Oxygen Release Rate Research Articles

Controlled chemical synthesis of CaO2 particles coated with polyethylene glycol: characterization of crystallite size and oxygen release kinetics

The oxygen release pattern of CaO2 nanoparticles was biphasic: an initial burst phase for the first 24 hours followed by a descending release rate for three days. The oxygen release rate in the second phase mainly depended on the shrinking-core model for CaO2 hydrolysis.

Lipid Microbubbles as Ultrasound-Stimulated Oxygen Carriers for Controllable Oxygen Release for Tumor Reoxygenation

Microbubbles are proposed as a potentially novel method for oxygen delivery in vivo in initial studies. The lack of commercial microbubbles for oxygen delivery in preclinical research prompted us to fabricate an oxygen-loaded lipid microbubble. We aimed to extend the innovative strategy to modulate the tumor hypoxic microenvironment, using microbubbles intravenously as an oxygen carrier for the controllable tumor-specific delivery of oxygen by ultrasound (US). In our experiment, an oxygen-loaded lipid-coated microbubble (OLM) with mixed gas (O2/C3 F8, 5:1 v/v) was fabricated and exhibited a higher rate of oxygen release to a desaturated solution through burst by US than that in the absence of US. Although in in vivo studies, OLMs could be imaged and triggered by US to elevate the pO2 level in the breast VX2 tumor dramatically within a matter of minutes. The added presence of US-activated OLMs elicited a nearly six-fold increase in pO2 levels within 1 min compared with that of the pre-injection. Owing to the high oxygen payload, great acoustic stability and acoustic properties, OLMs may be proposed as an ideal radio-sensitizer. We conclude that oxygen release mediated by ultrasound-targeted microbubble destruction is feasible and shows potential in image-guided, site-specific cancer radiotherapy.

Oxygen Storage Property and Chemical Stability of SrFe1–xTixO3−δ with Robust Perovskite Structure

The compounds of SrFe1–xTixO3−δ with a robust perovskite structure are synthesized by Ti substitution for Fe sites in SrFeO3−δ, and they display improved oxygen storage properties and chemical stability in a CO2 atmosphere. The oxygen storage rate of SrFe0.8Ti0.2O3−δ is over 5 times faster than that of SrFeO3−δ. Further, in the presence of CO2, SrFe1–xTixO3−δ with x ≥ 0.2 maintains its oxygen storage property, whereas, for x ≤ 0.1, the oxygen release rate drastically deteriorates due to the formation of SrCO3. The perovskite structures (space group I4/mmm) of SrFe1–xTixO3−δ (x ≥ 0.2) are preserved even after reduction treatment under a H2 atmosphere at 773 K. In contrast, the material with x ≤ 0.1 undergoes a phase transformation from perovskite (I4/mmm) to brownmillerite structures (Ima2), and the latter easily reacts with CO2 to form a large amount of SrCO3 on the surface. Thus, the robust perovskite structure maintains its original framework despite the reduction treatment, resulting in improved oxygen...

Evaluation of a hierarchically-structured CuO@TiO2-Al2O3 oxygen carrier for chemical looping with oxygen uncoupling

High redox reactivity as well as sufficient physical durability of the oxygen carrier (OC) is of critical importance for the successful implementation of chemical looping processes. In this work, CuO@TiO2-Al2O3 OC with hierarchical structure, which is a kind of CuO-rich, Al2O3-supported and TiO2-stablized ternary combined metal oxides system, was prepared by the self-assembly template combustion synthesis (SATCS) method. Performance of the rationally designed OC was cyclically tested with H2 in a thermogravimetric analyzer (TGA), as well as with coal in a batch fluidized bed reactor. TGA results showed that both the reduction and oxidation reactivity of the OC exhibited a reinforcing process during the first few cycles and then stabilized within the next dozens of cycles, and no obvious reactivity degradation phenomenon was observed. Reaction characteristics of the OC were further examined by reacting with coal in a fluidized bed reactor. Several critical performance indexes, like carbon conversion rate, oxygen release rate and combustion efficiency at different temperatures were calculated and compared. Mutual promotion relationship between carbon conversion rate of the coal and oxygen release rate of the OC was observed. Moreover, 20 cycles of redox process with anthracite were further conducted at 900°C to evaluate both the physical and chemical stability of the OC. Stable and high combustion efficiency (higher than 97.2%) was achieved during the cyclic fluidized bed test, and the subsequent physicochemical characterization indicated that neither CuAl2O4 phase was formed nor serious sintering problem occurred within the used OC samples. Thermo-mechanical analysis (TMA) results demonstrated relatively high transformation temperature of the OC, which explains well its superior anti-sintering property. All in all, the SATCS-derived CuO@TiO2-Al2O3 OC exhibited distinguished advantages of preventing the side reaction between CuO and Al2O3 to form copper aluminates as well as inhibiting the OC sintering, which could be a suitable OC candidate for commercial application in chemical looping with oxygen uncoupling (CLOU) processes.

