Search Results (77)

Volatile organic compounds can aggravate the atmospheric pollution and health risks due to their high toxicity and photochemical reactivity. Herein, a series of cobalt aluminate spinel catalysts with high efficiency was fabricated via a cost-efficient solvothermal method. Plentiful oxygen vacancies with negative charge were introduced adjacent to the octahedrally coordinated Co³⁺ species in CoAl₂O₄ catalysts, thereby generating the synergetic Co³⁺-oxygen vacancy (Ov) sites, which facilitated the rapid activation and migration of oxygen species. Accordingly, the superior catalytic activity was observed for 1Al-1Co even with lower cobalt due to the presence of abundant Co³⁺-Ov sites, revealing the predominant roles of synergetic sites in the toluene oxidation. Moreover, the 1Al-1Co catalyst exhibited the optimal intrinsic catalytic performance with the lowest activation energy of 161.2 kJ·mol⁻¹ and the highest specific toluene reaction rate of 3.18 × 10⁻⁵ mmol·h⁻¹·m⁻². In situ DRIFTS results further verified that oxygen vacancies and active Co³⁺ species could synergistically boost highly reactive oxygen species, which rapidly oxidize benzoate into maleic anhydride, achieving the efficient complete oxidation of toluene. Full article

Two types of coatings, NiCrAlY and NiCrAlY/YSZ, were fabricated on the surface of M247 alloy by the atmospheric plasma spraying (APS) technique. Under pure Na₂SO₄ and 25 wt.% NaCl-containing mixed salt deposits at 900 °C in air, the M247 alloy underwent rapid catastrophic corrosion. The non-protective corrosion products formed on the surface included NiO and (Ni,Co)Cr₂O₄ spinel. The hot corrosion of M247 under the pure Na₂SO₄ salt deposit followed a basic fluxing mechanism, whereas under the NaCl-containing mixed salt deposit, it was dominated by an active oxidation mechanism. During hot corrosion, the NiCrAlY coating developed a continuous, dense, and highly protective α-Al₂O₃ oxide scale on its surface, endowing it with superior hot corrosion resistance. The thermal barrier coating of NiCrAlY/YSZ exhibited the best hot corrosion resistance, attributed to the physical barrier and thermal barrier effects of the outer YSZ ceramic layer. Full article

Two cobalt alloys and one nickel alloy, containing Ta and C in similar atomic contents and either 5 or 10 wt.% Al, were cast. Their microstructures and their oxidation behaviors in air at 1200 °C over 50 h were investigated. All contained eutectic script-like TaC carbides and a dendritic matrix which was either single-phased (FCC) or double-phased (FCC + Co₃Al). The cobalt sample with 5 wt.% oxidized catastrophically, became thinner, lost all its TaC, and was covered by a thick oxide shell (outer CoO and inner mixture of CoO, CoAl₂O₄ and Ta-rich oxides). The two other alloys, Ni-based with 5 wt.% Al and Co-based with 10 wt.% Al, oxidized more slowly, with a mass gain kinetic slightly lower than that for chromia-forming alloys at 1200 °C and a continuous duplex oxide scale made of an outer MAl₂O₄ spinel and inner Al₂O₃ scales. This evidences the existence of two Al content thresholds, depending on the base element, that must be exceeded to obtain acceptable oxidation behavior. Full article

Egg white was chosen as a renewable, non-toxic agent for the synthesis of FeMn₂O₄ spinel pre-catalysts to avoid the use of critical transition metals such as Ni and Co. However, synthesizing phase-pure FeMn₂O₄ remains challenging due to (i) the requirement of low oxygen partial pressures to counter rapid reoxidation of Mn₃O₄ in the presence of iron oxides, which can be achieved by the preferred oxidation of the egg white during the calcination, and (ii) the probable formation of Fe₃O₄ and Mn₃O₄ during intermediate steps in the reaction, leading to multiphase spinel formation caused by a miscibility gap between the spinels. In contrast, spinels with Ni, Co, Zn, or Al are phase-pure. Egg white has significant environmental impacts in the synthesis of all spinel manganites, as assessed from a life-cycle perspective, which can exceed those of petroleum-based agents such as ethylenediaminetetraacetic acid (EDTA) in most impact categories. Therefore, our results show that the investigated synthesis route is not more sustainable, and we demonstrate that implementing quantitative evaluation of environmental impacts already at an early stage is essential to determine whether a synthesis is truly sustainable. Full article

