Oxygen Storage Research Articles

Halite-structured (MgCoNiMnFe)Ox high entropy oxide (HEO) for chemical looping dry reforming of methane

The configurational disorder of high entropy oxides (HEOs) promotes the reversible exsolution–redissolution of constituent metal species. This unique feature could be exploited to facilitate cyclic lattice oxygen storage and exchange. Herein, we report an in situ generated, halite-structured (MgCoNiMnFe)Ox HEO, which simultaneously functions as a redox catalyst and an oxygen carrier for dry reforming of methane in a chemical looping process (CL–DRM). Accordingly, the (MgCoNiMnFe)Ox/ZrO2 HEO catalyst exhibits outstanding DRM activity, syngas selectivity and cyclic stability compared to medium-entropy oxides and bimetallic oxides over 100 CL–DRM cycles at 800 °C. XRD analysis verified the entropy-mediated preservation of the alloy/HEO/ZrO2 catalytic structure over CL–DRM cycles. XAFS studies revealed the reversible and cyclic evolution–dissolution of Ni, Fe, Co over redox cycles. The exsolved NiFeCo nanoalloy exhibited high efficiency in activating CH4. This study has demonstrated the potential applications of HEO-based catalysts in efficient chemical looping processes.

Surface oxygen vacancy vs oxygen storage capacity in cubic ceria based nanocatalysts for low temperature catalytic combustion of fuels

A series of praseodymium (Pr) doped cubic ceria nanoparticles (CeO2 NPs) with different ratio of cerium (Ce) and ‘Pr’ was synthesized by hydrothermal method. Manganese (‘Mn’) doped cubic CeO2 NPs with 10:90 ratio of Mn:Ce and undoped cubic CeO2 NPs have also been synthesized. The crystalline structure of the synthesized nanomaterials has been studied by powder X-Ray diffraction (XRD) and Rietveld analysis. In the Raman spectrum, the intensity of F2g signal at 450–460 cm−1 decreased while the intensity of extrinsic vacancy at 570–580 cm−1 increased by doping with ‘Pr’ or ‘Mn’ in cubic CeO2 nanocrystals. X-ray photoelectron spectroscopy (XPS) results showed that surface oxygen vacancy of cubic CeO2 NPs increased by doping with 25 % of ‘Pr’. The ‘Pr’ doped CeO2 NPs (Pr:Ce = 25:75) exhibited higher surface adsorption dynamic oxygen storage capacity (OSCDyn), while the ‘Mn’ doped cubic CeO2 NPs (Mn:Ce = 10:90) showed increased bulk lattice OSCDyn. The ‘Pr’ doped cubic CeO2 NPs (Pr:Ce = 25:75) exhibited better low temperature catalytic combustion activity, and their nanodispersion in mineral turpentine oil (MTO) added liquefied petroleum gas (LPG) exhibited better fuel efficiency with a flame temperature of 912 °C.

Simultaneous catalytic oxidation of Hg0 and NO over CoxCuy metal oxides catalyst

In this work, Co3O4, CoxCuy and CuO metal oxides catalysts were synthesized by coprecipitation method and tested in catalytic oxidation of Hg0 and NO. The Co3Cu1 catalyst exhibited nearly 100% Hg0 oxidation efficiency at 100–400 ℃ and 84% NO oxidation efficiency at 250 ℃. Respectively, 1155.2 μg g−1 Hg0 adsorption capacity and 92.9 μmol g−1 NOx adsorption capacity over Co3Cu1 catalyst were measured by Hg0-TPD and NOx-TPD. The largest BET specific surface area of Co3Cu1 catalyst was obtained, reaching 26.2 m2 g−1. And H2-TPR demonstrated that the first reduction peak temperature (192 ℃) of Co3Cu1 catalyst was much lower than that of other catalysts. O2-TPD illustrated that the oxygen storage capacity and oxygen mobility ability of Co3Cu1 catalyst were higher than that of other catalysts. These results were consistent with the results of Hg0 and NO oxidation activity tests. In addition, in-situ DRIFTS spectra of NO adsorption indicated that the band at 1390 cm−1 over Co3Cu1 catalyst disappeared after the pretreatment of Hg0. And the transient experiments of Hg0 adsorption suggested that Hg0 could also be extruded from the surface of Co3Cu1 catalyst after the introduction of NO. It was speculated that there might be competitive adsorption between Hg0 and NO over Co3Cu1 catalyst. Finally, the XPS characterization demonstrated that the Oα and the redox cycle of Co3+ + Cu+ ↔ Co2+ + Cu2+ were involved in Hg0-NO simultaneous oxidation. The Co3Cu1 catalyst was an excellent candidate for Hg0-NO oxidation reaction.

