Search Results (187)

Herein, α-MnO₂-supported Pt-Pd bimetal (xPd-yPt/α-MnO₂; x and y are the weight loadings (wt%) of Pd and Pt, respectively; x = 0, 0.23, 0.47, 0.93, and 0.92 wt%; and y = 0.91, 0.21, 0.46, 0.89, and 0 wt%) catalysts were prepared using the polyvinyl alcohol-protected NaBH₄ reduction method. The physicochemical properties of the catalysts were determined by means of various techniques and their catalytic activities for toluene oxidation were evaluated. It was found that among the xPd-yPt/α-MnO₂ samples, 0.93Pd-0.89Pt/α-MnO₂ showed the best catalytic performance, with the toluene oxidation rate at 156 °C (r_cat) and space velocity = 60,000 mL/(g h) being 6.34 × 10⁻⁴ mol/(g s), much higher than that of 0.91Pt/α-MnO₂ (1.31 × 10⁻⁴ mol/(g s)) and that of 0.92Pd/α-MnO₂ (6.13 × 10⁻⁵ mol/(g s)) at the same temperature. The supported Pd-Pt bimetallic catalysts possessed higher Mn³⁺/Mn⁴⁺ and O_ads/O_latt molar ratios, which favored the enhancement in catalytic activity of the supported Pd-Pt bimetallic catalysts. Furthermore, the 0.47Pd-0.46Pt/α-MnO₂ sample showed better resistance to sulfur dioxide poisoning. The partial deactivation of 0.47Pd-0.46Pt/α-MnO₂ was attributed to the formation of sulfate species on the sample surface, which covered the active site of the sample, thus decreasing its toluene oxidation activity. In addition, the in situ DRIFTS results demonstrated that benzaldehyde and benzoate were the intermediate products of toluene oxidation. Full article

This study investigated the effect of adding superhard ReB₂ to atmospheric plasma sprayed (APS) coatings based on 60 wt% Al₂O₃ and 40 wt% ZrO₂. The amorphous phases commonly present in such coatings are known to impair their performance. ReB₂ was introduced as a crystallization nucleus due to its high melting point. ReB₂ decomposes in the presence of moisture and oxygen into H₃BO₃, ReO₃, HBO₂, and HReO₄. ReB₂ was encapsulated with Al₂O₃ via metallothermic synthesis to improve moisture stability, yielding a powder with d₉₀ = 15.1 μm. After milling, it was added at 20 wt% to the Al₂O₃-ZrO₂ feedstock. Agglomeration parameters were optimized, and coatings were deposited under varying APS conditions onto 316L steel substrates with a NiAl bond coat. In the coating with the highest ReB₂ content, the identified phases included ReB₂ (2.6 wt%), Re (0.8 wt%), α-Al₂O₃ (30.9 wt%), η-Al₂O₃ (32.4 wt%), and monoclinic and tetragonal ZrO₂. The nanohardness of the coating, measured using a Vickers indenter at 96 mN and calculated via the Oliver–Pharr method, was 9.2 ± 1.0 GPa. High abrasion resistance was obtained for the coating with a higher content of η-Al₂O₃ (48.7 wt%). The coefficient of friction, determined using a ball-on-disc test with a corundum ball, was 0.798 ± 0.03. After 15 months, the formation of (H₃O)(ReO₄) was observed, suggesting initial moisture-induced changes. The results confirm that Al₂O₃-encapsulated ReB₂ can enhance phase stability and crystallinity in APS coatings. Full article

