Number Of Redox Cycles Research Articles

Antiviral Effects of Pyrroloquinoline Quinone through Redox Catalysis To Prevent Coronavirus Infection.

The global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) coronavirus disease (COVID-19) is ongoing. Therefore, effective prevention of virus infection is required. Pyrroloquinoline quinone (PQQ), a natural compound found in various foods and human breast milk, plays a role in various physiological processes and is associated with health benefits. In this study, we aimed to determine the effects of PQQ on preventing coronavirus infections using a proxy Feline Infectious Peritonitis Virus (FIPV; belongs to the coronavirus family). In plaque reduction assays, we showed that pre- and post-PQQ-treated viruses were less infectious. IC50 was 87.9 and 5.1 μM for pre- and post-PQQ-treated viral infections, respectively. These results suggest that PQQ decreased the virion stability and viral replication. RT-qPCR confirmed these results. TEM findings showed that PQQ damaged viral capsids and aggregated viral particles, leading to inhibited virus attachment and entry into the host cells. PQQ was optimized by the addition of ascorbic acid and glutamic acid, which increased the number of redox cycles of PQQ and increased reactive oxygen species production by 14 times. In vitro, PQQ inhibited 3 CLpro/Mpro enzymes (an enzyme critical for viral replication) activity of SARS-CoV-2. Our results demonstrate the antiviral effect of PQQ on coronavirus, mainly by disrupting virion stability and loss of infectivity (occurring outside the host cell), due to increased redox activity. Furthermore, PQQ may hinder viral replication (inside the host cell) by 3 CLpro/Mpro enzyme inhibition. In summary, this study demonstrates the antiviral effect of PQQ and its potential application in coronavirus diseases.

Sintering and agglomeration characteristics of industrially prepared CaMn0.5Ti0.375Fe0.125O3-δ perovskite oxygen carrier in chemical looping combustion

The development of oxygen carrier particles that can be prepared on an industrial scale with good cycling stability remains a challenge in the field of chemical looping. In this work, a perovskite oxygen carrier (CaMn0.5Ti0.375Fe0.125O3-δ) was prepared by an industrial-scale spray drying granulation and tested on a fluidized bed thermogravimetric analyzer for long-term chemical looping combustion. The results showed that the attrition of oxygen carrier particles originated from irregular parts of the fresh particle surface early in the cycle, and the chemical stress on particles gradually increased with the number of redox cycles, increasing the attrition and sintering of the particles. In addition, as the cycle proceeds, the perovskite structure was destroyed and the oxygen carrier reacted chemically with the quartz tube wall and the air distribution plate leading to bonding. The deep redox cycling reactions indicated that agglomeration of particles occurred mainly in the reduction stage, with the bed entering repeated periods of defluidization during the 37th-43rd and 47th-55th cycles due to the changes in particle bonding and bed pressure. Fixed bed experiment showed that particle activation came from an increase in the active area of the particles during the cycle, independent of whether they were fluidized or not. In addition, agglomeration started at the contact surface between the air distribution plate and the particles, resulting in blocked oxidation of the particles and deepening agglomeration due to excessive reduction of the particles.

Interfacial effect on the polarization resistance of SrM0.1Mo0.9O3-δ (M = Mg2+, Fe3+)/GDC-based composite electrodes

The present study examines the interfacial effect on the area-specific resistance (ASR) offered by SrM0.1Mo0.9O3-δ (M = Mg2+, Fe3+)/Gd0.1Ce0.9O2-δ (GDC) composite electrodes. The symmetrical cells having 8YSZ electrolyte and SrFe0.1Mo0.9O3-δ/Gd0.1Ce0.9O2-δ composite electrodes are fabricated with and without the GDC buffer layer. The electrode ASR in cells with and without GDC-buffer layer is 0.09 Ω.cm2 and 0.68 Ω.cm2 at 850 °C in 3% H2O/H2, respectively. More than a 50% rise in the magnitude of electrode ASR is seen in cells with no GDC buffer layer after 10 redox cycles. Phase analysis of these cells reveals a dense layer of an insulating SrZrO3-based phase formed at the electrode/electrolyte interface due to the chemical reaction between SrFe0.1Mo0.9O3-δ and 8YSZ. In contrast, the cells possessing a GDC buffer layer show a small ASR increase from 0.09 Ω.cm2 to 0.14 Ω.cm2 after the same number of redox cycles without the presence of any secondary phase. The effect of the current collector contact area on the ASR of the SrMg0.1Mo0.9O3-δ/Gd0.1Ce0.9O2-δ composite electrode is also evaluated. Symmetrical cells with a dense GDC buffer layer and composite electrodes are prepared. The Pt current collector area on the electrode layer is varied from 0.13 cm2 to 0.5 cm2, and the electrode specific resistance is measured at 850 °C in a 3% H2O/H2 environment. The electrode resistance declines with increasing current collector area. The cell with the electrode surface entirely covered by the current collector exhibits a very low ASR of ∼ 0.07 Ω.cm2. The sensitivity of the interfacial polarization resistance towards a slight change in the strength of the current field is the possible reason for observing such ASR variation.