Electrical Wiring of Malarial Parasite Intermediate Hematin on a Tailored N-Doped Carbon Nanomaterial Surface and Its Bioelectrocatalytic Hydrogen Peroxide Reduction and Sensing.

Hematin, an iron-containing porphyrin compound, plays a crucial role in various biological processes, including oxygen transport, storage, and functionality of the malarial parasite. Specifically, hematin-Fe interacts with the nitrogen atom of antimalarial drugs, forming an intermediate step crucial for their function. The electron transfer functionality of hematin in biological systems has been scarcely investigated. In this study, we developed a biomimicking electrical wiring of hematin-Fe with a model N-drug system, represented as {hematin-Fe---N-drug}. We achieved this by immobilizing hematin on a multiwalled carbon nanotube (MWCNT)/N-graphene quantum dot (N-GQD) modified electrode (MWCNT/N-GQD@Hemat). N-GQD serves as a model molecular drug system containing nitrogen atoms to mimic the {hematin-Fe---N-drug} interaction. The prepared bioelectrode exhibited a distinct redox peak at a measured potential (E1/2) of -0.410 V vs Ag/AgCl, accompanied by a surface excess value of 3.54 × 10-9 mol cm-2. This observation contrasts significantly with the weak or electroinactive electrochemical responses documented in literature-based hematin systems. We performed a comprehensive set of physicochemical and electrochemical characterizations on the MWCNT/N-GQD@Hemat system, employing techniques including FESEM, TEM, Raman spectroscopy, IR spectroscopy, and AFM. To evaluate the biomimetic electrode's electroactivity, we investigated the selective-mediated reduction of H2O2 as a model system. As an important aspect of our research, we demonstrated the use of scanning electrochemical microscopy to visualize the in situ electron transfer reaction of the biomimicking electrode. In an independent study, we showed enzyme-less electrocatalytic reduction and selective electrocatalytic sensing of H2O2 with a detection limit of 319 nM. We achieved this using a batch injection analysis-coupled disposable screen-printed electrode system in physiological solution.

New method for the preparation of hierarchical nanotube K0.3xMnxCe1-xOδ catalysts and their excellent catalytic performance for soot combustion

A series of nanofibrous K-Mn-Ce composite oxide catalysts were prepared via a centrifugal spinning method for the first time, and their physicochemical properties were studied. The prepared K0.3xMnxCe1-xOδ metal oxide catalyst, which is a composite of CeO2 and cryptopotassium manganese-type K2-xMn8O16, exhibits a hierarchical nanotube structure with uniform nanoneedles on its surface. During the process of soot oxidation, CeO2 utilizes its unique oxygen storage and release capacity to supply oxygen species. Simultaneously, the excellent redox properties of K2-xMn8O16 effectively promote valence cycling of the active components and produce more active oxygen species. This synergistic effect effectively enhances the intrinsic activity of the catalysts. Among the prepared catalysts, K0.15Mn0.5Ce0.5Oδ exhibits the highest catalytic performance, with 10% (T10), 50% (T50), and 90% (T90) soot conversion temperatures of 267 °C, 309 °C, and 338 °C, respectively, and shows good stability and water and sulfur resistance. Based on their simple preparation, low cost, and good catalytic performance, K0.3xMnxCe1-xOδ composite metal oxide catalysts have good potential in catalytic soot combustion applications.