The new mineral achyrophanite (K,Na)₃(Fe³⁺,Ti,Al,Mg)₅O₂(AsO₄)₅ was found in high-temperature sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, hematite, alluaudite-group arsenates (badalovite, calciojohillerite, johillerite, nickenichite, hatertite, and khrenovite), ozerovaite, pansnerite, arsenatrotitanite, yurmarinite, svabite, tilasite, katiarsite, yurgensonite, As-bearing sanidine, anhydrite, rutile, cassiterite, and pseudobrookite. Achyrophanite occurs as long-prismatic to acicular or, rarer, tabular crystals up to 0.02 × 0.2 × 1.5 mm, which form parallel, radiating, bush-like, or chaotic aggregates up to 3 mm across. It is transparent, straw-yellow to golden yellow, with strong vitreous luster. The mineral is brittle, with (001) perfect cleavage. D_calc is 3.814 g cm^–3. Achyrophanite is optically biaxial (+), α = 1.823(7), β = 1.840(7), γ = 1.895(7) (589 nm), 2V (meas.) = 60(10)°. Chemical composition (wt.%, electron microprobe) is: Na₂O 3.68, K₂O 9.32, CaO 0.38, MgO 1.37, MnO 0.08, CuO 0.82, ZnO 0.48, Al₂O₃ 2.09, Fe₂O₃ 20.42, SiO₂ 0.12, TiO₂ 7.35, P₂O₅ 0.14, V₂O₅ 0.33, As₂O₅ 51.88, SO₃ 1.04, and total 99.40. The empirical formula calculated based on 22 O apfu is Na_1.29K_2.15Ca_0.07Mg_0.34Mn_0.01Cu_0.11Zn_0.06Al_0.44Fe³⁺_2.77Ti_1.00Si_0.02P_0.02S_0.14V_0.04As_4.90O₂₂. Achyrophanite is orthorhombic, space group P222₁, a = 6.5824(2), b = 13.2488(4), c = 10.7613(3) Å, V = 938.48(5) ų and Z = 2. The strongest reflections of the PXRD pattern [d,Å(I)(hkl)] are 5.615(59)(101), 4.174(42)(022), 3.669(31)(130), 3.148(33)(103), 2.852(43)(141), 2.814(100)(042, 202), 2.689(29)(004), and 2.237(28)(152). The crystal structure of achyrophanite (solved from single-crystal XRD data, R = 4.47%) is unique. It is based on the octahedral-tetrahedral M-T-O pseudo-framework (M = Fe³⁺ with admixed Ti, Al, Mg, Na; T = As⁵⁺). Large-cation A sites (A = K, Na) are located in the channels of the pseudo-framework. The achyrophanite structure can be described as stuffed, with the defect heteropolyhedral pseudo-framework derivative of the orthorhombic Fe³⁺AsO₄ archetype. The mineral is named from the Greek άχυρον, straw, and φαίνομαι, to appear, in allusion to its typical straw-yellow color and long prismatic habit of crystals. Full article

Nitrogen oxides (NO_x), harmful pollutants primarily from fossil fuel combustion, pose significant environmental and health risks. Among mitigation technologies, NH₃-SCR is widely adopted due to its high efficiency and industrial viability. MnO₂-based catalysts, particularly α-MnO₂, have gained attention for low-temperature NH₃-SCR owing to their redox properties, low-temperature activity, and environmental compatibility. In this study, α-MnO₂ catalysts with tunable oxygen vacancy concentrations were synthesized by varying calcination atmospheres. Compared to α-MnO₂-Air, the oxygen vacancy-rich α-MnO₂-N₂ exhibited stronger acidity, enhanced redox properties, and superior NH₃/NO adsorption and activation, achieving 98% NO conversion at 125–250 °C. Oxygen vacancies promoted NH₃ adsorption on Lewis/Brønsted acid sites, facilitating -NH₂ intermediate formation, while enhancing NO oxidation to reactive nitrates. In situ DRIFTS revealed a dual E-R and L-H reaction pathway, with oxygen vacancies crucial for NO activation, intermediate formation, and N₂ generation. These findings underscore the importance of oxygen vacancy engineering in optimizing Mn-based SCR catalysts. Full article