High-entropy oxides (HEOs) have garnered significant interest as next-generation anode materials for lithium-ion batteries (LIBs) due to their high theoretical specific capacity and excellent structural stability. This study successfully synthesized spinel-structured (Al_0.2Mn_0.2Co_0.2Ni_0.2Zn_0.2)₃O₄ HEO via a sol–gel method. The material was characterized by XRD, Raman and TEM, confirming a homogeneous single-phase spinel structure, with uniformly distributed elements-a hallmark of HEOs. Electrochemical tests demonstrated a stable cycling performance (438 mAh g⁻¹ at 100 mA g⁻¹ after 100 cycles and 350 mAh g⁻¹ at 1 A g⁻¹ after 1000 cycles) and rate capacity of 159 mAh g⁻¹ at 2 A g⁻¹, The remarkable long-term cyclability and good rate capability highlight the potential of this HEO for practical applications in durable, high-power lithium-ion batteries. This work underscores the advantage of incorporating structurally stabilizing elements in HEOs for advanced energy storage. Full article

Selective oxidation of benzyl alcohol to benzaldehyde is crucial for sustainable chemical synthesis, which provides the atom-economical and environmentally benign pathways. In this work, we used the in situ reduction immobilization to synthesize a series of Au nanoparticles supported by CoAlO_x support with spinel structure for alkali-free oxidation of benzyl alcohol. The synthesis methodology was preliminarily optimized and the influence of Co/Al molar ratio in Au/CoAlO_x on the catalytic performances was subsequently revealed based on characterizations. Results suggested that the electronic interaction between Au and CoAlO_x can be regulated and maximized under the Co/Al ratio of 3. It became a main factor to modulate the dispersion of Au nanoparticles, surface chemical composition, as well as the oxygen adsorption/activation ability. Benefiting from such synergistic interaction, the optimized Au/Co₃AlO_x catalyst achieved 86.1% BnOH conversion under 99.9% benzaldehyde selectivity with well-maintained structural stability under recycle tests. This work provides a rational design strategy for developing highly efficient gold catalysts with well-constructed Au-support interfaces for the alkali-free oxidation of alcohol. Full article

This study explores the catalytic performance of V³⁺-modified Mg/Al hydrotalcite-derived materials in the oxidative dehydrogenation (ODH) of n-butane, compared with catalysts derived from pyrovanadate and decavanadate precursors. Different methods for preparing hydrotalcite-like materials were applied to obtain vanadium-containing Mg-Al mixed oxide catalysts for n-butane ODH. The hydrotalcite-like precursors were doped with vanadates (V⁵⁺) via ion exchange or co-precipitation or with V³⁺ cations incorporated into brucite-like layers. During calcination in air or argon flow, different vanadium-containing phases were obtained. Our findings demonstrate that V³⁺-doped hydrotalcites exhibit superior activity and selectivity toward the total C₄H₈ products, with enhanced selectivity for 1,3-butadiene. The highest n-butane conversion was observed for catalysts with an MgO structure and vanadium dispersed in the oxide matrix. A similar conversion level (~44%) was obtained for a spinel-like Mg₂VO₄ catalyst, but only a 15% level was found for the highly crystalline α-Mg₂V₂O₇ catalyst. In contrast, the highest selectivities toward dehydrogenated products were observed for V³⁺-containing and α-Mg₂V₂O₇ catalysts. NH₃- and CO₂-temperature programmed desorption (TPD) analyses showed that high basicity combined with low acidity favors the formation of butene isomers and 1,3-butadiene. This work highlights the strategic potential of tailoring vanadium speciation and hydrotalcite-based catalyst design for low-carbon chemical manufacturing, supporting the transition toward a circular economy. Full article

Ferrospheres (FSs) are a microspherical component of fly ash from pulverized coal combustion. The wide variations in chemical and phase composition, morphology, and the spherical design of FSs suggest their use as functional materials capable of replacing expensive synthesized materials. A general understanding of the formation of FSs from thermochemical transformations of the mineral components of the original coal is important for identifying the most promising sources of FSs with a high content of a certain morphological type active in a specific process. A systematic SEM-EDS study of the composition–structure relationship of the skeletal-dendritic FSs isolated from fly ash has revealed common routes of their formation. These FSs are formed as a result of thermochemical transformations of iron-containing minerals with the participation of aluminosilicates of the original coals. The aluminosilicate precursor that determines the skeletal-dendritic structure is illite. The crystallization of skeletal-dendritic globules occurs due to the “seed” of Al, Mg-ferrospinel formed from the thermochemical transformation of illite. The general trend of change in the structure of globules from a coarse skeletal to a fine dendritic structure is associated with a decrease in the main spinel-forming oxides content and an increase in the silicate melt viscosity. Full article

