the perovskite phase is formed in fresh CM0.625TF-Mg OC via solid-phase synthesis at 1350 °C, and OC has high thermal and chemical stability during the multiple redox cycles. According to the attrition test results, CM0.625TF-Mg OC has an 8333-hour service life. Last, CM0.625TF-Mg OC has a material cost of $0.892/kg and a use cost of 0.00217 ($/kg[O]/h). In summary, this CM0.625TF-Mg OC has excellent and balanced performance in reactivity, stability, agglomeration resistance, attrition resistance, and cost, which is of great value for industrial demonstration of CLC in the later stage.

Syngas production through multi-cycle chemical looping of chromite mines waste: A sustainable approach to mitigate CO2 emissions

One of the major contributors to global warming is the CO2 emissions from the steel industry. In the primary steel making process, coal/coke is used for reduction purposes that lead to CO2 emissions. Replacing coke with other reducing agents like syngas (H2 and CO) could be a possible approach to reduce CO2 emissions. One effective route for the generation of syngas in a sustainable way is the chemical looping method. In this work, we have investigated the utilization of laterite ore (a mining waste) as an Oxygen carrier for the chemical looping reforming of methane. Multiple redox cycles in the presence of methane and air as reducing and oxidizing agents were performed in DSC-TG to determine the performance of the oxygen carrier. The reacted samples formed in the reaction were analyzed using XRD and SEM. The product gases generated during the reaction were also analyzed using gas chromatography. The results of the reactivity analysis showed that H2 and CO gases were continuously formed during the reforming reaction of methane. The phase analysis of reacted samples in XRD and SEM clearly showed the formation of stable chromite and reduced iron oxide phases. The oxygen carrier showed good stability, and a total hydrogen yield of 203.9 ml/g of OC after 20 cycles of redox reaction were observed. In addition, the theoretical yield of the reacted sample after the first cycle was calculated and compared with the experimental H2 yield at different cycles. A thermodynamic-based simulation study is also reported in this work. The syngas generated from the reforming reaction is used to pre-reduce the Iron bearing ore materials in a blast furnace. The results showed a significant decrease in the CO2 emissions and coke rate could be achieved in primary steelmaking by integrating a chemical looping process with a blast furnace. This study effectively shows the utilization of laterite ore as an oxygen carrier for generating syngas through a chemical looping reforming process to mitigate CO2 emissions.

Optimizing performance of iron-rich sludge ash as cost-effective oxygen carrier by calcium-based additive for syngas production from biomass chemical-looping gasification

Chemical-looping gasification tests were conducted on pine sawdust using thermogravimetric analyzer and horizontal sliding resistance furnace to investigate the regulation effects of calcium-based additive on iron-rich sludge ash oxygen carrier. The impacts of temperature, CaO/C in mole, multiple redox cycles, CaO addition modes on gasification performances were analyzed. The TGA results indicated that the CaO addition could effectively capture CO2 from syngas to from CaCO3, which subsequently decomposed at high temperatures. From in-situ CaO addition experiments, the temperature rise resulted in higher syngas yields, while a decrease in syngas LHV. With the CaO/C growing, the H2 yield grew from 0.103 to 0.256Nm3/kg at 800.0℃, and the CO yield boosted from 0.158 to 0.317Nm3/kg. Multiple redox manifested that the SA oxygen carrier and calcium-based additive kept higher reaction stability. The possible reaction mechanisms showed that the syngas variations from BCLG were influenced by the calcium roles and valence change of iron.

Enhancement of iron‐based oxygen carriers through alloying with tungsten oxide for chemical looping applications including water splitting

AbstractChemical looping applications offer a variety of options to decarbonise different industrial sectors, such as iron and steel and hydrogen production. Chemical looping with water splitting (CLWS) is a chemical looping technology, which produces H2 while simultaneously capturing CO2. The selection of oxygen carriers (OCs) available to be used in CLWS is finite, due to the thermodynamic limitations of the oxidation with steam for different materials at the relevant process temperatures. Iron‐based materials are one of the most widely studied options for chemical looping combustion (CLC), touted for their relative abundance and low cost; likewise, for CLWS, iron is the most promising option. However, when the reduction of iron oxide (Fe2O3) is extended to wüstite (FeO) and iron (Fe), agglomeration and sintering problems are the main challenge for fluidisation.This work presents iron and tungsten mixed oxides as the OCs for a family of chemical looping applications. The OCs were produced via co‐precipitation; performance assessment was conducted in a thermogravimetric analyser and a lab‐scale fluidised bed reactor over continuous redox cycles. The use of tungsten combined with iron results in a solid solution of tungsten within the Fe2O3 matrix that produced a more mechanically stable material during operation, which performed well during multiple redox cycles with no apparent decrease in the oxygen transport capacity and showed no apparent agglomeration. Furthermore, materials containing tungsten showed a resistance to carbon deposition, whereas the reference Fe2O3 showed peaks of CO and CO2 during the oxidation period, thus indicating carbon deposition. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Fe-based oxygen carrier for the chemical looping combustion of CO, H2, and CH4 syngas in fluidized bed reactor under interruption of H2S