Metal Oxides: Promising Materials for Electrochemical Processes

The electrochemical behavior of electrodes with an active layer comprised of TiO2, IrO2, RuO2, and SnO2 is studied. The zero-current potentials are determined. Curves of the rates of chlorine and oxygen release at the anode versus the composition of the electrode are presented.

Anchoring effect and oxygen redox property of Co/La0.7Sr0.3AlO3-δ perovskite catalyst on toluene steam reforming reaction

To elucidate specific functions of supports, we investigated steam reforming of toluene as a model compound of biomass tar over Co catalyst supported on perovskite-type oxide. Co-supported La0.7Sr0.3AlO3-δ catalyst showed the highest activity among various Co-supported catalysts. STEM measurements and XPS measurements revealed the coexistence of La cation and lattice oxygen defect produces an anchoring effect to Co particles. The lattice oxygen release rate on each catalyst was measured with H218O steady-state isotopic transient kinetic analysis (SSITKA). The anchoring effect, higher dispersion of Co and redox property, are important for the high catalytic performance of Co/La0.7Sr0.3AlO3-δ catalyst on toluene steam reforming.

Groundwater Remediation Using a Pyrolysis Oily Sludge Composite

The absorption capacity of oily sludge pyrolysis residue was utilized to prepare oxygen-releasing composites for groundwater remediation. The physical properties of the oily sludge pyrolysis residue were specific surface area of 13.936 m2/g and main pore size on the order of nanometers. The pyrolysis residue was nontoxic and would not cause secondary contamination of groundwater. The rate of mass loss of calcium peroxide and the oxygen release rate in water were analyzed. An oxygen-releasing composite containing 35% calcium peroxide, 15% oily sludge pyrolysis residue, 30% fluviatile sand, 10% calcium-based bentonite soil, and 10% deionized water was proposed. Addition of oily sludge to the composite plugged some of the oxygen-releasing surface and slowed the rate of oxygen release. Continuous precipitation of CaCO3 on the surface and in the pores of the composite also reduced the initial oxygen release rate and slowed the overall oxygen release rate.

Shape Effect of MnOx-Decorated CeO2 Catalyst in Diesel Soot Oxidation

Abstract A series of MnOx-decorated CeO2 (MnCeO) catalysts with different morphologies have been prepared by the shape-controlled synthesis of single-crystalline CeO2, such as nanorod, nanoparticle, and nanocube, by a hydrothermal method followed by the deposition of MnOx phase by a simple impregnation method. Their shape-dependent physicochemical properties were investigated by means of XRD, BET, UV–vis, HRTEM, XPS, TPR and oxygen storage/release properties measurements. The MnOx/CeO2 nanorod (MnCeO-NR) showed prominent carbon soot combustion activity at lower temperature under tight contact mode with a T50 temperature of 317 °C, which is attributed to larger surface area and higher oxygen release rate, as compared with particle and cubic catalysts. MnCeO-NR also exhibited higher catalytic activity (a shift of T50 by 127 °C) in NO-assisted soot combustion under a loose contact mode. Not only the higher surface area but also the superior NO conversion ability at low temperature as well as greater NO absorption contributes to the improved catalytic activities. The MnCeO-NR further displayed high stability and satisfactory recyclability without significant loss of catalytic activity. The use of cheaper combinations without noble metals makes the MnOx/CeO2 catalyst a promising candidate to satisfy future requirements in industry.