Multilayer ceramic lithium batteries (MLCBs) are regarded as a new type of oxide-based all-solid-state microbattery for integrated circuits and various wearable devices. The chemical compatibility between the solid electrolyte and electrode active materials during the high-temperature co-sintering process is crucial for determining the structural stability and cycling performance of MLCBs. This study focuses on the typical MLCB composite electrodes composed of the NASICON-type Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) solid electrolyte and the spinel-type Li₄Ti₅O₁₂ (LTO) anode material. The thermal behavior, phase structure, morphological evolution, and elemental chemical states of these composite electrodes were systematically investigated over a co-sintering temperature range of 400–900 °C. The results indicate that the reactivity between LATP and LTO during co-sintering is primarily driven by the diffusion of Li from the LTO anode, leading to the formation of TiO₂, Li₃PO₄, and LiTiOPO₄. Furthermore, the co-sintered LATP-LTO multilayer composites reveal that the generation of Li₃PO₄ at the LATP/LTO interface facilitates their co-sintering integration at 800–900 °C, which is essential for the successful fabrication of MLCBs. These findings provide direct evidence and valuable references for the structural and performance optimization of MLCBs in the future. Full article

The purpose of this work was to consider the decolorization efficiency of reactive yellow 160 (Ry-160) dye utilizing cobalt aluminum oxide (AlCo₂O₄)-anchored Multi-Walled Carbon Nanotubes (AlCo₂O₄/MWCNTs) nanocomposites as catalysts for the first time in a photocatalytic process under natural sunlight irradiation. The compositional, morphological, and functional group analyses of AlCo₂O₄ and AlCo₂O₄/MWCNTs were performed by utilizing Energy Dispersive Spectroscopy (EDS), Field Emission Scanning Electron Microscopy (FE-SEM), and Fourier Transform Infrared (FTIR) Spectroscopy, respectively. A UV-Vis (UV-Vis) spectrophotometer was used to investigate degradation efficiency. The results exhibited a reduction in the optical bandgap for AlCo₂O₄/MWCNTs nanocomposites as catalysts from 1.5 to 1.3 eV compared with pure spinel AlCo₂O₄ nanocomposites. AlCo₂O₄/MWCNTs nanocomposites showed excellent photocatalytic behavior, and around 96% degradation of Ry-160 dye was observed in just 20 min under natural sunlight, showing first-order kinetics with rate constant of 0.151 min⁻¹. The results exhibited outstanding stability and reusability for AlCo₂O₄/MWCNTs by maintaining more than 90% photocatalytic efficiency even after seven successive operational cycles. The betterment of the photocatalytic behavior of AlCo₂O₄/MWCNTs nanocomposites as compared to AlCo₂O₄ nanocomposites owes to the first-rate storage capacity of electrons in MWCNTs, due to which the catalyst became an excellent electron acceptor. Furthermore, the permeable structure of MWCNTs results in a greater surface area leading to the onset of more active sites, and, in turn, it also boosts conductivity and reduces the formation of agglomerates on the surface of catalysts, which inhibits e−/h⁺ pair recombination. Concisely, the synthesis of a novel AlCo₂O₄/MWCNTs catalyst with excellent and fast photocatalytic activity was the aim of this study. Full article

Corrosion of the molten salts Na₂SO₄ and NaCl has become one of the major factors in the failure of steel components in boilers and engines. In this study, CoNiCrAlY cobalt-based cladding layers with different NiCr-Cr₃C₂ ratios were prepared by microbeam plasma cladding technology. The influence of the NiCr-Cr₃C₂ content on the microstructure, mechanical properties, and molten salt corrosion resistance of CoNiCrAlY was investigated. The CoNiCrAlY with a 25 wt.% NiCr-Cr₃C₂ (NC25) cladding layer possessed the highest microhardness (348.2 HV_0.3) and the smallest coefficient of friction (0.4751), exhibiting great overall mechanical properties. The generation of protective oxides Cr₂O₃, Al₂O₃, and spinel phase (Ni,Co)Cr₂O₄ is promoted by the addition of 25 wt.% NiCr-Cr₃C₂, which significantly reduces the corrosion of the cladding layer, and this effect is much more obvious at 950 °C than that at 750 °C. Furthermore, its corrosion mechanism was clarified. From the findings emerge a viable solution for the design and development of new high-temperature corrosion-resistant coatings. Full article