Improving storage performance and lattice oxygen stability of single crystal LiNi0.925Co0.03Mn0.045O2 by integrating utilization of surface residual lithium and lattice modulation

In lithium-ion batteries, Ni-rich single crystal cathode material (Ni > 90 %) is a promising cathode material, but it has not yet been put into commercial application due to defects such as structural degradation, air sensitivity and thermal instability. In this paper, the residual lithium compounds on the surface of high-nickel materials are not useless. Li3PO4 coated and Mg2+ doped single crystal cathode materials (SC-NCM-MP) were successfully prepared by precisely controlling the amount of MgHPO4 by titration and reacting with lithium compounds left on the surface of LiNi0.925Co0.03Mn0.045O2 (SC-NCM) cathode materials. The SC-NCM-MP samples exhibit better lattice oxygen stability, Li-ion mobility, storage performance and electrochemical performance, with a retention of 89.36 % after 100 cycles, which is much higher than 79.78 % of SC-NCM.

A versatile delivery vehicle for cellular oxygen and fuels or metabolic sensor? A review and perspective on the functions of myoglobin.

A canonical view of the primary physiological function of myoglobin (Mb) is that it is an oxygen (O2) storage protein supporting mitochondrial oxidative phosphorylation, especially as the tissue O2 partial pressure (Po2) drops and Mb off-loads O2. Besides O2 storage/transport, recent findings support functions for Mb in lipid trafficking and sequestration, interacting with cellular glycolytic metabolites such as lactate (LAC) and pyruvate (PYR), and "ectopic" expression in some types of cancer cells and in brown adipose tissue (BAT). Data from Mb knockout (Mb-/-) mice and biochemical models suggest additional metabolic roles for Mb, especially regulation of nitric oxide (NO) pools, modulation of BAT bioenergetics, thermogenesis, and lipid storage phenotypes. From these and other findings in the literature over many decades, Mb's function is not confined to delivering O2 in support of oxidative phosphorylation but may serve as an O2 sensor that modulates intracellular Po2- and NO-responsive molecular signaling pathways. This paradigm reflects a fundamental change in how oxidative metabolism and cell regulation are viewed in Mb-expressing cells such as skeletal muscle, heart, brown adipocytes, and select cancer cells. Here, we review historic and emerging views related to the physiological roles for Mb and present working models illustrating the possible importance of interactions between Mb, gases, and small-molecule metabolites in regulation of cell signaling and bioenergetics.

The effect of the oxygen storage material on a three-way catalyst spatio-temporally resolved with Spaci-MS

A methodology that allows the estimation of the stored oxygen (oxygen storage capacity (OSC)) along the TWC catalyst length by spatio-temporally resolving the O2 profiles during rich to lean cycle conditions with the use of the Spaci-MS technique has been developed. As a case study, the effect of the presence of mixed cerium-zirconium oxide as oxygen storage material has been investigated. The oxygen storage capacity for the TWC containing Ce material was much higher than without. The study also explores the reaction pathways typical of TWC along the catalyst coordinates by spatio-temporally resolving O2, H2, CO, and NO, as well as the related products and intermediates providing important understanding on, for example, the water-gas shift reaction leading to H2 production and how they develop differently depending on the OSM (oxygen storage material) in the catalyst. H2 production occurs closer to the front of the TWC length in the case of the catalyst without Ce, and results in an earlier production of undesired NH3 from NO reaction with H2. However, more N2O has been observed for the catalyst with Ce, which suggests the catalyst composition could be optimised to minimize overall secondary emissions.