MnO₂ nanostructures were successfully synthesized via the reduction of KMnO₄ solutions using the gliding arc plasma (Plasma Glidarc) approach. Here, we highlight the effect of different plasmagenic gases, such as moist air (atmospheric air), dry air, nitrogen (N₂) or oxygen (O₂). The obtained materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nitrogen physisorption and scanning electron microscopy (SEM). The crystalline structures of obtained MnO₂ polymorphs are mainly γ-MnO₂ and α-MnO₂, regardless of the feeding gas. The main reactive species, in addition to nitrogenous species like NO· radical generated with moist air, dry air or N₂ gas, other oxygenated species such as H₂O₂ (E°(O₂/H₂O₂) = 0.69 V) are produced with O₂ able to reduce KMnO₄ solution (E°(KMnO₄/MnO₂) = 1.70 V). Helium gas did not allow for the plasma reduction of the KMnO₄ solution, even after 60 min of exposure. Furthermore, gas humidification did not significantly affect the precipitation time or the properties of plasma-synthesized MnO₂. Atmospheric humidified air appears to be the best plasmagenic gas, as it allows for a shorter synthesis time and leads to a large specific surface area. All plasma-synthesized MnO₂ showed good activity during the catalytic oxidation of benzene. The use of different MnO₂ polymorphs (α-, δ- and γ-MnO₂) showed that, in addition to the specific surface area, the crystalline structure significantly affects the catalytic oxidation of benzene. K⁺ species inserted within the MnO₂ structure allow for their stability during the catalytic process. This work highlights the possibility to use different plasmagenic gases to prepare MnO₂ nanostructures through plasma glidarc for the catalytic oxidation of benzene. Full article

The Co-CuCoMnO_x coatings with varying proportions were prepared and investigated to develop a novel metal–ceramic solar selective absorption coating employed at high temperature. The CuCoMnO_x powders were synthesized using the solid-phase reaction method. Subsequently, Co-CuCoMnO_x coatings were deposited on the surface of 316L steels utilizing the atmospheric plasma spraying (APS) technique. The results showed that the synthesized CuCoMnO_x powders were mainly composed of two phases, which were Cu_1.5Mn_1.5O₄ and MnCo₂O₄. The CuCoMnO_x powders had a solar absorptance of 0.929 and an infrared emittance of 0.862, which was considered a good solar absorbent. The synthesized Co-CuCoMnO_x coating had a typical thermal spray layered stacking structure. The chemical phases of the coatings were mainly Co, CoO, and CoCuMnO_x. Due to the addition of CuCoMnO_x inhibiting the oxidation of Co during the thermal spraying process, the 95Co-5CuCoMnO_x (wt%) coating exhibited the optimal quality factor (α/ε) of 2.184, with a solar absorptance α of 0.808 and an infrared emittance ε of 0.370, respectively. Moreover, this specific coating demonstrated a good thermal stability for up to 3 h when exposed to an atmospheric environment at 450 °C. The results indicate its significant potential for high-temperature solar selective absorption coating. Full article

Five requeijão samples, classified as Brazilian cream cheeses, were developed: one control (without guabiroba pulp (Campomanesia xanthocarpa O. Berg) and four with 5, 10, 15, and 20% (m/m) guabiroba pulp. They were evaluated for pH, water activity (aw), color, texture, multi-mineral composition, carotenoid content, and microstructure. The addition of guabiroba pulp reduced pH and maintained Aw. The samples with 5%, 10%, 15%, and 20% guabiroba pulp presented a yellow–reddish coloration. The formulation with 5% had the lowest values of firmness, resilience, texture, and spreadability. From 10% onwards, an increase in cohesiveness and a reduction in creaminess were observed. The sample with 15% presented better spreadability, while the 20% sample had adhesiveness similar to the control. No traces of Al, As, Cd, Co, Cr, Cu, Fe, Mn, Pb, or Se were detected. The detected elements, in descending order, were Na, Ca, P, S, K, Mg, Sr, and Zn. β-carotene was predominant, with guabiroba pulp enhancing α-carotene, β-carotene, β-cryptoxanthin, and λ-carotene levels, especially at 20% pulp. Microstructure analysis by scanning electron microscopy (SEM) showed no significant differences. These findings highlight the potential of guabiroba pulp as a functional ingredient in requeijão, enhancing its carotenoid profile while maintaining desirable textural and physicochemical properties. Full article

