All‐solid‐state batteries with an alkali metal anode have the potential to achieve high energy density. However, the onset of dendrite formation limits the maximum plating current density across the ...solid electrolyte and prevents fast charging. It is shown that the maximum plating current density is related to the interfacial resistance between the solid electrolyte and the metal anode. Due to their high ionic conductivity, low electronic conductivity, and stability against sodium metal, Na‐β″‐alumina ceramics are excellent candidates as electrolytes for room‐temperature all‐solid‐state batteries. Here, it is demonstrated that a heat treatment of Na‐β″‐alumina ceramics in argon atmosphere enables an interfacial resistance <10 Ω cm2 and current densities up to 12 mA cm−2 at room temperature. The current density obtained for Na‐β″‐alumina is ten times higher than that measured on a garnet‐type Li7La3Zr2O12 electrolyte under equivalent conditions. X‐ray photoelectron spectroscopy shows that eliminating hydroxyl groups and carbon contaminations at the interface between Na‐β″‐alumina and sodium metal is key to reach such values. By comparing the temperature‐dependent stripping/plating behavior of Na‐β″‐alumina and Li7La3Zr2O12, the role of the alkali metal in governing interface kinetics is discussed. This study provides new insights into dendrite formation and paves the way for fast‐charging all‐solid‐state batteries.
Dendrite formation is a major challenge for all‐solid‐state batteries employing alkali‐metal anodes. Low interfacial resistance between sodium metal and ceramic Na‐β″‐alumina electrolytes is obtained by a surface heat treatment. This enables fast charging up to 12 mA cm−2.
In this article, the mechanism of sintering of Al2O3 in the presence of small amounts of Na2O and CaO was investigated. Based on the results of the electron microscopy, the granulometry and ...morphological features of the particles of the studied alumina were established. The uniform nature of the distribution of sodium-containing phases was revealed, in contrast to silicon-containing ones, and the dislocation of submicron particles from calcium-containing phases was determined mainly on the basal planes of relatively large corundum particles. It was shown that such an arrangement of calcium-containing phases promotes the formation of a dense layered microstructure during sintering, especially in the presence of -alumina. The general pattern of the branched mechanism of the reaction phase formation during the sintering of the compositions in the Na2O–СаО–Al2O3 system was illustrated by a diagram explaining the trend of physicochemical processes and the feasibility of using specific types of dispersed alumina for technologies of corundum products and refractory concretes with different contents of aluminous cements.
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•Phenol HDO was compared on Pd catalysts supported on alumina, zeolite HY and mixtures.•The 20%HY–80%Al2O3 support is beneficial for phenol HDO reaction over Pd catalyst.•The density ...of active phases on the support surface influenced on the HDO activity.•Catalyst acidity influence on both activity and coke formation.
This contribution describes the effect of the support (zeolite ultrastable HY, alumina (Al) and mixed HY–Al carriers) on the catalytic activity of Pd catalysts in the phenol hydrodeoxygenation (HDO) reaction carried out in a flow fixed-bed reactor at T=523–573–623K, P=15bar and WHSV=0.5h−1. Phenol dissolved in n-octane was used as model compound of bio-oil species derived from fast pyrolysis of lignocellulosic biomass. The catalysts were characterized by N2 physisorption, XRD, TPR, TPD-NH3, DRIFT spectroscopy of adsorbed CO, HRTEM, X-ray photoelectron spectroscopy (XPS) and TPO/TGA techniques. The largest phenol conversion (63%) achieved at 523K over the reduced Pd/20%HY–Al catalyst was similar to that obtained on a commercial NiMo/Al2O3–zeolite hydrocracking sample (HCK) activated by sulfidation. Regardless of the reaction temperature, the only products detected in the HDO of phenol over all catalysts studied were four O-free compounds: benzene, cyclohexene, cyclohexane, and methylcylopentene. Both reduced Pd/20%HY–Al and sulfided commercial HCK catalysts produced similar yields of O-free products. From the catalyst activity-structure correlation, it can be concluded that the HDO of phenol is favoured on the bifunctional Pd/20%HY–Al catalyst which possesses moderate acidity and improved Pd dispersion on the support surface. The contributions of the acid sites to the catalyst activity and deactivation by coke are discussed.
