Al Species Research Articles

Study on the hydrolysis characteristics of polymeric aluminum chloride forced by fine bubbles and its key factors affecting the efficiency and capacity of forcing hydrolysis

Enhanced coagulation is an important way to remove natural organic matter and reduce disinfection by-products in traditional water treatment processes, in which the micromolecular organic matter that is difficult to be removed during conventional coagulation can be enhanced more conveniently by modulating the dominant Al species in the traditional metal salt coagulants (e.g., polymeric aluminum chloride, PACl). Based on the forcing hydrolysis characteristics of fine bubbles due to the adsorption of hydroxide ions on their surfaces, this study verified the adaptability of the forced PACl hydrolysis by fine bubbles under different operating conditions objectively and comprehensively. The morphological changes of PACl before and after forced hydrolysis by fine bubbles were characterized figuratively, and the evolution of the dominant Al species before and after forced hydrolysis by fine bubbles was reasonably elaborated. The experimental results showed that fine bubbles had the effect of forcing the hydrolysis of PACl with different degrees of alkalinity and modulating the dominant Al species. It was innovatively found that the mass transfer efficiency of the fine bubbles determined their efficiency in forcing PACl hydrolysis (Pearson's r = -0.9423) and the concentration of fine bubbles affected their capacity to force PACl hydrolysis (Pearson's r = 0.8189). At pH = 7 and an air flow rate of 20 mL/min, the DOC concentration of micromolecular organics and the DOC removal efficiency of total organics could be reduced by 0.54 mg/L and enhanced by 12.6 %, respectively, after forced PACl hydrolysis by fine bubbles. While deepening the mechanism of forced PACl hydrolysis by fine bubbles, the above results preliminarily verified the relevance and feasibility of modulating the dominant Al species through forced PACl hydrolysis by fine bubbles to improve the coagulation efficiency, which provided theoretical and data support for the construction of a fine bubble-enhanced coagulation process for drinking water treatment plants.

Comparative Study of Si−O−Al and Si−O−Si Bond Stability in HZSM‐5 Zeolite Under Steam and Hot Liquid Water Environments

AbstractUnderstanding the changes in the zeolite framework and catalytic active sites during zeolite‐based vapor‐phase and aqueous catalytic processes is crucial. Herein, the evolution of framework T atoms (Si and Al) in ammonium hexafluorosilicate (AHFS)‐treated HZSM‐5 zeolite under steam and hot liquid water (HLW) environments was inverstigated using various characterization techniques. In HLW, Si−O−Si bonds exhibit poorer hydrothermal stability than Si−O−Al bonds, in contrast to steam. Significant Si atom leaching occurs regardless of whether the framework tetrahedral Al atoms (Al(IV)‐1) are removed. Similar to steam, Al(IV)‐1 species in HLW sequentially evolve into partially coordinated framework Al species and then into extra‐framework Al (EFAL) species through partial and complete hydrolysis. The generated EFAL species act as Lewis acid sites, but their local structures or chemical environments may differ. These findings reveal the difference in the T−O−T bonds attacked by water molecules: the Si−O−Al bonds are primarily attacked in steam, whereas the Si−O−Si bond are primarily attacked in HLW.

Favorable formation of needle-shaped NiAl2O4 phase over macroporous Ni/CexZr1-xO2–Al2O3 catalysts in one-pot preparation and coke-resistant catalytic performance in dry reforming of methane

In this study, we report the formation of needle-shaped NiAl2O4 via favorable interactions between Ni and Al species over macroporous Ni/CexZr1-xO2–Al2O3 catalysts for dry reforming of methane (DRM) and its remarkable improvement in the catalytic performance. The macroporous catalysts prepared by a one-pot (OP) method promote a favorable interaction between Ni and Al species that results in the formation of unique needle-shaped NiAl2O4 due to easy access to each other compared with that by incipient wetness impregnation. The NiAl2O4 phase in the calcined catalysts transforms into highly dispersed Ni and defective Al2O3 via the Ni exsolution in the reduction step. The presence of oxygen vacancies near Ni0 species facilitates the CO2 activation and enhances the catalyst stability over DRM. The optimized distribution of active sites with abundant defects over macroporous Ni/CexZr1-xO2-Al2O3 catalysts (OP) result in high conversions of CH4 and CO2 and a low coking rate in DRM.

Unravelling the Crucial of Spatial Al Distribution to Realize Precise Alkali-Treatment for Target Acid-Catalyzed Reactions.