Solar power generation systems, recognized for their high energy quality and environmental benefits, require efficient energy storage to ensure stable grid integration and reduce reliance on fossil fuels. Thermochemical energy storage (TCS) using metal oxides, such as the Mn₂O₃/Mn₃O₄ redox system, offers advantages like high energy density, wide temperature range, and stability, making it ideal for solar power applications. This study investigates Mn₃O₄ and Mn₂O₃ as initial reactants, analyzing reaction temperature range, rate, conversion efficiency, and cyclic performance via synchronous thermal analysis. Microstructural characterization was performed using XRD, SEM, BET, XPS, nanoparticle size, and zeta potential measurements. The results show that Mn₃O₄ reversibly converts to Mn₂O₃ with over 100% conversion efficiency over five cycles with 3.3% weight loss, indicating stable performance. Mn₃O₄ oxidation follows Arrhenius’ Law below 700 °C but deviates at higher temperatures. The oxidation mechanism function is G(α) = α and f(α) = 1, with an activation energy of 20.47 kJ/mol and a pre-exponential factor of 0.268/s. Mn₂O₃ synthesized via ammonia precipitation exhibits reversible redox behavior with 3.3% weight loss but samples from low-concentration precursors show poor cyclic performance. The reduction reaction of Mn₂O₃ has an activation energy of 249.87 kJ/mol. By investigating the Mn₂O₃/Mn₃O₄ redox system for TCS, this study advances its practical integration into solar thermal power systems and offers critical guidance for developing scalable, low-carbon energy storage technologies. These findings can support Sustainable Development Goals (SDGs) by advancing renewable energy storage technologies, reducing carbon emissions, and promoting the integration of solar power into sustainable energy grids. Full article

The synthesis of nitrate (NO₃⁻) via electrocatalytic nitric oxide oxidation reaction (NOOR) is a green and efficient strategy for nitrogen fixation, which has great advantages over conventional nitrate synthesis. Notably, it also presents a promising solution for the remediation of NO pollutants. In this study, the structure–performance correlations of α-, β-, and δ-MnO₂ catalysts were investigated. These three polymorphs of MnO₂ exhibited disparate surface chemistries, NO adsorption capabilities, and NOOR catalytic activities. In a 1.0 M KOH electrolyte, α-MnO₂, characterized by its large-sized (2 × 2) one-dimensional tunnel structure, demonstrated the most outstanding NOOR catalytic performance, which achieved a remarkable NO₃⁻ yield of 665.2 mg·h⁻¹·mg_cat⁻¹ at a potential of 1.9 V, along with excellent stability and durability. Furthermore, a Zn-NO system was constructed, employing α-MnO₂ as the anode and a Zn plate as the cathode. This innovative setup integrated an energy storage system with NO electrochemical capture, yielding a NO₃⁻ production rate of 265.5 mg·h⁻¹·mg_cat⁻¹. The density functional theory calculations confirm the NO adsorption performance and catalytic activity of three different crystal forms of MnO₂. Full article

A high-activity, low-cost, and easy-to-prepare monolithic catalyst is crucial for the industrial catalytic combustion of volatile organic compounds (VOCs) in a cost-effective manner. In this study, a highly efficient monolithic catalyst, designated as 4GM/COR, was developed by loading 4% graphene-doped α-MnO₂ (4GM) catalyst onto pre-etched cordierite (COR) blocks using a straightforward “ball-milling-assisted impregnation” method. The anchoring force of the cordierite pores, generated through oxalic acid etching, enables the uniform and robust loading of powdered 4GM onto COR, preventing detachment under high temperatures or high gas flow rates. The loading rate, specific surface area, and concentrations of Mn³⁺ and surface-lattice and absorbed oxygen species in the monolithic catalyst increase with impregnation times from 2 to 4, indicating that catalytic activity is optimized through repeated impregnation. Catalytic performance tests demonstrated that the 4-4GM/COR exhibited the highest activity, achieving 90% degradation of toluene at 200 °C under both dry and humid (relative humidity is 85%) conditions. Furthermore, the 4-4GM/COR maintains high catalytic stability and activity even at a large GHSV of 6000 h⁻¹. To conclude, the 4-4GM/COR monolithic catalyst developed in this study not only represents a promising option for industrial applications but also serves as an important reference for the synthesis of monolithic catalysts. Full article