CuxMn1-xFe2O4 as oxygen carrier for chemical looping steam methane reforming

The spinel-ferrite structure (SFS) oxygen carrier (OC) CuxMn1-xFe2O4 with (x = 0.3, 0.5, 0.6, and 0.7) was synthesized by the co-precipitation technique to be used in the chemical looping steam methane reforming process (CL-SMRP). The SFS OCs were characterized using Fourier Transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDX), Thermogravimetric Analysis (TGA), and Brunauer-Emmett-Teller (BET). The Response Surface Methodology (RSM) based on the Box-Behnken model was employed to estimate the effects of independent variables and their interactions on the OC activity. The effects of temperature, OC, loading percentage, steam to methane molar ratio, the number of redox cycles on the H2 production yield (YH2), methane conversion(XCH4), and SCO/CO2 were determined. According to the analysis of variance (ANOVA) analysis, results indicated that the reaction temperature and the OC (x) have extremely significant effects on XCH4 and YH2. The maximum XCH4 of 98.7%, YH2of 81.02%, and SCO/CO2 of 6.54 were obtained at optimal value conditions such as 650 °C, SFS OC Cu0.6Mn0.4Fe2O4, S/C 2.5, and redox cycle 30.

Role of Copper Migration in Nanoscale Ageing of Supported CuO/Al2O3 in Redox Conditions: A Combined Multiscale X‐ray and Electron Microscopy Study

AbstractChemical Looping Combustion is a promising midterm solution to mitigate CO2 emission, by carrying out indirect fuel combustion and allowing inherent separation of CO2. During the CLC process, an oxygen carrying material is subjected to successive oxidation‐reduction reactions at high temperature which induce significant material degradation. CuO/Al2O3 based materials have been widely considered as promising oxygen carriers (OC). However, the oxygen carrier ageing mechanisms (active phase migration and interactions with the support, phase transitions) are not well understood. Herein, an in‐depth overview of the material evolution is achieved by employing a multi‐scale characterization approach. At the μm‐scale, copper migration within the alumina support has been observed using Scanning Transmission X‐ray Microscopy (STXM) and Scanning Electron Microscopy (SEM). The spatial distribution of the Cu−Al species provides information on copper mobility and the different phases interactions. A comprehensive mechanism is proposed concerning the redox behaviour of the CuO/Al2O3 system, relating the diffusion of the Cu‐species, the active phase‐support interactions, and the role of copper in the Al2O3 support phase transition to the temperature and the number of redox cycles. Understanding the ageing process of CuO/Al2O3 materials paves a way to design more stable oxygen‐carriers.

Estimation of microscale redox tolerance for Ni-based solid oxide fuel cell anodes via three-dimensional finite element modeling

Reduction-oxidation (redox) cycles of Ni-based anodes in solid oxide fuel cells (SOFCs) directly affect the cell performance due to breaking anode three/triple phase boundary (TPB) networks at microscale. Furthermore, these microcracks accumulate with the number of redox cycles leading to mechanical damage in the cell as a result of continuous volumetric changes during the inevitable cyclic reduction and oxidation of the nickel oxide and nickel, threatening the service life of SOFC systems. Therefore, the redox process needs to be investigated as a phenomenon at microscale to understand and minimize its effects. In this regard, we suggest a microscale approach for the redox process of Ni-based SOFC anodes in this study. For this purpose, SOFC anode microstructures with different compositions and porosities are synthetically generated by Dream.3D software and mechanical damages due to the redox cycle are investigated via element deletion through LS-DYNA for the first time in the literature. The anodes are characterized by computing the redox tolerance based on the resultant damage and the anode composition showing the highest redox tolerance is determined among the cases considered.