Constructing mesoporous structure within zeolites by alkali-treatment is an effective protocol to improve their diffusion properties. However, undesirable changes in Brönsted acid site (BAS) densities always offset this advantage in acid-catalyzed reactions. In this context, the crucial roles of spatial aluminumdistribution were unraveled during alkali-treatment of MFI zeolite and the desirable BAS density was achieved in obtained hierarchical samples for the target reactions. Various characterization methods, particularly the multiple one- and two-dimensional magic-angle-spinning (MAS) NMR techniques, were performed to track the alkali-treatment processes. For the sample with a more uniform spatial Al distribution, more tetrahedral Al sites would fall off and migrate around the Si-OH in zeolite as Al(OH)4-. Those re-deposited Al(OH)4- sites were easily transformed into NMR-invisible Al sites during the calcination process, which contributed negligibly to both Brönsted and Lewis acidities, thus being referred to"acid-free"Al species. While most tetrahedral Al sites were preserved after the alkali-treatment of sample with non-uniform Al distribution and the BAS density gradually increased with treatment time. According to the requirements of typical acid-catalyzed reactions, such as catalytic cracking of 1,3,5-triisopropylbenzene and methanol-to-olefins, the desired hierarchical zeolite catalysts were developed by matching the amounts of extracted Si and generated"acid-free"Al during the precise alkali-treatment.

Unravelling the Crucial of Spatial Al Distribution to Realize Precise Alkali‐Treatment for Target Acid‐Catalyzed Reactions

Constructing mesoporous structure within zeolites by alkali‐treatment is an effective protocol to improve their diffusion properties. However, undesirable changes in Brönsted acid site (BAS) densities always offset this advantage in acid‐catalyzed reactions. In this context, the crucial roles of spatial aluminum distribution were unraveled during alkali‐treatment of MFI zeolite and the desirable BAS density was achieved in obtained hierarchical samples for the target reactions. Various characterization methods, particularly the multiple one‐ and two‐dimensional magic‐angle‐spinning (MAS) NMR techniques, were performed to track the alkali‐treatment processes. For the sample with a more uniform spatial Al distribution, more tetrahedral Al sites would fall off and migrate around the Si‐OH in zeolite as Al(OH)4‐. Those re‐deposited Al(OH)4‐ sites were easily transformed into NMR‐invisible Al sites during the calcination process, which contributed negligibly to both Brönsted and Lewis acidities, thus being referred to“acid‐free”Al species. While most tetrahedral Al sites were preserved after the alkali‐treatment of sample with non‐uniform Al distribution and the BAS density gradually increased with treatment time. According to the requirements of typical acid‐catalyzed reactions, such as catalytic cracking of 1,3,5‐triisopropylbenzene and methanol‐to‐olefins, the desired hierarchical zeolite catalysts were developed by matching the amounts of extracted Si and generated“acid‐free”Al during the precise alkali‐treatment.

Impact of Hydroxy-Aluminum and Extracellular polymeric substances interactions on waste activated sludge Dewatering: A molecular perspective

Al13 and Al30 are the dominant aluminum (Al) species in polyaluminium chloride commonly used for sludge dewatering. However, the presence of extracellular polymeric substances (EPS) in the waste activated sludge hinders the coagulation effectiveness of Al-based coagulants. This study focused on the effects and mechanisms of Al13 and Al30 on treating sludge EPS. From a bulk perspective, the dosing of two coagulants significantly reduced the dissolved organic carbon and various organic compounds, reflecting their efficacy in removing organic substances in EPS. Further molecular characterization was revealed by FT-ICR MS. Al13 was more effective in removing lipids, lignins, and sulfur-containing compounds compared to Al30. Al13 also demonstrated a pronounced removal in components enriched in oxygen atoms (10–20) and KMD(COO) (0.5–0.7), suggesting its ability to remove molecules across a broader range of unsaturation. After coagulation with Al13, the areas corresponding to Al2p1/2 and Al2p2/3 in the Al2p spectra were more prominent compared to those in the Al30-coagulated EPS. Therefore, Al13 can both remove complex and low molecule weight compounds through abound forms of adsorption sites, making it more efficient in releasing bound water compared to Al30.

Revealing the Bro̷nsted Acidic Nature of Penta-Coordinated Aluminum Species in Dealuminated Zeolite Y with Solid-State NMR Spectroscopy.