Use of Hopcalite-Derived Cu–Mn Mixed Oxide as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Process

An alternative to the chemical looping combustion process using solid fuels with CO2 capture is chemical looping with oxygen uncoupling (CLOU). The CLOU process requires an oxygen carrier with the capability to give gaseous O2 to burn solid fuels at the appropriate temperature, e.g., manganese oxide and copper oxide. In this work, treated commercial Carulite 300 was evaluated as oxygen carrier for CLOU. Carulite 300 is a hopcalite material composed of 29.2 wt % CuO and 67.4 wt % Mn2O3. The oxygen release rate and the fluidization behavior, with careful attention given to attrition rate and the behavior against agglomeration, were analyzed in a thermogravimetric analyzer and in batch fluidized bed reactors. Experiments in batch fluidized bed reactors were carried out at temperatures ranging from 800 to 930 °C with a medium volatile bituminous coal from South Africa and its char as fuels. The hopcalite-derived oxygen carrier showed high O2 release rate, no unburned products at low oxygen carrier–fuel mass r...

Differential Roles of Carotenes and Xanthophylls in Photosystem I Photoprotection.

Carotenes and their oxygenated derivatives, xanthophylls, are structural elements of the photosynthetic apparatus and contribute to increasing both the light-harvesting and photoprotective capacity of the photosystems. β-Carotene is present in both the core complexes and light-harvesting system (LHCI) of Photosystem (PS) I, while xanthophylls lutein and violaxanthin bind exclusively to its antenna moiety; another xanthophyll, zeaxanthin, which protects chloroplasts against photooxidative damage, binds to the LHCI complexes under conditions of excess light. We functionally dissected various components of the xanthophyll- and carotene-dependent photoprotection mechanism of PSI by analyzing two Arabidopsis mutants: szl1 plants, with a carotene content lower than that of the wild type, and npq1, with suppressed zeaxanthin formation. When exposed to excess light, the szl1 genotype displayed PSI photoinhibition stronger than that of wild-type plants, while removing zeaxanthin had no such effect. The PSI-LHCI complex purified from szl1 was more photosensitive than the corresponding wild-type and npq1 complexes, as is evident from its faster photobleaching and increased rate of singlet oxygen release, suggesting that β-carotene is crucial in controlling chlorophyll triplet formation. Accordingly, fluorescence-detected magnetic resonance analysis showed an increase in the amplitude of signals assigned to chlorophyll triplets in β-carotene-depleted complexes. When PSI was fractioned into its functional moieties, it was revealed that the boost in the rate of singlet oxygen release caused by β-carotene depletion was greater in LHCI than in the core complex. We conclude that PSI-LHCI complex-bound β-carotene elicits a protective response, consisting of a reduction in the yield of harmful triplet excited states, while accumulation of zeaxanthin plays a minor role in restoring phototolerance.

The strontium inorganic mutant of the water oxidizing center (CaMn4O5) of PSII improves WOC efficiency but slows electron flux through the terminal acceptors

Herein we extend prior studies of biosynthetic strontium replacement of calcium in PSII-WOC core particles to characterize whole cells. Previous studies of Thermosynechococcus elongatus found a lower rate of light-saturated O2 from isolated PSII-WOC(Sr) cores and 5–8× slower rate of oxygen release. We find similar properties in whole cells, and show it is due to a 20% larger Arrhenius activation barrier for O2 evolution. Cellular adaptation to the sluggish PSII-WOC(Sr) cycle occurs in which flux through the QAQB acceptor gate becomes limiting for turnover rate in vivo. Benzoquinone derivatives that bind to QB site remove this kinetic chokepoint yielding 31% greater O2 quantum yield (QY) of PSII-WOC(Sr) vs. PSII-WOC(Ca). QY and efficiency of the WOC(Sr) catalytic cycle are greatly improved at low light flux, due to fewer misses and backward transitions and 3-fold longer lifetime of the unstable S3 state, attributed to greater thermodynamic stabilization of the WOC(Sr) relative to the photoactive tyrosine YZ. More linear and less cyclic electron flow through PSII occurs per PSII-WOC(Sr). The organismal response to the more active PSII centers in Sr-grown cells at 45°C is to lower the number of active PSII-WOC per Chl, producing comparable oxygen and energy per cell. We conclude that redox and protonic energy fluxes created by PSII are primary determinants for optimal growth rate of T. elongatus. We further conclude that the (Sr-favored) intermediate-spin S=5/2 form of the S2 state is the active form in the catalytic cycle relative to the low-spin S=1/2 form.