Study on performance and water deactivation mechanism of low-temperature denitrification catalyst in high-humidity flue gas

To address water poisoning issues of Selective Catalytic Reduction (SCR) denitrification catalysts in high-humidity flue gas, this study synthesized catalysts including Co–Mn/TiO2, Co–Mn–Ce/TiO2, Co–Mn–Ce/TiO2–Si, and Co–Mn–Ce/TiO2 (stearic acid). The activity of the catalysts at low temperatures and high humidity (140–180 °C, 0–35 vol%) was evaluated. Furthermore, the characterization of the most effective of these (the Co–Mn–Ce/TiO2 (stearic acid) catalyst) was performed. The results revealed distinct mechanisms of water poisoning under high- and low-humidity conditions. Under high humidity, the dissolution of water molecules affected the catalyst structure and thereby, resulted in reduced dispersibility of the active components. Conversely, at low humidity, the dissolution effect was relatively marginal, which resulted in a more stable catalyst structure. High-humidity flue gas reduced the catalyst acidity and thereby, hindered NH3 adsorption. Meanwhile, low-humidity flue gas had a lesser impact on the catalyst. High-humidity flue gas hinders the conversion of Co ions in Co–Mn–Ce/TiO2（stearic acid ) to higher oxidation states and reduced Ce4+ to Ce3+. This resulted in decreased Mn4+ on the catalyst surface and reduced chemisorbed oxygen (Oa). This, in turn, affected the adsorption and storage of oxygen by the catalyst.

Cryogenic Modules for Synergistic O2 Generation and CO2 Retention in Closed-Circuit Escape Respirators

Since 2018, NASA and the National Institute for Occupational Safety and Health (NIOSH) have been developing a liquid oxygen storage module (LOXSM) based on the NASA patent-pending Cryogenic Flux Capacitor (CFC) technology. LOXSM’s could potentially replace the gaseous or chemical-based oxygen supply in current closed-circuit escape respirators (CCER), with reducing CCER size being a primary goal. By virtue of the CFC functionality, cryogenic oxygen stored within the LOXSM is released in response to heat input, ideally from the breathing loop. Prior efforts focused on the oxygen storage potential of silica aerogel materials that the CFC utilizes, and were previously reported. Current work explored the LOXSM’s potential to remove and retain CO2 produced by the CCER user, in conjunction with oxygen generation, creating a synergy that may be exploited to reduce or eliminate the chemical CO2 absorber used in current CCERs. A test program for determining CO2 retention is presented, as well as the evolution of LOXSM prototypes. Testing showed that it is possible to completely remove CO2 out of an effluent stream at the flowrate required for the capacity of the CCER for an appreciable time, and that the LOXSM prototype design progression had a positive effect on that duration.

Myoglobin: A versatile age-old oxygen carrying hemoprotein and its emerging role in metabolite regulation in diverse tissues

Myoglobin (Mb) is an age-old heme containing cytoplasmic protein primarily expressed in heart and skeletal muscles, which is capable of rapid release of O2 during the periods of hypoxia or anoxia. The canonical view of the primary physiological function of Mb is that it is a tissue oxygen (O2) storage protein supporting mitochondrial oxidative phosphorylation especially as the tissue O2 partial pressure ( pO2) drops and Mb increasingly offloads O2. For the past 50 years, many investigators are constantly exploring wide-range of physiological functions and metabolic regulation activities of Mb. Advanced genetic engineering tools and molecular techniques revealed important new insights and provided additional functions of Mb. However, accumulating evidence indicates that this paradigm is too narrow, especially in light of recent findings supporting plausible functions for Mb in lipid traffcking and sequestration, binding of small molecules such as lactate (LAC), pyruvate (PYR), glucose (GLU), polyamines, and glutathione (GSH), and “ectopic” expression in some types of cancer cells. Data from Mb knockout mice (Mb−/−) and biochemical models suggest additional metabolic roles for Mb, especially regulation of nitric oxide (NO) pools and modulation of thermogenic brown adipose tissue (BAT) bioenergetics and lipid storage phenotypes. From these and other findings in the literature over many decades, it may be contemplated that the primary role for Mb under most conditions for Mb besides delivering O2 in support of oxidative phosphorylation, but also serve as an O2-sensor that modulates intracellular O2- and NO-responsive molecular signaling pathways. This paradigm shift reflect a fundamental change in how oxidative metabolism and cell regulation are viewed in Mb-expressing cells such as skeletal muscle, heart, brown adipocytes, and select cancer cells. Herein, we present historic and emerging views related to the physiological roles for Mb, and working models illustrating the possible importance of interactions between Mb, gases, and small molecule metabolites in regulation of cell signaling and bioenergetics. USDA-ARS project 6026-51000-010-06S, Sturgis Foundation Grant AWD00054750 and ACRI-ABI Investigator Initiated Grant Award GR037175-4450S ABI. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Evolution of the peroxiredoxin gene family: an antioxidant enzyme in the context of hypoxia-induced by aquatic mammals dives