The inevitable dealumination process of zeolite Y is closely related to ultrastabilization, enhanced Bro̷nsted acidity, and deactivation throughout its life cycle, producing complex aluminum and acidic hydroxyl species. Most investigations on dehydrated zeolites have focused on the Bro̷nsted acidity of tetra-coordinated Al (Al(IV)) and Lewis acidity associated with tricoordinated Al (Al(III)) sites, which has left the penta-coordinated Al (Al(V)) in dealuminated zeolites scarcely discussed. This is largely due to the oversimplified view of detectable Al(V) as an exclusively extra-framework species with Lewis acidity. Here we report the formation of Bro̷nsted acidic penta-coordinated Al species (Al(V)-BAS) in the dealumination process. Two-dimensional (2D) through-bond and multiquantum 1H-{27Al} correlation solid-state NMR experiments demonstrate the presence of a bridging Si-OH-Al(V) structure in dealuminated Y zeolites. Different from the conventional belief that water attack leads to the breaking of zeolite framework Al-O bonds in the initial stage of zeolite dealumination, the observed Al(V) as a dealumination intermediate is directly correlated with a BAS pair because of the direct dissociation of water on the framework tetrahedral aluminum (Al(IV)), thus bypassing the cleavage of Al-O bonds. 1H double-quantum solid-state NMR experiments and theoretical calculations provide further evidence for this mechanism, whereas pyridine adsorption experiments confirm stronger acidity of Al(V)-BASs than the traditional bridging hydroxyl groups associated with Al(IV). We were also able to detect the Al(V)-BAS site from dealuminated SSZ-13 zeolite with CHA topology, suggesting that its creation is not specific to the framework structure of zeolites.

Impacts of distinct residual aluminum on gypsum scaling in nanofiltration: Identification of key species

Membrane scaling severely hinders practical application of nanofiltration (NF) for brackish water treatment. However, the contributions of residual aluminum (Al), especially various species with differing polymerization degrees and sizes, to gypsum scaling remain unclear. Herein, the complex interactions between three Al species (AlCl3, Al13 and Al30) and gypsum scaling were investigated, including surface and bulk crystallization processes. Results demonstrated that Al species adhering to the membrane surface promoted surface crystallization and altered crystal morphology. Notably, the Al13 species induced the formation of dense, complete rosette crystals causing the most severe flux decline. For bulk crystallization, Al30 was the primary species to promote nucleation. This promotion resulted from two factors: a lower nucleation energy barrier and the promoted aggregation of small crystals. Furthermore, molecular dynamics (MD) simulations revealed that the inhibition of nucleation due to the competition between Al species and calcium ions at nucleation sites was negligible compared to the strong promotion effect. These findings demonstrated that PACl exhibit higher scaling potential during NF than monomeric Al coagulants. Ultimately, the competition between surface and bulk crystallization determined the final membrane flux decline. This study offers valuable insights into the mechanisms of NF scaling caused by residual Al and guides mitigation strategies.

Hierarchical EMT structured zeolites as improved catalysts for glycerol dehydration

A fast and simple post-synthesis method for creating secondary mesoporosity in EMT zeolites was developed using an ammonium fluoride / cetyltrimethylammonium bromide (NH4F/CTAB) solution at low temperature with ultrasound irradiation. This strategy is shown to be highly effective for producing hierarchical EMT structured zeolites through the etching of both Si and Al species. The catalytic performance of these materials were assessed using glycerol dehydration as a reaction test, which is in addition a relevant reaction due to the high amounts of glycerol generated as a by-product of biodiesel production. The resulting hierarchical EMT structured zeolites exhibited improved catalytic activity and high selectivity towards acrolein (around 80 %). This innovative approach creates new opportunities for using hierarchical EMT structured zeolites in processes related with biodiesel manufacture.