Investigation into support effects for Pt and Pd on LaMnO3

The catalytic properties of Pt and Pd supported on thin-film LaMnO3 were investigated. The LaMnO3 film consisted of an ALD-grown 0.5-nm-thick film supported on a high-surface-area MgAl2O4. Pt and Pd were added to the LaMnO3 films by Atomic Layer Deposition (ALD) and then aged by repeated oxidation and reduction cycles at 1073 K. X-Ray Diffraction (XRD), together with Scanning Transmission Electron Microscopy (STEM)/Energy Dispersive Spectroscopy (EDS) showed that Pt underwent extensive sintering during these redox treatments and formed a Pt-Mn alloy following reduction at 1073 K. Consistent with this, the activity of the supported Pt catalysts for CO oxidation decreased progressively with the number of redox cycles. In contrast to the results for Pt, STEM/EDS results indicated that Pd remained well dispersed on LaMnO3, even after five redox cycles. The Pd catalyst showed high activity for CO oxidation at lower temperatures due to a low activation energy and positive reaction order in CO. XRD results with Rietveld analysis for the Pd catalyst indicated the presence of very large crystallites for PdO on the oxidized catalyst and metallic Pd on the reduced catalyst, inconsistent with the high dispersions measured by STEM and the high CO-oxidation rates. Possible explanations for these observations are discussed.

Relationship between microstructure and deformation of porous Ni-based cermets under redox cycling

This paper discusses the relationship between the elongation and compression behavior and microstructural changes under redox cycles of porous Ni(O)–YSZ cermets for solid oxide fuel cells (SOFC). Mechanical damage in SOFC and SOEC is one of the most important degradation factors governing the electrical performance of cells. Therefore, it is necessary to know the mechanical properties of each component material, such as elastic and deformation properties, in the operating environment. Particularly, of the Ni(O)–YSZ cermets which currently makes up 90% of the volume of the cell, with present mainstream anode supported SOFC and SOEC. Therefore, understanding the properties of the Ni(O)–YSZ cermets plays an important role in ensuring the performance of the entire SOFC and SOEC. In this study, the microstructural changes of Ni(O)–YSZ cermet by reduction, re-oxidation and re-reduction were observed in detail using microstructural observations and systematically compared with the dimensional change behavior. For the dimensional change behavior, a simple model considering the initial porosity and Ni content is proposed, which successfully predicts the dimensional change due to re-oxidation. Furthermore, Ni(O)–YSZ cermets with high Ni content show large initial dimensional changes, but the dimensional reversibility improves with increase of the number of redox cycles.

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.

A precise polyrotaxane synthesizer.

Mechanically interlocked molecules are likely candidates for the design and synthesis of artificial molecular machines. Although polyrotaxanes have already found niche applications in exotic materials with specialized mechanical properties, efficient synthetic protocols to produce them with precise numbers of rings encircling their polymer dumbbells are still lacking. We report the assembly line-like emergence of poly[n]rotaxanes with increasingly higher energies by harnessing artificial molecular pumps to deliver rings in pairs by cyclical redox-driven processes. This programmable strategy leads to the precise incorporation of two, four, six, eight, and 10 rings carrying 8+, 16+, 24+, 32+, and 40+ charges, respectively, onto hexacationic polymer dumbbells. This strategy depends precisely on the number of redox cycles applied chemically or electrochemically, in both stepwise and one-pot manners.

Attrition of ilmenite ore during consecutive redox cycles in chemical looping combustion

Chemical looping combustion divides combustion into separate reduction and oxidation (redox) reactions that are linked via a particulate oxygen carrier. The resistance of the oxygen carrier to attrition is an important factor that affects its lifetime. Here, we examined the effects of consecutive redox cycles and degrees of reduction on the attrition of ilmenite ore. First, samples were prepared by subjecting ilmenite to 0 to 150 redox cycles in a fluidized-bed reactor. Next, the resistance of the samples to attrition was examined in a laboratory-scale fluidized bed at room temperature. The attrition rate increased with the number of redox cycles, particularly between 50 and 100 redox cycles, and degree of reduction. Observations of the samples via scanning electron microscopy and measurements of their tapped density and reduction rate revealed that the rapid increase was the result of surface morphological changes, including migration of iron toward the particle surfaces.

