Oxygen Reactivity Research Articles

Patterns of Formation of Binary Cobalt–Magnesium Oxide Combustion Catalysts of Various Composition

In order to establish the formation patterns of the Co–Mg oxide system, samples with different Co:Mg ratios and heat treatment temperatures were synthesized and studied. A study of the samples confirmed the phase transition of MgxCo2–xO4 spinels into the corresponding solid solutions at 800–900 °C. The similarity of the formation patterns for different compositions is shown. The rocksalt oxide in low-temperature samples is an anion-modified paracrystalline phase that forms a “true” solid solution only upon spinel decomposition. The TPR profiles of the decomposed Co3O4 spinel show surface Co3O4 peaks and a wide peak corresponding to the well-crystallized CoO, while partial Co3O4 TPR up to 380 °C results in dispersed and amorphous CoO. The high-temperature non-stoichiometric samples are poorly reduced, indicating their low oxygen reactivity. Spinel reoxidation after heat treatment to 1100 °C by calcination at 750 °C showed complete regeneration for MgCo2O4–Co3O4 samples and its absence in case of an excess of MgO relative to stoichiometry.

Synthetic Copper-(Di)oxygen Complex Generation and Reactivity Relevant to Copper Protein O2-Processing.

Synthetic copper-dioxygen complex design, generation and characterization, play a crucial role in elucidating the structure/function of copper-based metalloenzymes, including dopamine β-monooxygenase, lytic polysaccharide monooxygenases, particulate methane monooxygenase, tyrosinase, hemocyanin, and catechol oxidase. Designing suitable ligands to closely mimic the variable active sites found in these enzymes poses a challenging task for synthetic bioinorganic chemists. In this review, we have highlighted a few representative ligand systems capable of stabilizing various copper-dioxygen species such as CuII-(O2 •-)(superoxide), Cu2 II-(μ-η 1:η 1-O2 2-) (trans/cis-peroxide), Cu2 II-(μ-η 2:η 2-O2 2-)(side-on peroxide) and Cun II--OOH (hydroperoxide) species. Here, we discuss the ligand type utilized, syntheses, and spectroscopic characterization of these species. We also delineate reactivity patterns, particularly electrophilic arene hydroxylation by a side-on peroxo species which occurs via a "NIH shift" mechanism and thermodynamic-kinetic relationships among Cu2-(O2 •-)/O2 2-/-OOH moieties.

Geochemical impact of biomethane and natural gas blend injection in deep aquifer storage

Biomethane is one of the main renewable gases available today to offset fossil gas and decarbonize the energy system. The EU is seeking to rapidly replace part of the natural gas usually stored in deep saline aquifers by biomethane which contains up to 10000 ppm of O2. This study presents for the first-time assessment of deep aquifers’ resilience to biomethane and natural gas blend injection into two sandstone reservoirs with different mineral paragenesis from the Paris Basin (France). Multiphase reactive transport modeling allowed to evaluate changes in gas and water quality, mineralogy and moreover, to identify major resilience properties of storage facilities necessary to buffer the oxygen reactivity and induced acidification coming from gas–water–rock interactions. In the presence of pyrite, the injected oxygen is consumed during pyrite oxidation and contributes to the acidification of the formation water close to the injection point. However, the injection of 1% mole fraction of CO2(g) contained in the gas blend is found to be the main acidification factor. The analysis of reservoir resilience showed three protection levels of pH buffering capacity, which can effectively mitigate an increase in oxygen content up to 1000 ppm: (i) calcite dissolution, (ii) plagioclase and clay dissolution and (iii) clay sorption capacity. Models predict that the gas blend injection could induce minimal but long-term change in the mineralogy without significantly impacting the global porosity. Overall, both sandstones can preserve the quality of the gas plume despite partial CO2(g) exsolution induced by the geochemical perturbation of the formations. The developed models will be used as a basis for assessment of renewable natural gas storage facilities in the long-term.