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•CNTs as a cosupport with alumina is loaded with MoNi.•The catalyst showed significant improvement in HDS of DBT.•While alumina provides good mechanical properties, CNTs enhance the ...dispersion and acidity.•Direct desulfurization mechanism was proposed to be predominant.
Alumina-carbon nanotubes (AlCNTs) were prepared as a support and loaded with MoNi catalyst (AlCNTMoNi). The same catalyst without the carbon nanotubes (CNTs) was also prepared to investigate their role. Techniques including N2 physisorption analysis, temperature programmed analysis, X-ray diffraction and scanning electron microscopy were used for characterization. The BET surface areas of the AlMoNi and AlCNTMoNi were 165 and 214 m2/g, respectively, while the total acidity was 0.36 and 1.53 mmol/g, respectively. The catalysts were investigated for their performance in the hydrodesulfurization (HDS) of dibenzothiophene in fuels in a batch reactor. The fuel used consisted of decalin with 550 ppm S. DBT conversions of 99% and 87% were achieved using the AlCNTMoNi and AlMoNi catalysts, respectively. The AlCNTMoNi catalyst also showed better performance than the control samples without CNTs, and physically mixed AlMoNi and AlCNTMoNi were used for comparison. The results indicate that adding CNTs into the γ-Al2O3 support enhanced the catalytic activity towards HDS due to its textural properties and surface morphology. Interestingly, the AlCNTMoNi catalyst showed excellent stability for up to five cycles, which indicates its suitability for industrial applications.
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•The mechanism of methyl-cyclohexane dehydrogenation is decoded on Pt13/Al2O3.•The Pt13 cluster’s reconstruction challenges the structure-sensitivity concept.•Several CH bond ...dissociation steps exhibit competing activation energies.•Dispersion corrections impact the free energy profile and BEP relationships.•The support influences the stability of some reaction intermediates.
By using density functional theory (DFT) and ab initio molecular dynamics, we investigate the dehydrogenation reactivity of 13 atoms platinum cluster supported on the γ-alumina (1 0 0) surface. We provide a detailed free energy profile and structural analysis of the dehydrogenation mechanisms of methyl-cyclohexane (MCH) into toluene. We highlight the quantitative impact of dispersion corrections on the free energy profile and on the adsorption configurations of the intermediates exhibiting a dual interaction with the cluster and with the alumina surface. During the step by step dehydrogenation of MCH, several reconstructions of the Pt cluster and hydrogen migrations occur. Due to the cluster ductility, they are moderately activated and provide optimal active sites catalyzing the CH bond cleavages. According to a preliminary kinetic analysis based either on energetic spans or on activation free energies of elementary steps, we found that many states and/or steps may be considered as determining ones. This may explain some diverging interpretations brought by previous experimental kinetic studies. We finally discuss how the cluster ductility challenges the historical concept of structure sensitivity/insensitivity for a given reaction in the case of nanometer-size metallic clusters dispersed on a support.
Alumina based rare earth oxides ceramic materials, with the good performance against the CMAS corrosion, were widely used as the thermal/environmental barrier coatings. In this work, three Y2O3–Al2O3 ...binary ceramic bulks, which were the Y3Al5O12, YAlO3 and Y4Al2O9, were prepared by high temperature solid state reaction using the Y2O3 and Al2O3 as the raw materials. The resistances to CMAS corrosion of these materials at 1250 °C and 1350 °C were compared fully. The compositions and structures of the samples before and after corrosion were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that the different chemical compositions of the materials resulted in the different optical basicity (OB) values which can decide the reactivity of the material with the CMAS melts. The Y3Al5O12 ceramic material was inert to the CMAS for its low OB value of 0.75 and damaged seriously by the CMAS through physical penetration. The YAlO3 and Y4Al2O9 with the high OB values of 0.80 and 0.87 reacted with the CMAS to form the Ca4Y6(SiO4)6O. The YAlO3 ceramic bulk exhibited the good performance against the CMAS corrosion benefitting from the formation of the Ca4Y6(SiO4)6O and the CaAl2Si2O8.