Chemical looping combustion (CLC) reduces the CO2 capturing cost, elevates combustion efficiency, and prevents NOx formation. This study applied Fe2O3/SiO2 and Fe2O3/Al2O3 oxygen carriers to react with H2, CO and CH4 under different operating setup and examined the interference of H2S. Examination was also conducted on the reaction kinetics, cycle test, and characterization of oxygen carriers. Reduction of oxygen carrier from Fe2O3 to between FeO and Fe occurred during the reaction. The higher syngas concentration led to higher diffusion capacity and promoted utilization of oxygen carriers. Carbon deposition was enhanced by excess concentration of CO and CH4. Involvement of H2S led to declining of performance due to the presence of carbonyl sulfide (COS) and FeS. With Fe2O3/SiO2, application of multiple redox cycles reduced the utilization value to 43 % due to formation of Fe2SiO4. Analysis of exhausted gas after reaction was applied in study of proposed reaction mechanism. Study of reaction kinetics using Type I deactivation test indicated a well fitted result with experimental data with R2 in the range of 0.9605–0.9976. Thus, compared to other studies with discussion only on CO, H2, or CH4 in CLC, this study offered a comprehensive research on interruption of H2S, characterization, and reaction kinetics.

The Realization of complete carbon conversion and hydrogen purification in the coal-fueled chemical looping technology using a cost-effective iron-based oxygen carrier

The development of cost-effective and reactive oxygen carriers and the fast and complete conversion of solid fuels are two critical issues in the solid fuel chemical looping technology. Red mud, a solid waste from the alumina industry, was found to be an economic oxygen carrier candidate simultaneously realizing the use of solid wastes and the CO2 abatement after comparing with other two different iron-based materials (pure Fe2O3 and hematite). This study validated red mud as an excellent oxygen carrier to achieve the almost complete conversion of char in solid fuels (SFs) (99.4%) and meanwhile the hydrogen production with high-purity (97% H2 purity) and higher H2 yield (around 500 mL/g), in the optimized pyrolysis procedure of solid fuels with proper gasification agent and rationalized reaction temperatures (1000 °C) and residence time (10mins). Characterizations of red mud using SEM-EDS and XRD revealed that the unique microscopic crystalline structures of both Fe2O3 and Ca2Al2SiO7 particles nested on Na4Al2Si2O9 molten substrate, implying that the existence of Na-containing component of the red mud OC likely accounts for its higher reactivity and stability in multiple redox cycles.

Migration of lattice oxygen during chemical looping dry reforming of methane with Ca2Fe2O5/Zr0.5Ce0.5O2 oxygen carrier

Ca2Fe2O5/Zr0.5Ce0.5O2 exhibits excellent reactivity in chemical looping dry reforming of methane. The migration of lattice oxygen is crucial to the cyclic stability of oxygen carrier, but the lattice oxygen migration in Ca2Fe2O5/Zr0.5Ce0.5O2 were not extensively explored. This work explored the lattice oxygen migration of Ca2Fe2O5/Zr0.5Ce0.5O2 during redox process. During the reduction process, the lattice oxygen reacted with the hydrogen radical, resulting in the decrease of lattice oxygen content and the increase of oxygen vacancy. As the lattice oxygen released, the spatial structure of Ca2Fe2O5 was destroyed and transferred into Fe8Ca8O20 with oxygen defects due to lattice distortion. The exothermic reaction between H2 and Ca2Fe2O5 promoted the formation of FeH with hexagonal close-packed structure. After reduction for 160 min, the unstable FeH completely converted into FeC with stable structure and the complete reduction was reached. As for the oxidation process, Fe and CaO reacted with the oxygen radical to form Ca2Fe2O5, leading to the complete recovery of lattice oxygen within 40 min. However, crystalline phase transformation could lead to the spatial structure instability and sintering after multiple redox cycles. Overall, the migration of oxygen during redox process is clarified in detail, providing a reference for improving the cyclic stability of Ca2Fe2O5/Zr0.5Ce0.5O2.