Electronic and Steric Effects on Oxygen Reactivities of NiFeSe Complexes Related to O2-Damaged [NiFeSe]-Hydrogenases’ Active Site

Hydrogen has the potential to serve as a new energy resource, reducing greenhouse gas emissions that contribute to climate change. Natural hydrogenases exhibit impressive catalytic abilities for hydrogen production, but they often lack oxygen tolerance. Oxygen-tolerant hydrogenases can work under oxygen by reacting with oxygen to form inactive states, which can be reactivated to catalytic states by oxygen atom removal. Herein, we synthesized three NiFeSe complexes: (NiSe(CH3)FeCp, NiSe(CH3)FeCp* and NiSe(PhNMe2)FeCp) with features of active sites of [NiFeSe]-H2ases, which are the oxygen-tolerant hydrogenases, and we investigated the influence of electronic and steric factors on the oxygen reaction of these “biomimetic” complexes. In our research, we found that they react with oxygen, forming 1-oxygen species, which is related to the O2-damaged [NiFeSe] active site. Through a comparative analysis of oxygen reactions, we have discovered that electronic factors and steric hindrance on Se play a significant role in determining the oxygen reactivity of NiFe complexes related to hydrogenases’ active sites.

#1553 Effects of proteinuria on muscle oxygenation and microvascular reactivity in patients with pre-dialysis CKD: a post-hoc analysis

Abstract Background and Aims Vascular dysfunction is a hallmark of CKD. Previous studies showed an impaired microvascular reactivity in the skeletal muscles, which deteriorates in advanced CKD stages. This analysis aims to examine the impact of proteinuria on skeletal muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with pre-dialysis CKD. Method 66 patients with CKD stage 2-4 were included in this post-hoc analysis; 24-h urine samples were used for evaluation of proteinuria. Continuous measurement of muscle oxygenation [tissue saturation index (TSI%)] via near-infrared-spectroscopy at rest, during occlusion-reperfusion and during a 3-min handgrip exercise (at 35% of maximal-voluntary-contraction). Results The study groups were similar in terms of age (proteinuric vs nonproteinuric: 68.4 ± 10.6 vs 67.2 ± 10.8; p = 0.676), eGFR (41.3 ± 18.9 vs 46.3 ± 14.8; p = 0.248) and BMI (28.4 ± 4.9 vs 28.1 ± 4.8; p = 0.803). Resting muscle oxygenation did not differ between study groups (proteinuric vs nonproteinuric: 63.35 ± 4.09 vs 62.34 ± 3.21; p = 0.280). During occlusion, proteinuric CKD patients had marginally lower TSI occlusion magnitude (25.77 ± 7.87 vs 29.95 ± 10.34; p = 0.074) but no difference in occlusion slope (−0.09 ± .03 vs -.10 ± .04; p = 0.134). During reperfusion, the TSI reperfusion slopes were significantly lower in proteinuric CKD (slope to max 1.03 ± .45 vs 1.39 ± 0.69; p = 0.035 and 10-sec slope: 1.34 ± .63 vs 1.92 ± .75; p = 0.002); hyperemic response was numerically lower in proteinuric CKD (7.13 ± 4.27 vs 8.89 ± 4.68; p = 0.131). Finally, during exercise no differences were detected in the average muscle oxygenation between-group (10.76 ± 6.05 vs 10.65 ± 5.39; p = 0.943). Conclusion Although no differences in resting muscle oxygenation were detected, CKD patients with proteinuria showed more impaired skeletal muscle oxidative capacity (as suggested by lower TSI magnidute during occlusion), and miscrovascular reactivity during reperfusion.

Modulating the Mn–O strength of OMS-2 by alkali metal doping for the catalytic oxidation of N, N-dimethylformamide

Promoting catalytic activity by engineering oxygen mobility and reactivity is an intriguing approach to heterogeneous catalysis. Through the cation-exchange method, alkali metals were introduced into the OMS-2 catalyst, resulting in a weakening of internal Mn–O bonds and an increase in surface oxygen vacancies. Alkali metal doping significantly enhanced the catalytic activity of OMS-2 in the catalytic oxidation of N, N-dimethylformamide (DMF). Specifically, Rb-OMS-2, obtained by doping of Rb into OMS-2, displayed the highest oxygen vacancy, oxygen mobility and reactive lattice oxygen. The Rb-OMS-2 catalyst displayed better catalytic performance with 100 % CO2 yield, lowest N2O concentration and excellent water resistance, and stabilized at 220 °C for more than 120 h. In situ DRIFTS revealed that DMF molecules reacted with three kinds of oxygen species, then breakage of the C–N bond occurred, finally the remaining C-containing groups were subsequently oxidized to CO2, and intermediates of –NH2 and –NO+ reacted to form N2.