MnO₂ catalysts are recognized as highly efficient materials for ozone decomposition at room temperature. However, the conventional preparation methods, such as the hydrothermal method, typically require critical conditions (100–200 °C for 6–48 h). Moreover, the prepared catalysts are almost powders, which makes them difficult to apply as monolithic catalysts. In this work, a simple pH-adjusted method was developed to in situ prepare MnO₂ with different crystal phases (α, amorphous, and δ) under ambient conditions. XRD analysis revealed that decreasing the pH from 13 to 3 induced a gradual phase transformation from δ-MnO₂ to amorphous MnO₂, while the α-phase appeared at pH = 1.5. The combination of XPS and O₂-TPD results shows that amorphous MnO₂ exhibited the lowest average oxidation state (AOS) and highest oxygen vacancy concentration. The optimized amorphous MnO₂ catalyst (Cat. 2) achieved the highest ozone removal efficiency of 98% with a high relative humidity of 90%. Furthermore, in situ DRIFTS experiments further demonstrated that the prepared Cat. 2 maintained minimal OH accumulation under humid conditions, confirming its excellent water resistance. Finally, the preparation method of amorphous MnO₂ was effectively applied to cordierite honeycomb carrier (CHC). The a(amorphous)-MnO₂/CHC catalyst module (100 mm × 100 mm × 20 mm) showed stable ozone removal efficiency of 60% during a 60 h evaluation in an air duct (O₃: 400 ± 30 ppb, T: 25 ± 5 °C, gas velocity: 1 m s⁻¹). This study innovatively developed a simple pH-adjusted method to prepare MnO₂ with different crystal phases under ambient conditions and successfully applied it to the cordierite honeycomb carrier for monolithic catalyst development. Full article

Zinc-ion batteries (ZIBs) are an ideal choice for large-scale energy storage due to their high safety, environmental friendliness, and low cost. However, their performance is constrained by challenges related to cathode materials, such as poor conductivity, dissolution of active materials, and structural instability during cycling. In this study, α-MnO₂ cathode material with a tunnel structure was synthesized via a hydrothermal method, and MnSO₄ was introduced into the ZnSO₄ electrolyte to optimize the electrochemical performance of ZIBs. Characterizations through XRD, SEM, and BET revealed excellent crystal morphology and nanorod structures, which provided superior ion transport pathways. With the addition of MnSO₄, the discharge specific capacity of ZIBs at 0.1 A g⁻¹ was significantly improved from 172.9 mAh g⁻¹ to 263.2 mAh g⁻¹, the cycling stability was also notably enhanced, namely, after 1000 cycles with the current density of 1 mA cm⁻², the capacity settled at 50 mAh g⁻¹, which is a 47.4% increase in relation to the case of absent additive. The experimental results indicate that MnSO₄ additives effectively suppress manganese dissolution, improving the rate capability and reducing self-discharge. This study provides a novel approach to the development of high-performance aqueous zinc-ion batteries. Full article

A new molecular theory of slag suggests that complex oxides in the phase diagram are also present in liquid slag. In contrast to the ion‒molecule coexistence theory, basic oxides (CaO, MgO, MnO, FeO, etc.) in slag are considered to agglomerate in the liquid state due to their strong mutual attraction, although they are ionized (M²⁺ and O²⁻). The predicted slag structure agrees with the experimental results, and when the model is applied to the CaO-SiO₂, CaO-Al₂O₃, and CaO-SiO₂-Al₂O₃ slag systems, the calculated molar fractions of CaO, SiO₂, and Al₂O₃ ($N_{\mathrm{CaO}},N_{{\mathrm{SiO}}_2},N_{{\mathrm{Al}}_2{\mathrm{O}}_3}$) are close to the measured activities (${\alpha }_{\mathrm{CaO}},a_{{\mathrm{SiO}}_2} \mathrm{and} a_{{\mathrm{Al}}_2{\mathrm{O}}_3}$) reported by different researchers. In the CaO-Al₂O₃ slag system, the results based on the new molecular theory are closer to the experimental values than the results of other theoretical calculations. In the practical application of the new molecular theory, the maximum concentration of each complex molecule is consistent with the position of the melting point of the same solid‒liquid components in the phase diagram, indicating that complex molecules have a strong influence on the melting point of slag. In addition, it is believed that the formation and decomposition of different complex molecules are responsible for changes in component activity in the CaO-SiO₂ and CaO-Al₂O₃ slag systems, and it is further deduced that 3CaO-SiO₂ is formed in two steps. Full article