Atomic Layer Deposition of γ‐Al2O3 on Hexagonal Boron Nitride: A Hybrid Support for Metallocene Catalysts

AbstractHexagonal boron nitride (hBN), also known as white graphene, has recently gained larger attention due to its unique physical and chemical properties. Owing to its excellent thermal conductivity and stability, hBN has been reported as an effective filler in many polymers. This study explores the potential of hBN as a catalyst support and filler for olefin polymerization. We report the atomic layer deposition (ALD) of γ‐Al2O3 on hydroxyl‐functionalized hBN. The alumina precursor, methylaluminoxane, showed high selectivity, depositing Al species only on the B‐OH sites, while B−O‐O−B sites remained unreacted. The hBN/γ‐Al2O3 hybrid was characterized by Fourier transform infrared (FTIR) spectroscopy, X‐Ray diffraction and transmission electron microscopy (TEM). The deposition of the aluminum over the hBN sheets was confirmed. The hBN/γ‐Al2O3 was used as a support for metallocene catalysts. The supported catalyst complex was highly active and produced ethylene‐propylene polymers with molecular weights up to 10 times higher, as demonstrated by gel permeation chromatography (GPC)

Transformations to the aluminum coordination environment and network polymerization in amorphous aluminosilicates under pressure.

The structure of calcium aluminosilicate glasses (CaO)x(Al2O3)y(SiO2)1-x-y with the near tectosilicate compositions x ≃ 0.19 and 1 - x - y ≃ 0.61 or x ≃ 0.26 and 1 - x - y ≃ 0.49 was investigated by in situ high-pressure neutron diffraction and 27Al nuclear magnetic resonance (NMR) spectroscopy. The results show three distinct pressure regimes for the transformation of the aluminum coordination environment from tetrahedral to octahedral, which map onto the deformations observed in the production of permanently densified materials. The oxygen packing fraction serves as a marker for signaling a change to the coordination number of the network forming motifs. For a wide variety of permanently densified aluminosilicates, the aluminum speciation shares a common dependence on the reduced density ρ' = ρ/ρ0, where ρ is the density and ρ0 is its value for the uncompressed material. The observed increase in the Al-O coordination number with ρ' originates primarily from the formation of six-coordinated aluminum Al(VI) species, the fraction of which increases rapidly beyond a threshold ρthr'∼ 1.1. The findings are combined to produce a self-consistent model for pressure-induced structural change. Provided the glass network is depolymerized, one-coordinated non-bridging oxygen atoms are consumed to produce two-coordinated bridging oxygen atoms, thus increasing the network connectivity in accordance with the results from 17O NMR experiments. Otherwise, three-coordinated oxygen atoms or triclusters appear, and their fraction is quantified by reference to the mean coordination number of the silicon plus aluminum species. The impact of treating Al(VI) as a network modifier is discussed.

Alumanyl Reduction, Reductive Coupling and C-H Isomerization of Organic Nitriles.

The behavior of the potassium alumanyl, [{SiNDipp}AlK]2 ({SiNDipp} = {CH2SiMe2N(Dipp)}2; Dipp = 2,6-i-Pr2C6H3), toward organic nitriles has been investigated. In common with earlier studies of the reactivity of charge neutral Al(I) species with multiply bonded small molecules, it is suggested that the initial step in all the reactions involves [2 + 1] cycloaddition and the generation of an [η2-C=N-Al] alumina azacyclopropane unit. In the cases of o- and m-tolyl-substituted aryl nitriles, this species is too kinetically labile to allow its isolation and undergoes C-C coupling via immediate Al-C/C≡N insertion to yield the alumina diazabutadiene derivatives. In contrast, the increased steric profile of alkyl nitriles imposes a marked influence on the nature of the products formed. Consistent with the proposed sequential pathway, reaction of [{SiNDipp}AlK]2 with t-BuCN provides an isolable alumina cyclopropane species that is kinetically resistant to onward reaction with a further nitrile equivalent. While reduction in the alkyl nitrile steric demands by use of i-PrCN again facilitates C-C bond formation, the crowding of the Al center by the resultant alumina-diazabutadienediide moiety appears to be beyond the limit of kinetic viability, resulting in an unusual 2-fold C-H to N-H isomerization from one of the C-iso-propyl substituents and the isolation of a 1-alumina-2,5-diazabutadiene structure.