An active site mutation induces oxygen reactivity in D-arginine dehydrogenase: A case of superoxide diverting protons

Enzymes are potent catalysts that increase biochemical reaction rates by several orders of magnitude. Flavoproteins are a class of enzymes whose classification relies on their ability to react with molecular oxygen (O2) during catalysis using ionizable active site residues. Pseudomonas aeruginosa D-arginine dehydrogenase (PaDADH) is a flavoprotein that oxidizes D-arginine for P.aeruginosa survival and biofilm formation. The crystal structure of PaDADH reveals the interaction of the glutamate 246 (E246) side chain with the substrate and at least three other active site residues, establishing a hydrogen bond network in the active site. Additionally, E246 likely ionizes to facilitate substrate binding during PaDADH catalysis. This study aimed to investigate how replacing the E246 residue with leucine affects PaDADH catalysis and its ability to react with O2 using steady-state kinetics coupled with pH profile studies. The data reveal a gain of O2 reactivity in the E246L variant, resulting in a reduced flavin semiquinone species and superoxide (O2•-) during substrate oxidation. The O2•- reacts with active site protons, resulting in an observed nonstoichiometric slope of 1.5 in the enzyme's log (kcat/Km) pH profile with D-arginine. Adding superoxide dismutase results in an observed correction of the slope to 1.0. This study demonstrates how O2•- can alter the slopes of limbs in the pH profiles of flavin-dependent enzymes and serves as a model for correcting nonstoichiometric slopes in elucidating reaction mechanisms of flavoproteins.

Effect of nanostructure and BET surface area on the oxygen reactivity of soot filter cakes

The oxygen reactivity of propane flame soot in a filter cake was systematically investigated, considering the morphological properties of the particles. A scanning mobility particle sizer (SMPS), high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy were used to determine the initial aggregate size, the primary particle size, and the nanostructure of the soot particles. The samples were analyzed using an experimental setup, which enables oxidation and in-situ measurement of the BET surface, revealing its development as the reaction progresses. Particles with five different mobility diameters were generated using a combustion aerosol standard (CAST) soot generator. While the nanostructure of the particles was similar at four operating points, the particles with the smallest mobility diameter differed as they were more amorphous, which was consistently seen in HRTEM images and Raman spectra. The results showed that for the particles with similar nanostructure, the mobility diameter, the size of the primary particles and the initial surface area correlate. These particles have similar oxygen reactivity. The amorphous particles instead, showed a significantly higher reactivity, despite having the lowest specific surface area. The nanostructure appears to be decisive for the reactivity. Further the results clearly showed that surface area development affects the soot conversion profiles. Surface-normalized reaction kinetics for soot at each operation point were formulated.

Tailoring indium oxide film characteristics through oxygen reactants in atomic layer deposition with highly reactive liquid precursor

Indium oxide (InOx) films were deposited via atomic layer deposition (ALD) using a novel liquid indium precursor, dimethyl[N1-(tert-butyl)–N2,N2-dimethylethane-1,2-diamine]indium (DMITN). In this process, the reactant (H2O, O3, or O2 plasma) and substrate temperature (100–250 ℃) were varied. The DMITN precursor showed excellent reactivity with all three reactants. The growth characteristics (ALD window, growth per cycle, and step coverage) and film properties (impurities, stoichiometry, oxygen bonding state, crystallinity, film density, and electrical properties) differed based on the ALD process employed, ascribed to the distinct thermal energies and inherent reactivities of the chosen oxidants. As the oxidation energy of the reactants increased (H2O < O3 < O2 plasma), the growth per cycle (GPC) and the oxygen–indium bond ratio of InOx increased. Crystallinity analysis also revealed significant differences depending on the reactants, where the Hall mobility was predominantly influenced by the crystal alignment. The step coverage at an aspect ratio of 40:1 was markedly superior with the use of H2O and O3 reactants (approximately 95 %) compared to that with O2 plasma (approximately 74 %). These findings highlight the capability of controlling the growth and properties of InOx films by judiciously selecting the reactant, emphasizing the versatility of the DMITN precursor in ALD processes.