Redox stability of metal-supported fuel cells with nickel/gadolinium-doped ceria anode

Metal-supported fuel cells (MSCs) are promising candidates for not only stationary but also mobile applications. Their appeal is in their potential to withstand reoxidation of the anode, which might occur by an interruption of the fuel supply or an emergency shutdown of the fuel cell system. A novel nickel/gadolinium-doped ceria anode (Ni/GDC) was recently introduced in a MSC concept of Plansee, almost doubling power density compared to cells with a nickel/yttria-doped zirconia (Ni/YSZ) anode. In this study, both cell concepts are compared concerning their ability to tolerate harsh redox cycles. Therefore, controlled redox cycles of the anodes were conducted at different temperatures. The response of the cell's power output to the redox cycling experiments was continuously recorded. In the case of MSCs with a Ni/YSZ anode, strong degradation occurs after redox cycling. In contrast, cells with a Ni/GDC anode exhibit significantly improved redox tolerance and cell performance improves with the number of redox cycles. For understanding this behavior, microstructural investigations of the Ni/GDC anode and the adjacent electrolyte were performed by FIB-SEM. The long-term redox behavior of MSCs with a Ni/GDC anode was also investigated by conducting more comprehensive redox cycles at 400 °C, 500 °C, and 600 °C.

Insights into the relationship between microstructural evolution and deactivation of Al2O3 supported Fe2O3 oxygen carrier in chemical looping combustion

The Fe2O3-Al2O3 oxygen carrier is regarded to a promising candidate for chemical looping combustion (CLC). However, Fe2O3-Al2O3 oxygen carrier was often subjected to a decrease of oxygen carrying capacity. The deactivation mechanism of Fe2O3-Al2O3 oxygen carrier in chemical looping combustion was investigated over consecutive 20 cycles. The Fe2O3-Al2O3 oxygen carrier exhibited relatively poor redox stability in a fixed bed reactor. The physico-chemical properties of cycled Fe2O3-Al2O3 oxygen carrier were characterized by different characterization methods. No carbon deposit was detected in the reduction process, indicating that carbon deposition was not the cause for Fe2O3-Al2O3 oxygen carrier deactivation under this experimental condition. The characterization results showed that the deactivation of Fe2O3-Al2O3 oxygen carrier in redox cycles was mainly attributed to thermal sintering. The cycled Fe2O3-Al2O3 oxygen carrier showed lower surface area, lower reducibility and oxygen mobility than that of fresh sample. After a certain number of redox cycles, Fe diffusion and enrichment at the surface of cycled oxygen carrier was observed. The surface Fe is unstable under high reaction temperature, leading to accelerate thermal sintering. A deactivation mechanism of Fe2O3-Al2O3 oxygen carrier in CLC was proposed based on the Fe diffusion and surface sintering.

Perovskite Sr(Fe1-xCux)O3-δ materials for chemical looping combustion applications

This paper presents the results of chemical looping combustion (CLC) research. Nowadays, CLC is one of the best prospective combustion technologies, because it enables the production of a concentrated carbon dioxide (CO2) stream, following water condensation, without any energy penalty for its separation.The objective of this work was to study chemical looping reaction performance with the application of novel perovskite-type oxygen carriers (OCs). Sr(Fe1-xCux)O3-δ family members were tested for hydrogen combustion for power generation purposes. Sr(Fe1-xCux)O3-δ, which is a perovskite-type oxide, was prepared using the calcination method, where x = 0, 0.1 and 0.33. Reactivity tests were performed using a thermogravimetric analyser (TGA, Netzsch STA 409 PG Luxx) under isothermal conditions in multiple reduction–oxidation cycles. Both the temperature (600–800 °C) and number of redox cycles (five cycles) effects on the reaction performance of recently developed OC samples were evaluated in the study. TGA data were used for the assessment of the oxygen transport capacity value, redox reaction rates and stability. Sr(Fe1-xCux)O3-δ showed an excellent stable chemical looping performance. The changing of oxygen content (3.8–4.86 wt%) occurred within approximately 2 min, with the chemical properties of the material maintained during the cycling combustion tests.In addition, new SrFeO3-δ OCs, doped with copper (Cu) perovskite-type materials, were analysed using multiple methods: X-ray powder diffraction (XRD); scanning electron microscopy (SEM); surface area by Brunauer–Emmett–Teller (BET) method; and melting behaviour study. In terms of physical properties, the new OCs can resist both high CLC process temperatures and mechanical forces, which are essentially useful. The analysis showed that Sr(Fe1-xCux)O3-δ carriers performed at extremely high melting temperatures (>1280 °C). Results of crushing strength testing showed that developed materials had a pronounced mechanical resistivity with a crushing strength higher than 1 N and will perform well in fluidized beds (4.31–6.23 N).In this paper, it was demonstrated that known mixed oxygen-ionic and electronic conducting membrane materials such as Sr(Fe1-xCux)O3-δ might also be applied as oxygen carriers. Overall results demonstrated Fe-Cu-based perovskites might be successfully used as OCs in the chemical looping combustion process.