Peroxiredoxins are a group of antioxidant enzymes that play a crucial role in eliminating hydrogen peroxide (H2O2) produced during cellular metabolism. In conditions such as tissue ischemia/reperfusion, H2O2 production is heightened. This scenario is recurrent in aquatic mammals, such as cetaceans and pinnipeds, when they perform breath-hold dives that lead to depletion of oxygen stores and cell hypoxia due to prolonged submersion. In such circumstances, peroxiredoxins are essential for regulating metabolism and preventing oxidative damage. Thus, our objective was to investigate evolutionary patterns of the peroxiredoxin gene family among aquatic mammalian species. Accordingly, we identified the number of ortholog and paralog genes among mammals, examining events of gene duplication, patterns of chromosomal distribution, and adaptive selection. We found that most subtypes of peroxiredoxins are characterized by single-copy genes with minimal missing data, with PRDX1, the most highly expressed subtype found in both the nucleus and cytoplasm, exhibiting an increase in gene copies in aquatic mammals, particularly in pinnipeds. The distribution of the copies was dispersed along the genome and the majority were retrocopies of the main coding sequence with little divergence among them. We also found evidence of positive selection in the PRDX3 gene, especially in a convergent mutation among two deepest-diving species, cuvier’s beaked whale and southern elephant seal in which the amino acid had radical physical-chemical property change, possibly affecting the protein function. These results suggest that the peroxiredoxin gene family has a role in the evolution of aquatic mammals by reducing oxidative damage intrinsic to diving behavior in these species. FAPESP - São Paulo Research Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Diving into old age: exercise and aging affect cardiovascular control in a long-lived mammal, the Weddell seal

The central component of the mammalian dive response is bradycardia, which, in combination with other physiological mechanisms, conserves intrinsic oxygen stores and facilitates longer submersion. Several factors are hypothesized to affect diving heart rate ( fH) and its variability (HRV) through a shift in autonomic balance. This study aimed to elucidate how dive duration, aging, and exercise influence fH and HRV (calculated as root mean square of successive RR interval differences) of free-ranging Weddell seals ( Leptonychotes weddellii). We expected that mean dive fH and HRV would differ with dive duration, advancing age, and exercise intensity due to a shift in autonomic balance. We collected ECG data from free-ranging female Weddell seals in Erebus Bay, Antarctica (n=10 seals, n=120 dives, age range 9-25 years old). To increase the cost of transport, we affxed a “drag block” to three seals for a portion of their deployment period (n=30 dives). Linear mixed effects model selection identified the effects of dive behavior (duration and depth), seal age, and drag block presence on mean dive fH and HRV. As dive duration increased, mean dive fH decreased (F1,107=227.91, p<0.0001) while HRV increased (F1,103=84.47, p<0.0001), suggesting increased parasympathetic tone. HRV was reduced in older seals (F1,8=8.73, p=0.018), indicating attenuation of parasympathetic influence on bradycardia with advancing age. Consistent with this interpretation, HRV increased with dive duration more steeply in younger animals (age*duration: F1,103=10.31, p=0.002). When exercise effort was experimentally modified by attaching a drag block to free-ranging seals, both mean dive fH (F1,107=6.07, p=0.015) and HRV (F1,103=4.34, p=0.039) were affected; dive HRV was significantly higher when seals dove with a drag block. However, this result should be interpreted with caution until the effects of swimming effort on fH and HRV can be determined. There was a significant interaction between animal age and factors affecting cardiovascular control (age*drag: F1,107=5.16, p=0.028); mean dive fH increased with age when seals did not carry a drag block, but decreased with age when a drag block was present. Taken together, our results point to cardiovascular aging as a physiological element that could affect the foraging ability, fitness, and life history of a long-lived free-ranging mammal. Funding by the National Science Foundation (#0649609, #0440715, #2020706). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Fasting Metabolic Profiles are Cell-Autonomous in Elephant Seal Primary Muscle Cells