Self-assembled La0.7Sr0.3Fe0.9Ni0.1O3-δ-Ce0.8Sm0.2O2-δ composite cathode with a three-dimensional ordered macroporous structure for protonic ceramic fuel cells

Self-assembled La0.7Sr0.3Fe0.9Ni0.1O3-δ-Ce0.8Sm0.2O1.9-δ (LSFN-SDC) composite cathode with a three-dimensionally ordered macroporous (3DOM) structure is synthesized using poly(methyl methacrylate) as the template for protonic ceramic fuel cells. The LSFN and SDC phases both distribute uniformly in the cathode. The SDC phase reduces the thickness of the walls of the 3DOM structure and thus hinders the bulk conduction of electrons. SDC also decreases the specific surface area and the surface oxygen reactivity of the cathode, leading to the suppression of the adsorption and dissociation of O2. However, the SDC phase provides the conduction pathway for oxygen ions and enlarges three phase boundary consequently, which facilitates the charge transfer steps. The thickness of the walls and the specific surface area of the composite cathode are both increased with the rise of the concentration of the nitrate precursor solution, resulting in the acceleration of the cathode process. Nevertheless, an excessive precursor concentration leads to the destroy of the 3DOM structure. The 3DOM composite cathode exhibits the lowest Rp of 0.039 Ω cm2, and a single cell with that cathode shows maximum power density of 1484 mW cm−2 at 700 °C. The cell exhibits a short-term stability of 120 h at 700 °C without noticeable degradation.

EFFECTS OF PROTEINURIA ON MUSCLE OXYGENATION AND MICROVASCULAR REACTIVITY IN PATIENTS WITH PRE-DIALYSIS CKD: A POST-HOC ANALYSIS

Objective: Vascular dysfunction is a hallmark of CKD. Previous studies showed an impaired microvascular reactivity in the skeletal muscles, which deteriorates in advanced CKD stages. This analysis aims to examine the impact of proteinuria on skeletal muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with pre-dialysis CKD. Design and method: 66 patients with CKD stage 2-4 were included in this post-hoc analysis; 24-h urine samples were used for evaluation of proteinuria. Continuous measurement of muscle oxygenation [tissue saturation index (TSI%)] via near-infrared-spectroscopy at rest, during occlusion-reperfusion and during a 3-min handgrip exercise (at 35% of maximal-voluntary-contraction). Results: The study groups were similar in terms of age (proteinuric vs nonproteinuric: 68.4±10.6 vs 67.2±10.8; p=0.676), eGFR (41.3±18.9 vs 46.3±14.8; p=0.248) and BMI (28.4±4.9 vs 28.1±4.8; p=0.803). Resting muscle oxygenation did not differ between study groups (proteinuric vs nonproteinuric: 63,35±4,09 vs 62,34±3,21; p=0.280). During occlusion, proteinuric CKD patients had marginally lower TSI occlusion magnitude (25,77±7,87 vs 29,95±10,34; p=0.074) but no difference in occlusion slope (-0,09±.,03 vs -,10±.,04; p=0.134). During reperfusion, the TSI reperfusion slopes were significantly lower in proteinuric CKD (slope to max 1,03±.,45 vs 1,39±.0,69; p=0.035 and 10-sec slope: 1,34±.,63 vs 1,92±.,75; p=0.002); hyperemic response was numerically lower in proteinuric CKD (7,13±.4,27 vs 8,89±.4,68; p=0.131). Finally, during exercise no differences were detected in the average muscle oxygenation between-group (10,76±6,05 vs 10,65±5,39; p=0.943). Conclusions: Although no differences in resting muscle oxygenation were detected, CKD patients with proteinuria showed more impaired skeletal muscle oxidative capacity (as suggested by lower TSI magnidute during occlusion), and miscrovascular reactivity during reperfusion.