Hydrotalcite-Derived Copper-Based Oxygen Carrier Materials for Efficient Chemical-Looping Combustion of Solid Fuels with CO2 Capture.

Chemical-looping combustion (CLC) is a promising technology that utilizes metal oxides as oxygen carriers for the combustion of fossil fuels to CO2 and H2O, with CO2 readily sequestrated after the condensation of steam. Thermally stable and reactive metal oxides are desirable as oxygen carrier materials for the CLC processes. Here, we report the performance of Cu-based mixed oxides derived from hydrotalcite (also known as layered double hydroxides) precursors as oxygen carriers for the combustion of solid fuels. Two types of CLC processes were demonstrated, including chemical looping oxygen uncoupling (CLOU) and in situ gasification (iG-CLC) in the presence of steam. The Cu-based oxygen carriers showed high performance for the combustion of two solid fuels (a lignite and a bituminous coal), maintaining high thermal stability, fast reaction kinetics, and reversible oxygen release and storage over multiple redox cycles. Slight deactivation and sintering of the oxygen carrier occurred after redox cycles at an very high operation temperature of 985 °C. We expect that our material design strategy will inspire the development of better oxygen carrier materials for a variety of chemical looping processes for the clean conversion of fossil fuels with efficient CO2 capture.

Effect of alkali earth metal doping on the CuO/Al2O3 oxygen carrier agglomeration resistance during chemical looping combustion

The influence of alkali earth metals (AEMs, including Ca, Sr and Ba) doping on the performance of CuO/Al2O3 oxygen carrier (OC) in chemical looping combustion (CLC) was investigated. The OCs using solid-state synthesis method were evaluated in a fluidized bed reactor using municipal solid waste (MSW) syngas as fuel for 50 redox cycles. It was found that the doping of AEMs enhanced the CLC performance on CuO/Al2O3. XRD characterization and TGA analysis showed that aluminates of AEMs were formed in the doped OCs leading to the segregation of CuO from CuAl2O4 spinel, thereby promoting the redox kinetics. The OCs doped with AEMs exhibited enhanced stability and agglomeration resistance throughout multiple redox cycles in the fluidized bed experiments. CuO/Al2O3 containing 40 wt% CuO suffered from severe agglomeration and deactivation during initial 5 cycles, while the OCs with Ba, Sr and Ca doping respectively deferred the agglomeration to 15-20th, 20-25th and >50th cycle. 5–10 wt% Ca-doping content exhibited great stability without deactivation or agglomeration issues during 50 cycles, but excess Ca doping (≥20 wt%) showed severe agglomeration. The agglomeration was attributed to the outward migration of Cu/CuO, leading to the segregation from CuAl2O4 and surface enrichment. The enhanced agglomeration resistance with AEM doping was mainly attributed to outward migration of AEM species and inward migration of Cu species during the synthesis process.

Synergistic effect of Ce-Mn on cyclic redox reactivity of pyrite cinder for chemical looping process

Pyrite cinder (Pc) is a solid waste from sulfuric acid production. The cleaner and efficient utilization of pyrite cinder is of great significance to achieve the recycling of industrial solid waste. In this study, we prepared different doped pyrite cinder-based oxygen carriers (Ce-Pc, Ce-Mn-Pc, Mn-Pc), and investigated the synergistic effect of Ce-Mn on cyclic redox reactivity of pyrite cinder in chemical looping process. The synergy between Ce and Mn in the modified pyrite cinder for fuel combustion reactivity was discussed in detail. The addition of Mn enhanced the cyclic stability of CeO2-doped pyrite cinder during sequential chemical looping cycles. The synergistic effect of Ce-Mn facilitated the generation of oxygen vacancies, which improved the mobility of lattice oxygen and enhanced the reducibility. The results indicated that the effect of CeO2 and MnOx on the cyclic redox reactivity of pyrite cinder was relatively weak compared with the synergistic effect of CeO2-MnOx. In addition, Ce-Mn could prevent grain growth and agglomeration of pyrite cinder. After the 20th cycle, the oxygen carrying capacity (OCC) of raw pyrite cinder decreased significantly from 3.63% in the 1st cycle to 2.45%. During the multiple redox cycles, the Ce-Mn-Pc presented the highest OCC (about 3.6%). The Ce-Mn co-doped pyrite cinder presented excellent cyclic durability with CH4 conversion more than 85% during successive cycles. This study provides an approach for the rational design of pyrite cinder-based oxygen carriers with high cyclic redox reactivity and durability.