Anodization of cast and sintered Fe40Al alloy in etidronic acid: Morphological and semiconductive properties of the oxide films

Fe40Al alloys produced by casting and sintering were anodized to form nanostructured oxide layers. Microstructural characterization revealed a lower grain size for the sintered alloy compared to the cast alloy. Anodizing was performed in four electrolytes with a constant etidronic acid concentration (0.3 M) and different ethylene glycol-water ratios. Different voltages (5–400 V) and treatment times (1–4 hours) were evaluated for cast and sintered Fe40Al alloys. Among the studied anodization regimes, only four anodic films formed on sintered Fe40Al were homogeneous. These films were annealed at 900°C and analyzed by conventional characterization techniques (SEM/EDS and XRD). Results indicated a non-self-ordered morphology and different content of P, Fe, and Al species as a function of the electrolyte composition. Annealing post-treatment led to the formation of Fe/Al oxides and spinels in selected anodic films. An additional peak of FePO4 was detected only in the anodic film formed in pure ethylene glycol. The band gap values (UV-Vis reflectance spectroscopy) of the anodic film formed in ethylene glycol decreased from 2.87 eV to 2.45 eV after annealing. This band gap decrease was associated with the preferential formation of conductive phases (Fe2O3 and FeAlO3) over insulating phases (γ-Al2O3 and FeAl2O4) after annealing.

Efficient and selective recovery of Mo and V from spent hydrodesulfurization catalysts via oxidation roasting followed by Na2CO3 and NaOH leaching

Spent hydrodesulfurization (HDS) catalysts containing large amounts of valuable metals, such as Mo and V, are hazardous solid wastes but also valuable secondary resources. However, the current recovery process suffers from the difficulty of balancing the leaching efficiency of Mo and V and their selectivity over Al. This work focused on the effect of phase transformation during roasting operation on the leaching behavior Mo, V, and Al and adopted an oxidation roasting followed by mixed alkali of Na2CO3 and NaOH leaching process to recover Mo and V from spent HDS catalysts. The results indicated that the phase transformation of Mo, V, and Al species during oxidation roasting process played a crucial role in achieving efficient leaching of Mo and V, as well as reducing leaching efficiency of Al. This transformation involved the change in Mo and V species changed from low valent compounds to high valent oxides, and Al2O3 from γ-phase to θ- and α-phases. In addition, efficient and selective leaching of 99.3% Mo and 97.8% V was realized, with only 0.03% Al being dissolved, by roasting the spent catalysts at 700 °C for 2 h and then leaching with a mixed solution of 1.2 mol/L Na2CO3 and 1.6 mol/L NaOH. The efficient and selective leaching of Mo and V can significantly reduce the burden of subsequent separation and purification, which provided an important prerequisite for the development of a new process for the recovery of Mo and V from HDS spent catalysts in alkaline systems.

Extended Cycle Life Pb-Ion Batteries with High Coulombic Efficiency Exceeding 99.96% from Al/Pb Bimetallic Eutectic Electrolyte