Advanced components in next-generation concentrating solar power (CSP) applications will require advanced heat-transfer fluids and thermal-storage materials that work from about 550°C to at least ...720°C, for integration with advanced power-conversion systems. To reach the cost target, less-expensive salts such as molten chlorides have been identified as high-temperature fluid candidates. High-strength alloys need to be identified and their mechanical and chemical degradation must be minimized to be used in CSP applications. Approaches for corrosion mitigation need to be investigated and optimized to drive down corrosion rates to acceptable levels—in the order of tens of micrometers per year—for achieving a long system lifetime of at least 30 years. Surface passivation is a good corrosion mitigation approach because the alloy could then be exposed to both the liquid and the vapor phases of the salt mixture. In this investigation, we pre-oxidized the alumina-forming alloys Inconel 702, Haynes 224, and Kanthal APMT at different temperatures, dwelling times, and atmospheres to produce the passivation by forming protective oxides at the surface. The pretreated alloys were later corroded in molten MgCl2 – 64.41wt% KCl at 700°C in a flowing Ar atmosphere. We performed electrochemical techniques such as open-circuit potential followed by a potentiodynamic polarization sweep and conventional long-term weight-change tests to down-select the best-performing alloy and pre-oxidation conditions. The best corrosion results were obtained for In702 pre-oxidized in zero air at 1050°C for 4h. Metallographic characterization of the pre-oxidized alloys and of the corroded surfaces showed that the formation of dense and uniform alumina scale during the pre-oxidation appears to protect the alloy from attack by molten chloride.
•Surface passivation was evaluated as a corrosion passivation approach.•Pre-oxidation was used to form protective oxides.•In702 (zero air, 1050°C, 4h) provided good corrosion resistance.•Dense/uniform alumina could be protecting the alloy from molten chloride attack.
•Two alumina-forming alloys, FeNiCrAl (ADSS) and FeCrAl (APM), were oxidized at 800, 900 and 1050 °C in steam.•ADSS showed slightly higher weight gain than APM above 900 °C due to the spinel oxide ...formation.•Two alumina-forming alloys showed highest weight gains at 900 °C.•Transient alumina caused the highest weight gain and alumina forming kinetics at 900 °C.
Two alumina-forming Fe-based alloys, duplex FeNiCrAl (alumina-forming duplex stainless steel, ADSS) and ferritic FeCrAl (APM) alloys, were oxidized in steam at 800 °C to 1050 °C for up to 72 h. Formation of spinel oxides on ADSS resulted in larger weight gain than APM, while the highest weight gain was observed at 900 °C. Outer γ- and/or θ-alumina and inner α-alumina were formed on APM, whereas dispersed spinel oxides as well as γ- and α-alumina on ADSS. Similar alumina formation kinetics was observed for both alloys, while transient alumina formation resulted in faster kinetics at 900 °C.
This study examined the influence of the crystallinity of added nano-alumina on the sulfate resistance of ordinary Portland cement (OPC) paste. Two crystalline types of nano-aluminas (α-and γ-phase) ...were incorporated in cement pastes, which were exposed to sulfate solution. In the results, both paste samples having α- and γ-phase aluminas had accelerated compressive strength loss and increased length expansion compared to the sample without alumina addition. In particular, the rapidly decreased dynamic elastic modulus of the nano-alumina added samples postulates the greatly increased internal stress likely by the increased formation of volume expansive reaction products, such as ettringite, which was supported by the XRD and TG results. The greater ettringite formation in the nano-alumina added samples was likely due to reactive AH
3
(=Al(OH)
3
) gel formation as the higher consumption degree of portlandite in the alumina added samples indirectly indicates the active AH
3
gel formation, resulting in additional ettringite formation from the reaction of AH
3
with Na
2
SO
4
solution. A further degree of sulfate attack was observed in the γ-alumina added sample for the long-term Na
2
SO
4
exposure (180 days) mainly due to the greater degree of gypsum formation inducing more internal expansive stress compared to the α-alumina added sample.
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