Atomic-scale platinum deposition on photocathodes by multiple redox cycles under illumination for enhanced solar-to-hydrogen energy conversion

The fabrication of photoelectrochemical (PEC) cells using Cu2O, a semiconductor light absorber that responds to infinite sunlight, requires techniques for loading and activating highly efficient cocatalysts to increase the hydrogen production selectivity. However, there has been relatively little interest in techniques for the deposition of efficient catalysts on PEC electrodes that can maximize the surface activation of the light absorption layer for water splitting, because precise control of the Pt loading at the atomic scale is difficult. We designed an intelligent multiple-redox illuminated deposition technique capable of depositing atomic-scale Pt catalysts with optimal performance on the photocathode surface. An Sb:Cu2O/Cu2O/Al:ZnO/TiO2 photocathode with the proposed atomic-scale Pt catalyst has a high photocurrent density of 6.2 mA cm−2 and a more positive onset potential of 0.71 VRHE. In addition, the mass activity of this electrode is 3.35 times higher than that of Pt samples deposited by conventional methods, and the electrode also shows outstanding operational stability. The proposed approach enables a uniform catalyst distribution and position-selective deposition atomic-scale Pt by repeated redox reactions. Consequently, our proposal enables the simultaneous realization of enhanced conversion efficiency and low cost by the consumption of a relatively small quantity of Pt in controllable redox photodeposition.

A novel hydrogen peroxide fluorescent probe for bioimaging detection and enables multiple redox cycles

In this subject, a novel hydrogen peroxide (H2O2) fluorescent probe (MNG) was designed and developed using naphthalimide derivatives and selenomorpholine. In PBS buffer (10 mM, pH = 7.4, 1 %DMSO), the selenomorpholine on the probe is capable of qualitatively and quantitatively detecting (H2O2) at a small amount under a detection limit of 61 nM. The probe follows a mechanism that Se (Ⅱ) in selenomorpholine is transformed to Se (Ⅳ), thus changing the spectra of the probe MNG. It is noteworthy that MNG can continuously make a cyclic response to H2O2 and glutathione (GSH), so it can potentially achieve redox process imaging in vivo. Moreover, this subject verified the redox process of the probe’s continuous redox response in the Gaussian 09 programme through simulation calculation and mass spectrometry. The probe exhibits high biocompatibility. Moreover, it can detect H2O2 in MCF-7 cells and Argentine Bloodfin.

Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO) and other munitions constituents by wood-derived biochar through its rechargeable electron storage capacity.

The environmental fate of 3-nitro-1,2,4-triazol-5-one (NTO) and other insensitive munitions constituents (MCs) is of significant concern due to their high water solubility and mobility relative to legacy MCs. Plant-based biochars have been shown to possess a considerable electron storage capacity (ESC), which enables them to undergo reversible electron transfer reactions. We hypothesized biochar can act as a rechargeable electron donor to effect abiotic reduction of MCs repeatedly through its ESC. To test this hypothesis, MC reduction experiments were performed using wood-derived biochars that were oxidized with dissolved oxygen or reduced with dithionite. Removal of aqueous NTO, an anion at circumneutral pH, by oxidized biochar was minimal and occurred through reversible adsorption. In contrast, NTO removal by reduced biochar was much more pronounced and occurred predominantly through reduction, with concomitant formation of 3-amino-1,2,4-triazol-5-one (ATO). Mass balance and electron recovery with ferricyanide further showed that (1) the amount of NTO reduced to ATO was relatively constant (85-100 μmol per gram of biochar) at pH 6-10; (2) the fraction of biochar ESC reactive toward NTO was ca. 30% of that toward ferricyanide; (3) the NTO-reactive fraction of the ESC was regenerable over multiple redox cycles. We also evaluated biochar transformation of other MCs, including nitroguanidine (NQ), 2,4-dinitroanisole (DNAN), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). While mass and electron balances could not be established due to sorption, DNAN and RDX reduction by reduced biochar was confirmed via detection of multiple reduction products. In contrast, NQ was not reduced under any of the conditions tested. This study is the first demonstration of organic contaminant degradation through biochar's rechargeable ESC. Our results indicate biochar is a regenerable electron storage medium and sorbent that can remove MCs from water through concurrent reduction and sorption, and is thus potentially useful for pollution control and remediation at military facilities.