Northern elephant seals ( Mirounga angustirostris) undergo prolonged terrestrial fasts during energetically intensive life stages including breeding, molting, and postnatal development. Fasting-tolerant vertebrates generally extend the second phase of fasting, during which body mass declines but homeostasis is preserved through reliance on lipid fuel sources and sparing of body protein stores. In elephant seals, the postnatal fast coincides with development of the extensive body oxygen stores required to support extended breath-hold diving, as well as an increased capacity for apnea-related metabolic suppression. Studies in grizzly bears, another large-bodied fasting-tolerant mammal, have identified both serum-derived and intrinsic cellular regulation of the adipocyte metabolic phenotype. However, it is unknown whether these mechanisms extend across species, tissue, or fasting type (active vs inactive). Thus, we derived proliferative primary skeletal muscle cells (myoblasts) from weaned elephant seal pups; biopsies that yielded cells were collected at both early (~1 week) and late (~8 weeks) points in the postnatal fast. We found that total ATP production rate was greater in myoblasts collected from animals late in the fast (27% increase over early, p=0.08). Throughout the fast, myoblasts relied predominantly on glycolytic rather than oxidative ATP production (p<0.001), and this reliance increased as the fast progressed (p<0.014). Together, these data suggest that metabolic reliance is at least partially cell-autonomous in elephant seal myoblasts. KNA is supported by an NSF Graduate Research Fellowship (DGE 1752814 & 2146752) and a UC Berkeley Fellowship. JPV-M is supported by a NIH/NIGMS grant (R35GM146951). Research was funded by UC Berkeley startup funds and the Winkler Family Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

MOX-TiO2 (M=Pt, Pd, Ru) for alcoholysis reaction from furfuryl alcohol to ethyl levulinate

Simple noble metal oxides (PtOx, PdOx, RuOx) based titanium dioxide (Pt–TiO2, Pd–TiO2, Ru–TiO2) were prepared using a facile sol-gel method. The conversion of furfuryl alcohol (FAL) to ethyl levulinate (EL) was studied. Full characterizations were performed using XRD, XPS, Raman and in situ FT-IR. An in-depth study of acidic strength and sites distribution (Brønsted or Lewis) was conducted by NH3-TPD, pyridine-IR. The profiles of H2-TPR and O2-TPD suggested enhanced reducibility and optimum oxygen storage capacity in Pt–TiO2. Remarkable FAL conversion (94.4%), EL yield (89.6%) with productivity (21.3 × 103 molEL/mmolPt h) and TOF (22.5 × 103 molFAL/mmolPt h) were obtained. Metal productivity follows the order: Pt (21.3 × 103 molEL/mmolPt h) > Ru (11.5 × 103 molEL/mmolRu h) > Pd (3.6 × 103 molEL/mmolPd h). Two different reaction pathways were proposed. From computational calculations of charge density differences and Ead value, a robust electron transfer capacity was found in Pt–TiO2, as well as an advantageous FAL adsorption as compared to other catalytic systems.