Cyclic Oxygen Release Characteristics of Bifunctional Copper Oxide/Calcium Oxide Composites

AbstractIntegrated calcium–copper (Ca–Cu) looping is a novel carbon capture technology that uses copper oxide to transport oxygen and calcium oxide to capture CO2 in the same process. Investigations into the oxygen release behavior of the bifunctional CuO/CaO composite are critical to assess the potential for applying this technology to solid fuels such as coal. In this study, three different CuO/CaO composites having different relative percentages (CuO75CaO25, CuO50CaO50, and CuO25CaO75) were manufactured in a commercial granulator and then tested in a bubbling fluidized bed reactor to examine their oxygen release characteristics at temperatures in the 880–940 °C range. All the composites exhibited clear oxygen release properties during the testing, indicating that the solid fuel can be directly oxidized rather than being gasified first in the Ca–Cu looping process. At the same temperature, the oxygen release rate of CuO25CaO75 is the fastest and its final oxygen yield is the largest, followed by CuO75CuO25 and CuO50CaO50. XRD results reveal that Ca2CuO3 is formed in the used samples of CuO75CuO25 and CuO50CaO50, but not in the case of CuO25CaO75, which may explain the performance difference observed. Further examination of the attrition and agglomeration behavior shows that all the composites are stable and strong, and it appears that CuO25CaO75 is the most stable and strongest of the materials examined.

Oxidation of ammonia over a copper oxide-containing solid oxygen carrier with oxygen uncoupling capability

Measurements and modelling of the oxidation of ammonia over copper oxide (CuO) under conditions relevant to chemical-looping combustion with oxygen uncoupling show that CuO fully converts NH3 into NO or N2 under most of these conditions. Our experiments demonstrate that considerable amounts of NO are formed when the oxygen carrier is fully oxidised. Decreasing the degree of oxidation of the oxygen carrier affected the selectivity of the NH3 oxidation towards NO. Ageing of the oxygen carrier had a similar effect. Modelling suggests that these results reflect a change in the rate of oxygen release from the CuO particles.

Kinetics of oxygen uncoupling of a copper based oxygen carrier

Here, an oxygen carrier consisting of 60wt% CuO supported on a mixture of Al2O3 and CaO (23wt% and 17wt% respectively) was synthesised by wet-mixing powdered CuO, Al(OH)3 and Ca(OH)2, followed by calcination at 1000°C. Its suitability for chemical looping with oxygen uncoupling (CLOU) was investigated. After 25 repeated redox cycles in either a thermogravimetric analyser (TGA) or a laboratory-scale fluidised bed, (with 5vol% H2 in N2 as the fuel, and air as the oxidant) no significant change in either the oxygen uncoupling capacity or the overall oxygen availability of the carrier was found. In the TGA, it was found that the rate of oxygen release from the material was controlled by intrinsic chemical kinetics and external transfer of mass from the surface of the particles to the bulk gas. By modelling the various resistances, values of the rate constant for the decomposition were obtained. The activation energy of the reaction was found to be 59.7kJ/mol (with a standard error of 5.6kJ/mol) and the corresponding pre-exponential factor was 632m3/mol/s. The local rate of conversion within a particle was assumed to occur either (i) by homogeneous chemical reaction, or (ii) in uniform, non-porous grains, each reacting as a kinetically-controlled shrinking core. Upon cross validation against a batch fluidised bed experiment, the homogeneous reaction model was found to be more plausible. By accurately accounting for the various artefacts (e.g. mass transfer resistances) present in both TGA and fluidised bed experiments, it was possible to extract a consistent set of kinetic parameters which reproduced the rates of oxygen release in both experiments.

Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU)

Some binary and ternary combined manganese oxides of Mn with one or two additional metals or metalloids of Fe, Si, Ca and Mg were investigated as oxygen carriers for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). More specifically the following systems were investigated: (1) MnyMgOx, (2) CaMnO3–(Fe0.25Mn0.75)2O3, (3) CaMnO3–(Fe0.67Mn0.33)2O3, (4) CaMnO3–MnMgOx, (5) MnMgOx–(Fe0.25Mn0.75)2O3 and (6) Mn2SiOx–Fe2SiOx. The general trend was that the binary systems, where two metals are used in the formulation showed the most promising results in terms of oxygen uncoupling and reactivity. However, there are several ternary combinations which show a combination of high oxygen uncoupling, reactivity with methane and reasonable strength. A pseudo first-order effective rate constant was evaluated for the investigated particles. The measured rates are lower than for benchmark nickel oxide and calcium manganites, but higher than for ilmenite. The ternary System 6, Mn2SiOx–Fe2SiOx was investigated in more depth, including solid fuel experiments to determine the rate of oxygen release. At 850 and 900°C (Mn0.5Fe0.5)2SiOx had the highest average reactivity, with a maximum average yield of 91.5% at 850°C. On the other hand, at higher temperatures, the particles with the highest Mn content showed best behavior, i.e. (Mn0.67Fe0.33)2SiOx. Reactivity experiments with char in the FB reactor with this OC showed that the oxygen capacity for CLOU was high, 3.5wt% at 950°C, with a maximum release rate of 0.2gO2/kgOC,s. The low rate of uncoupling means that the experiments with gaseous fuel were likely dominated by the direct gas–solid reaction, and not CLOU. X-ray powder diffraction suggests that the main reaction path is via (MnxFe1−x)2O3 to (MnxFe1−x)3O4, although the reaction between Mn7SiO12 to MnSiO3 cannot be ruled out as a possible route of oxygen transfer. This was supported by thermodynamic calculations of this multi-component system.

Oxygen carrying microbubbles for enhanced sonodynamic therapy of hypoxic tumours

Microbubbles are proposed as a potentially novel method for oxygen delivery in vivo in initial studies. The lack of commercial microbubbles for oxygen delivery in preclinical research prompted us to fabricate an oxygen-loaded lipid microbubble. We aimed to extend the innovative strategy to modulate the tumor hypoxic microenvironment, using microbubbles intravenously as an oxygen carrier for the controllable tumor-specific delivery of oxygen by ultrasound (US). In our experiment, an oxygen-loaded lipid-coated microbubble (OLM) with mixed gas (O2/C3 F8, 5:1 v/v) was fabricated and exhibited a higher rate of oxygen release to a desaturated solution through burst by US than that in the absence of US. Although in in vivo studies, OLMs could be imaged and triggered by US to elevate the pO2 level in the breast VX2 tumor dramatically within a matter of minutes. The added presence of US-activated OLMs elicited a nearly six-fold increase in pO2 levels within 1 min compared with that of the pre-injection. Owing to the high oxygen payload, great acoustic stability and acoustic properties, OLMs may be proposed as an ideal radio-sensitizer. We conclude that oxygen release mediated by ultrasound-targeted microbubble destruction is feasible and shows potential in image-guided, site-specific cancer radiotherapy.

Isothermal Pressure-Swing Cycling of Strontium Doped Lanthanum Manganite Oxides for Fuel Production

Water splitting for fuel production via isothermal pressure-swing cycling has recently emerged as a means of converting solar heat to a storable medium [1]. For the generation of hydrogen, the process involves the high temperature reduction of a variable valence oxide under an inert gas of low oxygen content followed by oxidation by steam at the same high temperature. Due to thermolysis, the higher the temperature the greater the oxidizing power of the steam, providing a means of converting thermal energy to chemical energy. In comparison to a more conventional temperature-swing cycle, the isothermal, pressure-swing cycle offers the potential for greater efficiency because the need for solid state heat recovery is eliminated, although the demands on gas-phase heat recovery are increased. To date, isothermal, pressure-swing process has been demonstrated only using ceria. Here, we explore the behavior of perovskite-structured oxides as candidates for this cycle. In principle, fuel production capacity can be determined, a priori, from knowledge of the thermodynamic properties of a non-stoichiometric oxide. Accordingly, as a first step, the thermodynamics of various compositions of lanthanum strontium manganite oxides (LaxSr1-xMnO3) were modeled at high temperature from literature data [2]. The theoretical, equilibrium fuel production capacity at 1500°C is found, on the basis of this analysis, to exceed that of undoped ceria, by almost a factor of two (and more than a factor of three at 1400°C). Motivated by this result, samples of x = 0.1, 0.2, 0.3 and 0.4 were synthesized via solid state reaction and then experimentally evaluated for fuel productivity using in an in-house constructed thermochemical reactor. Cycling between Ar (with 10 ppm oxygen) and 20% steam (balance Ar) at 1500°C shows that indeed the series of materials offer higher fuel production capacity under conditions of long-cycle times. In addition, oxygen release rates are higher for the perovskites than they are for ceria, indicating that more fuel is produced for a given cycle with finite periods.