Copper-based oxygen carriers supported with alumina/lime for the chemical looping conversion of gaseous fuels

Copper (II) oxide in varying ratios was combined with either an alumina-based cement (Al300), or CaO derived from limestone as support material in a mechanical pelletiser. This production method was used to investigate its influence on possible mechanical and chemical improvements for oxygen carriers in chemical looping processes. These materials were tested in a lab-scale fluidised bed with CO or CH4 as a reducing gas at 950 °C. As expected, the oxygen carriers containing a greater ratio of support material exhibited an enhanced crushing strength. Oxygen carriers comprised of a 1:3 ratio of support material to active CuO exhibited increased crushing strength by a minimum of 280% compared to pure CuO pellets. All oxygen carriers exhibited a high CO conversion yield and were fully reducible from CuO to Cu. For the initial redox cycle, Al300-supported oxygen carriers showed the highest fuel and oxygen carrier conversion. The general trend observed was a decline in conversion with an increasing number of redox cycles. In the case of CaO-supported oxygen carriers, all but one of the oxygen carriers suffered agglomeration. The agglomeration was more severe in carriers with higher ratios of CuO. Oxygen carrier Cu25Al75 (75 wt% aluminate cement and 25 wt% CuO), which did not suffer from agglomeration, showed the highest attrition with a loss of approximately 8% of its initial mass over 25 redox cycles. The reducibility of the oxygen carriers was limited with CH4 in comparison to CO. CH4 conversion were 15%–25% and 50% for Cu25Ca75 (25 wt% CuO and 75 wt% CaO) and Cu25Al75, respectively. Cu25Ca75 demonstrated improved conversion, whereas Cu25Al75 exhibited a trending decrease in conversion with increasing redox cycles.

Investigation of Alternative Mixed-Conducting Oxides for SOFC Anode Applications

A testing protocol has been developed to analyse the thermal redox behavior of newly developed anode materials for SOFC application. This is in an attempt to speed through the material development process, as development of new anode materials is time consuming, labor intensive and expensive. A simple push rod type dilatometer has been used in the characterisation of high temperature redox behavior of materials by automating the timely introduction of oxidizing and reducing atmosphere in order to simulate cell stack leak. By using the present test protocol, data like co-efficient of thermal expansion (CTE), volumetric change in the cell lattice, redox behavior (volumetric expansion or volumetric reduction) and number of redox cycles before material failure can be obtained. The testing protocol has been calibrated with commonly used SOFC materials like YSZ (8 mol% yttria doped), GDC (20 mol% Gd doped), La0.35Sr0.65TiO3 (LST) and also with LST/GDC (50/50 vol%) composite.

Quantitative Analysis of Homogeneous Electrocatalytic Reactions at IDA Electrodes: The Example of [Ni(PPh2NBn2)2]2+

Interdigitated array (IDA) electrodes have been applied to study the EC’ (electron transfer reaction followed by a catalytic reaction) reactions and a new method of quantitative analysis of IDA results was developed. In this new method, currents on IDA generator and collector electrodes for an EC’ mechanism are derived from the number of redox cycles and the contribution of non-catalytic current. And the fractions of bipotential recycling species and catalytic-active species are calculated, which helps understanding the catalytic reaction mechanism. The homogeneous hydrogen evolution reaction catalyzed by [Ni(PPh2NBn2)2]2+ (where PPh2NBn2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) electrocatalyst was examined and analyzed with IDA electrodes. Besides, the existence of reaction intermediates in the catalytic cycle is inferred from the electrochemical behavior of a glassy carbon disk electrodes and carbon IDA electrodes. This quantitative analysis of IDA electrode cyclic voltammetry currents can be used as a simple and straightforward method for determining reaction mechanism in other catalytic systems as well.