Investigating the effect of oxygen vacancy on electronic, optical, thermoelectric and thermodynamic properties of CeO2 (ceria) for energy and ReRAM applications: A first-principles quantum analysis

CeO2 thin film-based devices have become hot favorite candidates for researchers due to the outstanding characteristics of ceria such as memory storage materials, high oxygen storage capacity, excellent chemical and thermal stability, high transparency in visible region and highly tunable energy band structures. Developing suitable materials for industrial uses like optoelectronic and thermoelectric devices is the primary goal of researchers in the field of renewable energy. Herein, we have investigated the optical, thermoelectric and thermodynamic properties of CeO2 and [Formula: see text] as promising candidates for energy applications using first-principles calculations. We can observe significant absorption of incident photons by CeO2 and [Formula: see text] near UV region. The highest peaks of the [Formula: see text] are present around 3.7[Formula: see text]eV in spin [Formula: see text] channel, however, in spin [Formula: see text] channel, the highest peaks of the [Formula: see text] are present around 3.5[Formula: see text]eV. The most intense peaks that emerge are due to the transitions of O[[Formula: see text]] to Ce [[Formula: see text]]. The investigated values of [Formula: see text] reveal that CeO2 and [Formula: see text] are active optical materials. CeO2 and [Formula: see text] reflect a negligible number of incident photons ([Formula: see text]%) in the entire energy range. The positive value of the S shows that the CeO2 under study is p-type semiconductor, while [Formula: see text] is n-type semiconductor as its S value is negative. The S values for CeO2 are close to the established standard. As a result, CeO2 is a viable thermoelectric material for use in devices. The figure of merit (ZT) spectra reveals that CeO2 ([Formula: see text]) is a more capable candidate for thermoelectric materials compared to [Formula: see text] ([Formula: see text]). The investigated thermodynamic parameters reveal that CeO2 and [Formula: see text] are dynamically stable compounds.

Mn-Based Mullites for Environmental and Energy Applications.

Mn-based mullite oxides AMn2O5 (A = lanthanide, Y, Bi) is a novel type of ternary catalyst in terms of their electronic and geometric structures. The coexistence of pyramid Mn3+-O and octahedral Mn4+-O makes the d-orbital selectively active toward various catalytic reactions. The alternative edge- and corner-sharing stacking configuration constructs the confined active sites and abundant active oxygen species. As a result, they tend to show superior catalytic behaviors and thus gain great attention in environmental treatment and energy conversion and storage. In environmental applications, Mn-based mullites have been demonstrated to be highly active toward low-temperature oxidization of CO, NO, volatile organic compounds (VOCs), etc. Recent research further shows that mullites decompose O3 and ozonize VOCs from -20°C to room temperature. Moreover, mullites enhance oxygen reduction reactions (ORR) and sulfur reduction reactions (SRR), critical kinetic steps in air-battery and Li-S batteries, respectively. Their distinctive structures also facilitate applications in gas-sensitive sensing, ionic conduction, high mobility dielectrics, oxygen storage, piezoelectricity, dehydration, H2O2 decomposition, and beyond. A comprehensive review from basic physicochemical properties to application certainly not only gains a full picture of mullite oxides but also provides new insights into designing heterogeneous catalysts.

Mechanistic insights into methane total oxidation over Cu/Hydroxyapatite catalyst synthesized with β-Cyclodextrin assistance