Bioremediation Modeling of an Aquifer Contaminated by Benzene Using the Slow-Release Oxygen Source Technique

Groundwater contamination caused by petroleum products has become a common problem. These hazardous chemicals themselves soak down into groundwater through the soil or rock and cause significant health risk. Benzene, one species of chemicals, gives rise to specific concerns due to its relatively high water solubility and toxicity. For the removal of benzene in aquifer, natural biodegradation has indicated its limited ability because of the lack of dissolved oxygen (DO) in groundwater. A new method, namely the slow-release oxygen source (SOS) technique, could increase concentration of dissolved oxygen in groundwater and accelerate biodegradation processes. Therefore, the paper first built a transport model including benzene, DO and microbial species. Relevant program codes were developed on the basis of MODFLOW/MT3DMS. Then, a two-dimensional synthetic aquifer with a point source of benzene was simulated by the modified model to analyze the treatment efficiency of SOS. There were seven schemes designed by using different locations of well and oxygen release rates. Their treatment efficiencies were analyzed. The results showed that the modified model can be used to simulate benzene transport under SOS technique where Monod kinetic reactions occur. It was more efficient when placing release oxygen well was close to contamination sources of groundwater. For the same location of well, higher release rate of oxygen would enhance the effect of bioremediation. Enough dissolved oxygen maybe accelerates the growth of microbial species, and more benzene could be consumed by increasing microbial mass.

Transient heat and mass transfer analysis in a porous ceria structure of a novel solar redox reactor

Thermal transport processes are numerically analyzed for a porous ceria structure undergoing reduction in a novel redox reactor for solar thermochemical fuel production. The cylindrical reactor cavity is formed by an array of annular reactive elements comprising the porous ceria monolith integrated with gas inlet and outlet channels. Two configurations are considered, with the reactor cavity consisting of 10 and 20 reactive elements, respectively. Temperature dependent boundary heat fluxes are obtained on the irradiated cavity wall by solving for the surface radiative exchange using the net radiation method coupled to the heat and mass transfer model of the reactive element. Predicted oxygen production rates are in the range 40–60 μmol s−1 for the geometries considered. After an initial rise, the average temperature of the reactive element levels off at 1660 and 1680 K for the two geometries, respectively. For the chosen reduction reaction rate model, oxygen release continues after the temperature has leveled off which indicates that the oxygen release reaction is limited by chemical kinetics and/or mass transfer rather than by the heating rate. For a fixed total mass of ceria, the peak oxygen release rate is doubled for the cavity with 20 reactive elements due to lower local oxygen partial pressure.

Sulfur Tolerance and Rate of Oxygen Release of Combined Mn–Si Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)

Sulfur tolerance and rate of oxygen release of combined Mn–Si oxygen carriers for chemical-looping with oxygen uncoupling (CLOU) is investigated. The oxygen carriers were produced by spray-drying and calcined at 1150 °C. The resistance toward sulfur and the rates of oxygen release were evaluated in a laboratory-scale fluidized-bed reactor. It was found that the combined Mn–Si oxygen carrier is tolerant to SO2, at least up to a partial pressure of 5000 vppm. The rates of oxygen release were determined in the temperature range of 975 to 1100 °C using devolatilized wood char as fuel while fluidizing with N2, to maintain a low oxygen partial pressure surrounding the particles. The Arrhenius parameters ko and Eapp for the release of oxygen were estimated for the investigated materials assuming a zero-order reaction with respect to oxygen. The rates of oxygen release were relatively high, particularly at above 1050 °C. From the obtained reaction rates, the solids inventory required for combustion of coal was determined to be as low as 40 kg/MWth in the fuel reactor at 1100 °C. The results indicated that combined Mn–Si oxygen carriers could be interesting materials for the CLOU process by virtue of their resistance to sulfur deactivation and high rate of oxygen release.