The regulation mechanism of transition metal doping on Hg0 adsorption and oxidation on Ce/TiO2(001) surface: A DFT study

The mercury oxidation performance of Ce/TiO2 catalyst can be further enhanced by transition metal modifications. This study employed density functional theory (DFT) calculations to investigate the adsorption and oxidation mechanisms of Hg0 on Ce/TiO2(001) and its transition metal modified surfaces. According to the calculation results, Ru-, Mo-, Nb-, and Mn-doping increased the affinity of the Ce/TiO2(001) surface towards Hg0 and HCl, thereby facilitating the efficient capture and oxidation of Hg0. The increased adsorption energy (Eads) of the intermediate HgCl on the modified surfaces could promote its conversion to the final product HgCl2. The modification of transition metals impeded the desorption of the final products HgCl2 and HgO, but it did not serve as the rate-determining step. The oxidation of Hg0 by lattice oxygen and HCl followed the Mars-Maessen and Langmuir-Hinshelwood mechanisms, respectively. HCl exhibited higher mercury oxidation ability than lattice oxygen. The reactivity of lattice oxygen could be further improved by doping transition metals, their promotion order was Ru > Nb > Mo > Mn. In a HCl atmosphere, Mn modification could significantly reduce the energy barrier for HCl activation and HgCl2 formation, providing the optimal enhancement for the mercury oxidation ability of Ce/TiO2 catalyst. The screening method of transition metal modified components based on surface adsorption reaction and oxidation energy barrier was proposed in this study, which provided theoretical guidance for the development of CeTi based catalysts with high mercury oxidation activity.

Effects of Mo doping on the structure, adsorption performance, and photocatalytic activity of LaFeO3 nanoparticles: Experimental and DFT studies

In this study, a series of Mo-doped LaFeO3 composite photocatalyst nanoparticles (x-LFMO, x = 0.33, 0.5, 0.67) were synthesized by ultrasonic-assisted sol–gel method under controlled Mo doping. X-ray diffraction (XRD) analyses indicate that Mo substitutes one-third of the Fe atoms in the B site of the LaFeO3 to form orthogonal perovskite structures LaFe0.67Mo0.33O3, which is the only pure phase crystal formed at stoichiometric Fe to Mo ratios of 2:1, 1:1, and 1:2, respectively. SEM and N2 adsorption/desorption revealed significantly smaller particle sizes (30–50 nm) and the formation of rich channels after Mo doping, thus enriching the specific surface area and pore size dispersion. DRS confirmed that the Mo-doped LFO composites exhibit significantly enhanced absorption in the visible region. This can be further explained by DFT theoretical calculations of energy band structures and density of states, which demonstrate that the effective mass of the electrons in LaFe0.67Mo0.33O3 is reduced and the off-domain properties of the electrons are enhanced, facilitating the excitation and transport of the photogenerated electrons. Kinetic studies showed that Mo-doped composite nanoparticles exhibit excellent adsorption capacity for quinoline, indole, and pyridine, and the pure phase LaFe0.67Mo0.33O3 and 0.5-LFMO performed well for them with removal efficiencies (>98 %) under visible light irradiation. Based on experimental observations and theoretical insights, it is suggested that the higher quantum yield and photocatalytic reactivity of x-LFMO composites are attributed to the bulk oxygen mobility and surface oxygen reactivity promoted by the octahedral distortion of BO6 in LaFe0.67Mo0.33O3 and the heterogeneous structure formed at the interface of the two phases.

Enhancing AsH3 Detoxification via Electron-Deficient [NiIII-OH (μ-O)] in a Nickel-Modified NaY Zeolite: A Pathway toward As0 Products.

The transformation of toxic arsine (AsH3) gas into valuable elemental arsenic (As0) from industrial exhaust gases is important for achieving sustainable development goals. Although advanced arsenic removal catalysts can improve the removal efficiency of AsH3, toxic arsenic oxides generated during this process have not received adequate attention. In light of this, a novel approach for obtaining stable As0 products was proposed by performing controlled moderate oxidation. We designed a tailored Ni-based catalyst through an acid etching approach to alter interactions between Ni and NaY. As a result, the 1Ni/NaY-H catalyst yielded an unprecedented proportion of As0 as the major product (65%), which is superior to those of other reported catalysts that only produced arsenic oxides. Density functional theory calculations clarified that Ni species changed the electronic structure of oxygen atoms, and the formed [NiIII-OH (μ-O)] active centers facilitated the adsorption of AsH2*, AsH*, and As* reaction intermediates for As-H bond cleavage, thereby decreasing the direct reactivity of oxygen with the arsenic intermediates. This work presents pioneering insights into inhibiting excessive oxidation during AsH3 removal, demonstrating potential environmental applications for recovery of As0 from toxic AsH3.