Selenium mobility in a major Chalk aquifer (Lille metropolis, northern France): Contaminants cycles driven by geology, redox processes and pumping

Chalk groundwater in northern France presents selenium (Se) concentrations from <10 to 70 μg L−1, partly exceeding the latest European Framework Directive's drinking-water limit value of 20 μg L−1. Better to understand the heterogeneous dynamics of Se, we used a combination of geochemical, isotopic and geophysical tools on a study site belonging to the Metropolis of Lille, France. This approach provided a fine understanding of the Se fate in a dynamic redox system constrained by geology, related redox processes and pumping, illustrating how local versus global controls affect the Se cycling. A remarkable redox sequence controls element transfers in groundwater with a progressive creation of reductive conditions. Highlighted by geophysical tools, a wide fracture corridor in the Chalk formation disrupts the geological setting of this redox sequence. Under pumping, this corridor allows the mixing of oxygenated groundwater with groundwater under reducing conditions. The evolution of isotopic compositions of sulphate molecules confirms the global reduction trend of sulphates, while pyrite oxidation occurs very locally, together with high Se concentrations. Pyrite is expected to play a predominant role in Se mobility in the Chalk aquifer. Se and other redox sensitive elements (Fe, Mn, N and S) undergo multiple redox cycles, resulting in a Se-rich redox front that migrates downward over time within the water-level fluctuation zone of the porous Chalk. With the decreasing trend of water levels caused by global changes, a Se stock could be immobilized in the unsaturated zone, but nitrate content and redox conditions in the saturated zone will be major drivers for Se mobility.

Binary-ore oxygen carriers prepared by extrusion–spheronization method for chemical looping combustion of coal

In this study, composite oxygen carriers (OCs) were prepared by the extrusion–spheronization method, using disused fine (<100 μm) iron and copper ores as raw materials. A range of inert aluminosilicates (namely diatomite, montmorillonite, rectorite, pseudo-boehmite, pumice, and attapulgite) were tested as binders to achieve uniform physical mixing of iron ore and copper ore powders in a single OC particle, one-step particle shaping, and synergistic effect between active components. Firstly, the extrusion-spheronization process was optimized to achieve a sufficient crushing strength. It was found that FeCu-10 M (72 wt% iron ore, 18 wt% copper ore, and 10 wt% montmorillonite added as a binder) and FeCu-5P (76 wt% iron ore, 19 wt% copper ore, and 5 wt% pumice) OCs showed a relatively high crushing strength (greater than 2 N). Subsequently, the coal chemical looping combustion performance tests were conducted in a batch-fluidized bed. FeCu-10 M performed better at a bed temperature of 950 °C and for an oxygen-to-fuel ratio of 2.5 to 3.1. The OC also demonstrated excellent reactivity and stability during multiple redox cycles. The X-ray diffraction (XRD) pattern revealed that no obvious interphase side reaction occurred among different components within the particles. Scanning electron microscopy (SEM) characterization indicated no obvious sintering within the particle or agglomeration between the particles. The experimental results demonstrated that the extrusion–spheronization method is suitable for large-scale preparation of OC particles. The binary-ore OCs prepared by extrusion–spheronization exhibited good performance in terms of reactivity, stability, and economy.

Thermochemical hydrogen production using Rh/CeO2/γ-Al2O3 catalyst by steam reforming of ethanol and water splitting in a packed bed reactor

This study is focused on investigating the dual performance of Rh/CeO2/γ-Al2O3 catalyst for steam reforming of ethanol (SRE) and thermochemical water splitting (TCWS) using a packed bed reactor. The catalyst is designed to be thermally stable containing an active phase of Rh and the redox component of CeO2 for oxygen exchange, supported on γ-Al2O3. The catalyst has been characterised by SEM, XRD, BET, TPR, TPD, XPS and TGA before testing in the reactor. The optimal temperature for SRE reaction over this catalyst is between 700 °C and 800 °C to produce high concentrations of hydrogen (~60%), and low CO and CH4. The selectivity towards CO and CH4 is higher at low temperatures and drops with rise in reaction temperature. Further, Rh/CeO2/γ-Al2O3 is found to be active for TCWS at relatively low temperatures (≤1200 °C). At temperatures as low as 800 °C, this catalyst is especially found suitable for multiple redox cycles, producing a total of 48.9 mmol/gcat in four redox cycles. The catalyst can be employed for large number of redox cycles when the reactor is operated at lower temperatures. Finally, the reaction pathways have been proposed for both SRE and TCWS on Rh/CeO2/γ-Al2O3 catalyst.