Following renewable energy development, batteries are the most crucial way to establish an energy storage system. In the past hundred years, lead-acid batteries have been widely applied in industrial and vehicle applications. Their low cost, simple manufacturing, and good safety can compete with lithium-ion batteries. However, some challenges still exist, e.g., poor low-temperature performance and short cycle life; aqueous solution is the reason that oxygen evolves from positive electrodes, resulting in positive active material detached from the electrode. Thus, developing novel lead-ion batteries to replace lead-acid batteries is a significant issue. In metal-ion batteries research, deep eutectic solvent (DES) has been well developed in recent years due to its high thermal stability and wide electrochemical window. Herein, a new Al/Pb bimetallic eutectic electrolyte (BEE) composed of aluminium perchlorate (Al(ClO4)3·9H2O), lead perchlorate (Pb(ClO4)2·3H2O), and succinonitrile (SN) with acetonitrile (ACN) as an additive, mixing in molar ratio. To realize the medium effect in this electrolyte, the BEE is compared with concentrated Pb(ClO4)2 aqueous solution. The ion conductivity, viscosity, and thermal stability depend on the metallic salt/SN ratio, and we proposed that the optimized molar ratio is 1:1:12:5. It exhibits outstanding thermal stability within − 50 to 50 °C. From Fourier-transform infrared spectroscopy (FTIR) spectrum analysis in BEE, the O-H stretching decreased, and the ClO4 - stretching band increased, compared to the concentrated Pb(ClO4)2 aqueous solution; it can be understood that O-H interaction between Pb2+ and ClO4 - is weakened; meanwhile, ClO4 - ions participated in first solvation shell. This variation reduces the desolvation energy of Pb2+ to facilitate smoother lead plating/stripping and enables better electrochemical performance. To validate the effect of the solvation structure variation, assembling the Pb/Pb symmetric cell and Pb/Platinum (Pt) asymmetric cell are essential methods. Pb/Pb cell maintains a stable voltage hysteresis of about 20 mV even cycling 2500 h at the current density of 0.5 mA cm-2, Pb/Pt cell under galvanostatic conditions successfully performs highly reversible Pb plating/stripping, achieved average coulombic efficiency (ACE) >99.96% in BEE for more than 1000 h at current density 0.5 mA cm-2. Furthermore, we utilize BEE in Na3V2(PO4)3(NVP) and natural graphite (NG) as cathode material; the reversible Pb2+ and ClO4 - (de-)intercalation are respectively observed in Pb/NVP and Pb/NG full cell, Pb/NVP cell exhibited long-term cycling stability with 80.95% capacity retention and 98.21% ACE after 600 cycles at a current density of 100 mA g-1, then Pb/NG cell remains high discharge voltage plateau (≈1.7V) with 72% capacity retention after 200 cycles at a current density of 100 mA g-1. Electrochemical impedance spectroscopy (EIS) of Pb/NVP in BEE-1:1:12:0 and 1:1:12:5 shows that adding the ACN additive can decrease the solution resistance (Rs) and charge transfer resistance (Rct) of the cell. Ex-situ X-ray photoelectron spectroscopy (XPS) was performed on the Pb surface at the charging state, observing that Al species are co-deposited, revealing the synergistic effect between Aluminium perchlorate and Lead perchlorate. From the ex-situ X-ray diffraction (XRD) patterns of cycled NVP and NG cathode at charge/discharge states, some irreversible variation of peak position occurred, indicating that ion (de-)intercalation after operation; these results demonstrate BEE performed bi-functional ion (Pb2+ and ClO4 -) intercalation phenomenon. To further confirm the Pb2+ dynamic in the NVP cathode at charge/discharge progress, the X-ray absorption spectroscopy (XAS) characterization was applied. The comparison of XANES spectra collected at the V K-edge, the XANES shift to lower energy during discharging, this exhibition is consistent with reduction reaction of V4+ to V3+, the EXAFS spectra show the local structure change of V-P/Na/Pb bonds. The EXAFS spectra at the Pb LIII-edge indicated that the Pb-O distance is shortened during discharging; the abovementioned results demonstrate the Pb2+ (de-)intercalation process in the NVP structure.In conclusion, this work proposed a novel bimetallic eutectic electrolyte for potential lead-ion batteries that enables stable Pb plating/stripping. The cycle-life and capacity retention of Pb/NVP and Pb/NG full-cell with BEE is significantly improved by adding acetonitrile (ACN) additive. The XAS characterization further confirmed the (de-)intercalation of Pb2+ in the NVP cathode. A stable, high-voltage, and high-capacity positive electrode is needed, allowing the reuse of secondary lead metal to be applied to next-generation energy storage. Figure 1

The Ether‐Adduct of a Lewis Superacidic, Dicoordinate Aluminum Hydride Cation and the Ion Affinities of Solvent‐Adducts

AbstractAluminum reagents are widely used as strong Lewis acids for organic transformations and catalysis. In recent years, a variety of Al‐Lewis superacids could be accessed by preparation of aluminum cations paired with weakly‐coordinating anions or by use of perfluorinated substituents at the metal. While the majority of these Al‐Lewis superacids is composed of a tricoordinate Al‐metal atom, examples for dicoordinate Al species are very scarce. In this study, we report the preparation of [(Mes*)Al(H)(OEt2)]+[Al(ORF)4]− (Mes*=2,4,6‐tBu3‐C6H2, RF=C(CF3)3) by reaction of protonated ether [H(OEt2)2]+[Al(ORF)4]− with [Mes*AlH2]2. Structural analysis supported by computed frontier orbitals and atomic charges reveals that the cation is best described as diethylether adduct of dicoordinate [(Mes*)Al(H)]+ and acts as synthon to this low‐coordinate cation. To incorporate the masking of the coordination site by the ether, the enthalpy of dissociation is included in the computed fluoride‐ and hydride ion affinities (XIA) and entropic effects are treated by defining a “free ion affinity” (fXIA), basing on the Gibbs energy change. Hereby, the Lewis acidity of free Lewis acids as well as their solvent adducts can be estimated.