Sensing and Imaging Molecular Oxygen in Mammals with Spin Lattice Relaxation Electron Paramagnetic Resonance.

Molecular oxygen and its thermodynamic transformation drive nearly all life processes. Quantitative measurement and imaging of oxygen in living systems is of fundamental importance for the study of life processes and their aberrations-disease- many of which are affected by hypoxia, or low levels of oxygen. Cancer is among the disease processes profoundly affected by hypoxia. Electron paramagnetic resonance has been shown to provide remarkably accurate images of normal and cancerous tissue. In this review, we emphasize the reactivity of molecular oxygen particularly highlighting the metabolic processes of living systems to store free energy in the reactants. The history of hypoxic resistance of living systems to cytotoxic therapy, particularly radiation therapy is also reviewed. The measurement and imaging of molecular oxygen with pulse spin lattice relaxation (SLR) electron paramagnetic resonance (EPR) is reviewed briefly. This emphasizes the advantages of the spin lattice relaxation based measurement paradigm to reduce the sensitivity of the measurement to the presence of the oxygen sensing probe itself. The involvement of a novel small mammal external beam radiation delivery system is described. This enables an experimental paradigm based on control by radiation of the last resistant clonogen. This is much more specific for tumor cure than growth delay assays which primarily reflects control of tumor cells most sensitive to therapy.

Magnetic manipulation of the reactivity of singlet oxygen: from test tubes to living cells.

Although magnetism undoubtedly influences life on Earth, the science behind biological magnetic sensing is largely a mystery, and it has proved challenging, especially in the life sciences, to harness the interactions of magnetic fields (MFs) with matter to achieve specific ends. Using the well-established radical pair (RP) mechanism, we here demonstrate a bottom-up strategy for the exploitation of MF effects in living cells by translating knowledge from studies of RP reactions performed in vitro. We found an unprecedented MF dependence of the reactivity of singlet oxygen (1O2) towards electron-rich substrates (S) such as anthracene, lipids and iodide, in which [S ˙+ O2 ˙-] RPs are formed as a basis for MFs influencing molecular redox events in biological systems. The close similarity of the observed MF effects on the biologically relevant process of lipid peroxidation in solution, in membrane mimics and in living cells, shows that MFs can reliably be used to manipulate 1O2-induced cytotoxicity and cell-apoptosis-related protein expression. These findings led to a 'proof-of-concept' study on MF-assisted photodynamic therapy in vivo, highlighting the potential of MFs as a non-invasive tool for controlling cellular events.

Superfast hydrous-molten salt erosion to fabricate large-size self-supported electrodes for industrial-level current OER

Durable, active, and cheap oxygen evolution reaction (OER) electrocatalyst to replace the noble metal-based ones is appealing but challenging in energy storage fields. Here, we devise a one-pot low-temperature hydrous molten salt erosion strategy to vertically root the thin and dense bimetal hydroxide (NiFeOxHy) nanosheet on commercial nickel foam in 1 min. The defect-rich nanosheets are interdigitated together to yield a highly porous array, which offers affluent exposed electroactive centers, decreased charge/mass transfer, and augmented mechanical stability, while a strong Ni-Fe synergy elicits the signal redox reactivity of both metal and nonmetal lattice oxygen. Due to such effects, the typical NiFeOxHy electrode accesses a catalytic current of 10 mA cm−2 at a low overpotential 216 mV for freshwater electrolyte and 232 mV for saline one both with a small Tafel slope of 53 mV dec−1, while stably working for 1000 h at 0.1 A cm−2 in freshwater electrolyte and over 550 h at 1 A cm−2 in saline one. This evidences efficient and stable large-current–density OER performance, particularly a strong Cl− anti-erosion. The large-scale NiFeOxHy electrode materials (81 cm2) with a commensurate performance are fabricated on nickel foam, heralding the enormous prospect for practical usage. This exceedingly procedure-, energy- and time-saving erosion tactic can be generalized to common metal foam substrates and hydrous metal molten salts, accenting a momentous stepping stone for integral construction of self-supported and large-size electrodes towards commercially-met OER application and beyond.