The high-temperature oxidation behaviour and phase stability of equi-atomic high entropy AlCrCoFeNi alloy (HEA) were studied using in situ high-temperature X-ray diffraction (HTXRD) combined with ThermoCalc thermodynamic calculation. HTXRD analyses reveal the formation of B2, BCC, Sigma and FCC, phases at different temperatures, with significant phase transitions observed at intermediate temperatures from 600 °C–100 °C. ThermoCalc predicted phase diagram closely matched with in situ HTXRD findings highlighting minor differences in phase transformation temperature. ThermoCalc predictions of oxides provide insights into the formation of stable oxide phases, predominantly spinel-type oxides, at high p(O₂), while a lower volume of halite was predicted, and minor increase observed with increasing temperature. The oxidation behaviour was strongly dependent on the environment, with the vacuum condition favouring the formation of a thin, Al₂O₃ protective layer, while in atmospheric conditions a thick, double-layered oxide scale of Al₂O₃ and Cr₂O₃ formed. The formation of oxide scale was determined by selective oxidation of Al and Cr, as further confirmed by EDX analysis. The formation of thick oxide in air environment resulted in a thick layer of Al-depleted FFC phase. This comprehensive study explains the high-temperature phase stability and time–temperature-dependent oxidation mechanisms of AlCrCoFeNi HEA. The interplay between surface phase transformation beneath oxide scale and oxides is also detailed herein, contributing to further development and optimisation of HEA for high temperature applications. Full article

The failure mechanism of a thermal barrier coatings (TBCs) system is investigated using cyclic thermo-mechanical loading with a thermal gradient. Hollow circular cylindrical specimens are employed, consisting of a nickel-based single-crystal alloy DD6 coated with a NiCoCrAlYHf bond coat via arc-ion plating and a surface electron beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia topcoat. The experimental setup allows for a surface temperature of 1130 °C and a substrate temperature of 1070 °C, while a tensile mechanical load of 200 MPa is employed to simulate the centrifugal stress in the middle of the high-pressure turbine blade. The comparison between TBCs with and without mechanical loading implies that the coupled thermo-mechanical load significantly promotes coating spallation since the superposition of mechanical strain enhances the local tensile stress at the peak region of the topcoat/thermally grown oxides (TGOs) interface. A subsequent interfacial morphology analysis demonstrates that the topcoat/TGO interface exhibited a degradation in the direction parallel to the mechanical loading axis. For all the specimens, TGO comprises a duplex structure, consisting of outer spinel and inner α-Al₂O₃. Full article

Low-carbon powertrains and sustainable fuels are closely linked as they both aim to reduce carbon emissions and transition away from reliance on fossil fuels. The methane from biogas, biomass, and organic waste can serve as an alternative energy source to traditional fossil fuels. The process of obtaining sustainable fuel (e.g., hydrogen and syngas) from methane is commonly confronted with the problems of carbon deposition on metal oxide. The study of carbon deposition characteristics during methane thermal conversion processes is particularly crucial for low-carbon powertrains. Herein, the carbon deposition on CoAl₂O₄ and strongly alkali-etched CoAl₂O₄ (CoAl^vO₄) spinel oxides from the CH₄ stage was investigated. We demonstrate that reaction time, calcination temperature, and reaction temperature have no effect on the compositions of carbon deposition, and the material itself plays a crucial role in carbon deposition. The graphitization degree for CoAl^vO₄ is lower than that for CoAl₂O₄. The strong alkali etching in CoAl₂O₄ only affects contents in different composition carbon deposition. This is mainly attributed to the introduction of Al³⁺ vacancies by alkali etching, which efficiently tunes the surface electronic structure in CoAl₂O₄. These findings guide designing efficient and clean low-carbon powertrains, especially in the development of removal carbon deposition technologies and catalysts. Full article

High-entropy alloys (HEAs) have attracted a great deal of research interest these days because of their attractive properties. Low-temperature chemical synthesis methods are being developed to obtain nanoscale HEAs with low energy consumption. In this study, we prepared HEA Al_0.2Co_1.5CrFeNi_1.5Ti_0.5 nanoparticles from high-entropy oxide (HEO) (Al_0.2Co_1.5CrFeNi_1.5Ti_0.5)₃O₄ by a deoxidation process via a CaH₂-assisted molten salt method at 600 °C. X-ray diffraction measurements demonstrated that the oxide precursor and the reduced product have single-phases of spinel structure and face-centered cubic structures, indicating the formation of HEO and HEA, respectively. The HEA nanoparticles exhibited superior catalytic performance in the liquid-phase hydrogenation of p-nitrophenol at room temperature with little leaching of the component elements. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX) exhibited a good distribution of constituent elements over the HEA nanoparticles in a micro-sized range. However, transmission electron microscopy (TEM) with EDX revealed a slight deviation of elemental distributions of Al and Ti from those of Co, Cr, Fe, and Ni in a nano-sized range, probably due to the incomplete reduction of aluminum and titanium oxides. The elemental homogeneity in the HEA nanoparticles could be improved by taking advantage of the HEO precursor with homogeneous elemental distributions, but the experimental results suggested the importance of the total reduction of oxide precursors to prepare homogeneous HEAs from HEOs. Full article