The total oxidation of methane (CH4), a highly stable alkane volatile organic compound (VOC), using low-cost Cu-based catalysts, has garnered considerable attention. Nonetheless, challenges such as Cu particle agglomeration and the lack of consensus on mechanism of CH4 total oxidation over Cu-based catalysts remain. In this work, β-cyclodextrin (βCD) was introduced during Cu/hydroxyapatite catalyst (βCD-Cu/HAP) preparation, and its catalytic performance in CH4 total oxidation was compared with the Cu/HAP catalyst. Both materials were prepared using the wet impregnation method and thoroughly characterized. It was found that utilization of βCD, which decomposed during calcination, led to smaller Cu particle size (from 61 to 34 nm) and better Cu dispersion (from 1.9 to 3.5 %), resulting in an enhancement of the catalyst reduction properties. Additionally, the βCD-Cu/HAP catalyst possessed a higher oxygen storage capacity, demonstrating its superior ability to replenish the oxygen vacancies. The βCD-Cu/HAP catalyst activity was double that of the original Cu/HAP catalyst with a 20kJmol-1 lower activation energy, as determined by fitting the initial reaction rate to a power-law model. Further, Langmuir–Hinshelwood (LH), Eley–Rideal (ER), and Mars–van Krevelen (MVK) type rate expressions were regressed to the experimental data. After statistical and physico-chemical assessments, the MVK mechanism involving two oxidized sites and one reduced site with H2O adsorption on oxidized sites was identified as the most appropriate model for describing the experimental data. These findings offer an enhanced understanding of CH4 total oxidation, guiding the development of efficient, low-cost catalysts for this reaction. Environmental ImplicationVolatile organic compounds (VOCs) pose significant environmental and health issues due to their toxicity and widespread sources. Among VOCs, alkane contribute to a large proportion of the VOCs emitted, with light alkanes being particularly challenging to mitigate due to their high stability. Methane, the most stable light alkanes, is the focus of this study. Catalytic oxidation technology offers a promising solution for VOC mitigation. In our work, we conducted a mechanistic investigation of methane total oxidation, aiming at deepening our understanding of catalytic oxidation of light alkanes, thereby contributing to substantial environmental benefits.

Abundance of Low-Energy Oxygen Vacancy Pairs Dictates the Catalytic Performance of Cerium-Stabilized Zirconia.

Cerium-stabilized zirconia (Ce1-xZrxOy, CZO) is renowned for its superior oxygen storage capacity (OSC), a key property long believed to be beneficial to catalytic oxidation reactions. However, 50% Ce-containing CZO recorded with the highest OSC has disappointingly poor performance in catalytic oxidation reactions compared to those with higher Ce contents but lower OSC ability. Here, we employ global neural network (G-NN)-based potential energy surface exploration methods to establish the first ternary phase diagram for bulk structures of CZO, which identifies three critical compositions of CZO, namely, 50, 60, and 80% Ce-containing CZO that are thermodynamically stable under typical synthetic conditions. 50% Ce-containing CZO, although having the highest OSC, exhibits the lowest O vacancy (Ov) diffusion rate. By contrast, 60% Ce-containing CZO, despite lower OSC (33.3% OSC compared to that of 50% Ce-containing CZO), reaches the highest Ov diffusion ability and thus offers the highest CO oxidation catalytic performance. The physical origin of the high performance of 60% Ce-containing CZO is the abundance of energetically favorable Ov pairs along the ⟨110⟩ direction, which reduces the energy barrier of Ov diffusion in the bulk and promotes O2 activation on the surface. Our results clarify the long-standing puzzles on CZO and point out that 60% Ce-containing CZO is the most desirable composition for typical CZO applications.

Oxygen Storage Incorporated Into Net Power and the Allam–Fetvedt Oxy-Fuel sCO2 Power Cycle—Techno-Economic Analysis

Abstract With the planned future reliance on variable renewable energy, the ability to store energy for prolonged time periods will be required to reduce the disruption of market fluctuations. This paper presents a method to analyze a hybrid liquid-oxygen (LOx) storage/direct-fired supercritical carbon dioxide (sCO2) power cycle and optimize the economic performance over a diverse range of scenarios. The system utilizes a modified version of the NET Power process to produce energy when energy demand exceeds the supply while displacing much of the cost of the air separation unit (ASU) energy requirements through cryogenic storage of oxygen. The model uses marginal cost of energy data to determine the optimal times to charge and discharge the system over a given scenario. The model then applies ramp rates and other time-dependent factors to generate an economic model for the system without storage considerations. The size of the storage system is then applied to create a realistic model of the plant operation. From the real plant operation model, the amount of energy charged and discharged, the capital expenditures (CAPEX) of each system, energy costs and revenue and other parameters can be calculated. The economic parameters are then combined to calculate the net present value (NPV) of the system for the given scenario. The model was then run through the SMPSO genetic algorithm in Python for a variety of geographic regions and large-scale scenarios (high solar penetration) to maximize the NPV based on multiple parameters for each subsystem. The LOx storage requirements will also be discussed.