This study evaluated the effects of three irrigation treatments (control (rain-fed plants), deficit irrigation (DI: 50% of maximum field capacity), full irrigation (FI: 100% of maximum field capacity)), and two crop-management treatments (with or without crop rotation with bean, CR, and NCR, respectively) on the plant growth and chemical composition of C. spinosum. The results indicated that deficit irrigation combined with crop rotation increased the weight of leaves per plant, followed by rain-fed plants for the same crop-management treatment. Additionally, these two factors significantly influenced the nutritional profile, free sugars, and organic acid content in a variable manner. Moreover, the control treatment and deficit irrigation increased the content of K, Na, and Mg, which are highly mobile nutrients, whereas the levels of moderately mobile nutrients such as Fe, Mn, Cu, and Zn decreased. Deficit irrigation without crop rotation significantly increased the content of total tocopherols, followed by deficit irrigation with crop rotation and full irrigation without crop rotation. The main fatty acids were α-linolenic acid (C18:3n3), followed by palmitic acid (C16:0) and linoleic acid (C18:2n6), while the control and deficit irrigation treatments combined with crop rotation increased PUFA and decreased SFA content. Furthermore, deficit irrigation and crop rotation induced the accumulation of phenolic compounds, flavonoids, and phenolic acids, especially the content of the major compounds (e.g., chicoric acid, quercetin-O-hexurunoside, and luteolin-O-hexurunoside). The leaf extracts exhibited varied antioxidant activity (assessed by TBARS and OxHLIA assays), and antimicrobial activity. On the other hand, no antifungal, antiproliferative (except for AGS cell line), hepatotoxic, or anti-inflammatory effects were recorded. In conclusion, the combination of deficit irrigation and crop rotation with bean positively affected the quality traits and the fresh weight of leaves, thus suggesting that such eco-friendly practices could have beneficial effects in the cultivation of C. spinosum plants within the context of climate-change mitigation strategies. Full article

Developing more effective gold–support synergy is essential for enhancing the catalytic performance of supported gold nanoparticles (AuNPs) in the gas-phase oxidation of ethanol to acetaldehyde (AC) at lower temperatures. This study demonstrates a significantly improved Au–support synergy achieved by copper doping in LaMO₃ (M = Mn, Fe, Co, Ni) perovskites. Among the various Au/LaMCuO₃ catalysts, Au/LaMnCuO₃ exhibited exceptional catalytic activity, achieving an AC yield of up to 91% and the highest space-time yield of 764 g_AC g_Au⁻¹ h⁻¹ at 225 °C. Notably, this catalyst showed excellent hydrothermal stability, maintaining performance for at least 100 h without significant deactivation when fed with 50% aqueous ethanol. Comprehensive characterization reveals that Cu doping facilitates the formation of surface oxygen vacancies on the Au/LaMCuO₃ catalysts and enhances Au–support interactions. The LaMnCuO₃ perovskite stabilizes the crucial Cu⁺ species, resulting in a stable Au-Mn-Cu synergy within the Au/LaMnCuO₃ catalyst, which facilitates the activation of O₂ and ethanol at lower temperatures. The optimization of the reaction conditions further improves AC productivity. Kinetic studies indicate that the cleavages of both the O-H bond and the α-C-H bond of ethanol are the rate-controlling steps. Full article