In‐situ transformation of iron‐bearing minerals in marshland‐derived paddy subsoil

Transformations of Fe‐bearing minerals under alternating redox conditions are not fully understood. In‐situ approaches under field conditions have rarely been used. We exposed mesh bags containing ferrihydrite, goethite or nontronite to changing redox conditions in subsoil that had been under paddy management for 100, 700 and 2000 years. After 12 months, the minerals were retrieved and analysed for organic carbon and by X‐ray diffraction; in addition, nontronite was analysed for cation exchange capacity and by Mössbauer spectroscopy at 278 and 4.2 K. Field exposure of the test minerals was complemented by measurements of soil redox potential and analyses of soil water. Minerals accumulated little organic carbon because of high pH and salinity. Goethite samples showed no changes in X‐ray diffraction patterns; therefore, they did not undergo detectable transformation, despite redox potentials frequently around −200 mV. Ferrihydrite transformed into more crystalline oxides, such as lepidocrocite, goethite and haematite. The extent of transformation, presumably by Fe2+‐catalysed recrystallization, increased with the time the soil had been under paddy management. Nontronite samples showed striking changes in surface colour, but no changes in X‐ray diffraction patterns or in cation exchange capacity. However, Mössbauer spectroscopy gave clear indications of irreversible changes within the nontronite crystal structure. Such changes have so far been observed only with chemical reduction, but it seems that they can occur under natural conditions. The results show that the overall redox status of a soil (i.e. the number of redox cycles it has undergone before) governs the extent and direction of mineral transformations during following redox cycles.HighlightsHow do ferrihydrite, goethite and nontronite transform under strongly alternating redox conditions? In‐situ exposure of minerals in soil under paddy management for 100, 700 and 2000 years. Fe2+‐catalysed ferrihydrite transformation; irreversible changes in nontronite crystal structure. The number of redox cycles a soil undergoes, governs mineral transformations in later redox cycles.

Performance of a Victorian brown coal and iron ore during chemical looping combustion in a 10 kWth alternating fluidized bed

This paper presents the performance of Victorian Yallourn coal during chemical looping combustion with iron ore in a 10kWth alternating fluidized bed reactor. CO2 was used as the gasification agent and fluidization gas. The effect of reaction temperature, fuel type and number of redox cycles were investigated. The NOx emission from the system was determined. The used oxygen carrier particles were characterized using SEM, EDS, XRD, and surface area analyser. It was found that the optimum condition for CO2 yield and carbon conversion was obtained at a temperature of 900°C. Under this condition with the present reactor configuration, the average carbon conversion and CO2 yield over six cycles were found to be 92.2% and 82.9% respectively. Although Yallourn ash has high amounts of iron and silica, no ash deposition was detected on the oxygen carrier particles. The NOx concentration was found to be 25ppm. Results from the carbon balance showed that about 1% was present in the solid phase; about 6.8% was unaccounted for and possibly elutriated out of the reactor. While favourable results were obtained for this configuration, the use of circulating fluidized bed reactors and an improved cyclone separation system would increase the carbon conversion and CO2 yield.

Transformation of clay-sized minerals in soils exposed to prolonged regular alternation of redox conditions

The direction of the transformation of Fe-bearing minerals under harshly changing redox conditions is still under debate. Some studies suggest preferential accumulation of weakly crystalline Fe oxides while other studies showed that repeated redox cycles favour the presence of crystalline phases. Since characterized by distinct redox cycles, paddy soils are ideal for studying redox-related transformations of Fe oxides and Fe-bearing clay minerals. We analysed changes in the Fe mineral assemblage upon long-term reduction–oxidation cycles along a chronosequence of 100, 700, and 2000-year-old paddy soils developed on comparable parent material relative to two non-irrigated counterparts.The clay mineral assemblage, as indicated by X-ray diffraction, showed no significant differences between paddy and non-paddy soils as well as no changes with time under paddy management.Speciation of Fe mineral phases in top- and subsoil was accomplished by Mössbauer spectroscopy at room temperature and 4.2K, in combination with X-ray diffraction and selective chemical extractions (dithionite–citrate–bicarbonate, NH4 oxalate). We found ferrous and ferric Fe in silicates, nano- to micro-crystalline goethite and haematite, as well as a ferrihydrite-type phase. In topsoils, prolonged paddy cultivation resulted in general loss of silicate- and oxide-bound Fe in the topsoils and the remaining Fe oxide assemblage became more and more dominated by organic-rich weakly crystalline phases. Total contents of Fe oxides in subsoils increased due precipitation of Fe leached from the topsoils. Micro-crystalline goethite was the predominating Fe oxide phase in the upper subsoil, likely due to Fe2+-catalysed solid-state transformation of freshly precipitated hydrous Fe oxide phases. Lepidocrocite formed in the deeper subsoil, probably promoted by less CO2 in the soil water. Thus, paddy cultivation causes different Fe mineral weathering, forming, and transforming environments, with the depth differentiation of these environments becoming increasingly distinct with time under paddy management, i.e., the number of redox cycles the soils underwent.