Crystalline phase transformation of Sr-Fe based oxygen carriers modulate the cyclic performance for syngas and CO coproduction in chemical looping ethanol reforming coupled with CO2 splitting

The chemical looping reforming coupled with CO2 splitting (CLR-CS) offers a promising solution for syngas production and simultaneous decomposition of CO2. In this study, the Sr-Fe based oxygen carriers (OCs) were evaluated in CLR-CS using ethanol as fuel. The presence of Sr significantly improved the oxidation performance of iron oxides. The Sr element in fresh Sr-Fe based OCs mainly formed two crystal phases, including SrFe12O19 and Sr4Fe6O13. Increasing the amount of Sr element made it easier to form Sr4Fe6O13 crystal phase. The Sr4Fe6O13 was favorable for syngas production, due to the higher surface oxygen vacancy formation energy with a range of 3.13–3.37 eV. However, the lower oxygen transfer capacity (OTC) of Sr4Fe6O13 resulted in a lower CO yield in the of stage of CO2 decomposition. Compared with Sr4Fe6O13, SrFe12O19 exhibited the higher OTC and the higher reactivity of lattice oxygen, which was preferable to produce more CO2 in the stage of ethanol reforming in fuel reactor. During the cycle tests, the crystalline phase of SrFe12O19 didn’t regenerate under the CO2 atmosphere but transformed into Sr4Fe6O13. It was attributed to the lower energy barrier of CO2 oxidation on the oxygen defect surface of Sr4Fe6O13. The phase transformation of SrFe12O19 accompanied the formation of Fe3O4. The excessive Fe3O4 had poor stability and inactivated easily due to sintering and agglomeration in Sr1Fe4 and Sr1Fe6 samples. The Sr1Fe2, namely the molar ratio of SrO to Fe2O3 of 1:2, exhibited the better performance for syngas (0.291 Nm3/kg OC) and CO (0.141 Nm3/kg OC) coproduction at 800 °C. Additionally, the Sr1Fe2 presented an excellent cyclic stability in 30 cycles due to the suitable proportion of Sr4Fe6O13 and iron oxides formed, which maintained a high syngas yield and avoided sintering of iron oxides. Overall, the Sr1Fe2 is a promising OC candidate in CLR-CS process.

Synthetic dioxygenase reactivity by pairing electrochemical oxygen reduction and water oxidation.

The reactivity of molecular oxygen is crucial to clean energy technologies and green chemical synthesis, but kinetic barriers complicate both applications. In synthesis, dioxygen should be able to undergo oxygen atom transfer to two organic molecules with perfect atom economy, but such reactivity is rare. Monooxygenase enzymes commonly reductively activate dioxygen by sacrificing one of the oxygen atoms to generate a more reactive oxidant. Here, we used a manganese-tetraphenylporphyrin catalyst to pair electrochemical oxygen reduction and water oxidation, generating a reactive manganese-oxo at both electrodes. This process supports dioxygen atom transfer to two thioether substrate molecules, generating two equivalents of sulfoxide with a single equivalent of dioxygen. This net dioxygenase reactivity consumes no electrons but uses electrochemical energy to overcome kinetic barriers.

CuxMg1-xFe2O4-type spinels as potential oxygen carriers for waste wooden biomass combustion

Waste wood biomass is considered a renewable energy source. Combining biomass combustion with emerging clean combustion technologies such as chemical looping combustion (CLC) can yield effective and affordable carbon capture and, consequently, lead to negative net emissions of greenhouse gases. Oxygen carrier (OC) is a crucial material in CLC technology that must exhibit certain properties, such as high durability, good chemical stability during numerous red-ox cycles and, important for the combustion of solid fuels, the capability of spontaneously releasing oxygen in a process referred to as chemical looping with oxygen uncoupling (CLOU). In this work, a series of nine CuxMg1-xFe2O4 spinel-based materials were synthetized and evaluated for the first time as potential OCs for a waste biomass combustion. Their properties, such as oxygen transport capacity and reactivity with biomass (wood chips) as a fuel, were evaluated in a function of temperature (900–1000 °C). Tested oxygen carriers were characterized with an excellent oxygen transport capacity in CLOU process (up to 2.78 wt%) and good reaction rates with the fuel (up to 1.19 wt. %/min), and regeneration rates (up to 3.8 wt. %/min). High conversion of the waste biomass was also achieved (98.9 %). Moreover, new findings revealed a strong positive effect of magnesium addition on mechanical strength (crushing strength > 4 N for samples with Mg content above 0.5).