Organosilane-assisted synthesis of EU-1 nanozeolite aggregates with improved activity in catalytic cracking of n-hexane

One-dimensional microporous zeolite, EU-1, exhibits more favorable selectivity of propylene in cracking of petroleum components. However, it faced the problem of low catalytic activity for the poor utilization of active sites. In this work, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC) was used to functionalize protozeolitic units and inhibit the excessive growth of crystals by the long hydrophobic alkyl chain. The introduction of TPOAC decreased the crystal sizes into nanoscale, enhanced the mesoporous volume of EU-1 zeolite, and exposed more external acid sites. Moreover, TPOAC could interact with Al species, and in this case, fewer Al atoms were incorporated into the zeolite framework, reducing the acid strength and amount. Intelligent gravitation analyzer test indicated that the zeolite prepared with the presence of 0.30 g TPOAC exhibited the largest accessible volumes in n-hexane adsorption, and the highest accessibility of acid sites, which synergistically promoted cracking of n-hexane for the production of light olefins.

Microstructural Modifications and Failure Mechanisms of an Aluminum‐Based Abradable Coating System during Isothermal and Cyclic Aging

Abradable systems are used in the aeronautical industry to improve the efficiency of gas turbine. Those materials are exposed in service to temperature up to 450 °C. The increase in gas turbine efficiency requires to increase the operating temperature and therefore the service temperature of abradable coating. The present study focuses on the isothermal and cyclic thermal aging of the Al–Si abradable coating system in a laboratory air at high temperature up to 500 °C. The investigation encompasses the microstructural evolution, phase transformation, and the formation of cracks, along with their interrelated effects. During aging, silicon particles precipitate in the abradable top coat. In addition, coarsening of those particles is observed and the coarsening kinetics appears to be faster in cyclic thermal aging conditions compared to isothermal aging. During cyclic and isothermal aging, brittle aluminides develope at the abradable top–coat/bond–coat interface, due to the interdiffusion of Al and Ni species. During cyclic aging, thermal cycles create thermomechanical stress at the top‐coat/bont‐coat interface due to coefficient of thermal expansion mismatch between the Al‐Si deposit and intermetallic phases. The stress generated results in the formation of cracks and porosities at the top–coat/bond–coat interface resulting in a dramatic failure of the system.

Uniform, Fully Connected, High-Quality Monocrystalline Freestanding Perovskite Oxide Films Fabricated from Recyclable Substrates.

Releasing epitaxial perovskite oxide films from their native oxide substrates produces high quality, 2D-material-like monocrystalline freestanding oxide membranes, as potential key components for the next-generation electronic devices. Two major obstacles still limit their practical applications: macroscopic material defects (mainly cracks) that lowers uniformity and yield, and the high cost of the consumed oxide substrates. Here, a two-step film transfer method and a substrate recycling method enable repetitive fabrication of millimeter-scale, fully-connected freestanding oxide films of various chemical compositions from the same substrates; arrays of capacitor and resistor devices based on these oxides transferred on silicon indicate high uniformity, low sample-to-sample variation, and satisfactory electrical connectivity. The two-step transfer suppresses crack formation by avoiding buckling-delamination-type relaxation of epitaxial strain, and the key point to achieve substrate reuse is to remove the residual Al species bonded to the substrate surfaces. The mitigation of such long-lasting issues in freestanding oxide fabrication techniques may eventually pave roads toward future industrial-grade devices, as well as enabling many research opportunities in fundamental physics.

Enhanced Co3O4 Nanoflakes Reactivity via Integrated Al-Doping and Metal Vacancy Engineering for Large Capacity Li-CO2 Batteries

Rechargeable Li-CO2 batteries are well-regarded for their high-energy, environmental friendliness, and resourceful use of CO2, but suffer from poor cycle reversibility. Herein, Al-doped Co3O4 nanoflakes featuring abundant metal vacancies (V-ACO/CC) were synthesized via a facile approach employing Al ions as both a dopant and sacrificial agents, which serve as high-efficient cathode catalyst for Li-CO2 batteries. Experiment results demonstrate that the incorporation of Al doping and metal vacancies modulates the electronic structure of Co-center and optimizes the growth path of discharge product. The cation vacancies generated by the sacrificed part of the Al atoms change the local charge distribution, strengthen the affinity of CO2 and reaction intermediates and facilitate the reversible decomposition of discharge products. Concurrently, the formation of covalent Al-O bonds by the remaining Al species reinforces the stability of nanostructures. Notably, the V-ACO/CC-based LCBs exhibit enhanced CO2 conversion kinetics, as evidenced by a high specific capacity (12.06 mAh cm−2 at 0.05 mA cm−2), fast rate capability and impressive stability (over 420 cycles under 0.1 mA cm−2).