Aluminum Coordination Research Articles

Impact of MgO-ZnO substitution on nucleation of aluminosilicate glasses

The nucleation mechanisms is of technically interest and important in glass-ceramics production. Here we investigate the nucleation behaviors of NiO-doped MgO-Al2O3-SiO2 and ZnO-Al2O3-SiO2 glasses. It is found that crystallization tends to takes place on the surface and the interior of glasses for the former and the latter, respectively. The origin of different nucleation behavior is studied by comparing aluminum coordination, configurational entropy and rheological properties of the glasses. The substitution of MgO by ZnO leads to increase of tetrahedral aluminum concentration, and decrease of configurational entropy above glass transition temperature, in particular, the latter is closely related to volume nucleation. In addition, the qualitative comparison of thermodynamic and kinetic barriers of steady-state nucleation rate of two glasses indicates that ZnO-bearing aluminosilicate glass possesses higher diffusivity and lower critical nucleus size, which favoring volume nucleation.

Unraveling the Structural Evolution of Aluminum Polyoxocations in Solution.

The primary objective within the realm of aluminum solution chemistry is to elucidate the structural changes in aluminum polyoxocations under the influence of altered solution conditions. Notably, previous reports are primarily focused on specific types, such as aluminum monomers, species from the Keggin series, and the planar Flat-Al1315+ (F-Al13) cluster. As a result, there is a lack of comprehensive understanding of the remaining aluminum polyoxocations and their respective transformation pathways. In response to this lack, we adopt a combined experimental and theoretical approach to explore the spectral properties of aluminum polyoxocations. Specifically, we analyze infrared spectra, Raman spectra, and aluminum-27 nuclear magnetic resonance (27Al NMR) spectra. Notably, the changes in the spectral features originate from varying solution basicity levels. Through our findings, we can categorize the Al-O clusters into three primary groups: Al(H2O)63+ (Al1), ε-Keggin-[AlO4Al12(OH)24(H2O)12]7+ (ε-Al13), and 6-coordinated aluminum species. Notably, the Raman spectra exhibit prominent peak shifts at 559 and 595 cm-1, indicating the existence of Al3(1) intermediates during the transition from the Al monomer to the ε-Al13 cluster. Overall, this paper presents a comprehensive summary of the possible mechanisms that govern the formation of ε-Al13 from Al3(1), offering a clearer picture of the aluminum polyoxocation landscape and its dynamics under various solution conditions.

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.

Temperature‐Induced Modifications in Natural Zeolite Clinoptilolite: Effects on Acidity and Catalytic Acetalization

AbstractThis study delves into the acid modification of natural zeolite clinoptilolite, focusing on the identification of acid site types and their catalytic activity in the Brønsted acid‐catalyzed acetalization of benzaldehyde with 1,3‐butanediol. Following calcination, the samples underwent acidification via ammonium‐ion exchange, resulting in approximately 45 % of the clinoptilolite cations being exchanged with ammonium ions. The investigation evaluates the structural, morphological, and textural alterations induced by this modification using XRD, FTIR, and nitrogen adsorption‐desorption measurements. Ammonia‐temperature‐programmed desorption (NH3‐TPD) analysis confirms the presence of medium to strong acidic protons, highlighting the acidity of the modified samples. Employing 27Al and 29Si magic‐angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy elucidated changes in the state and coordination of aluminum post‐sample activation. Specifically, the 27Al MAS NMR spectra indicate a partial dealumination, evidenced by the emergence of 5 and 6‐fold coordinated aluminum. Moreover, 29Si MAS NMR measurements tracked variations in the Si/Al ratio. The study probes the nature of these sites, their influence on catalytic activity, and the synergistic interplay between Brønsted acid sites and 5‐fold coordinated aluminum. The results showcase that the prepared acidic natural clinoptilolite catalysts augment acidity and porosity, fostering promising implications for catalytic applications.

Influence of high-pressure on the short-range structure of Ca or Na aluminoborosilicate glasses from 11B and 27Al solid-state NMR

The present study investigates the boron and aluminium speciation of aluminoborosilicate glasses synthesised under ambient to high-pressure conditions (up to 2.0 GPa) using 11B and 27Al Nuclear Magnetic Resonance. Four glass series were prepared in the SiO2-Al2O3-B2O3-Na2O/CaO system, with either high or low R' values (R'=([Na2O]+[CaO])/([B2O3]+[Al2O3])). 11B NMR reveals a linear increase in four-coordinated boron (BO4) with pressure for Ca glasses and non-linear with a plateau between 0.5 and 1.5 GPa for Na glasses. 27Al NMR reveals minimal pressure impact on aluminium coordination in sodium glasses. Conversely, calcium glasses form higher-coordinated AlO5 and AlO6 units under pressure. The determination of non-bridging oxygen (NBO) variation witnesses the change in compensation mechanism for boron species. In low R' glasses, limited NBOs suggest Na+/Ca2+ release from AlO4 as the primary compensation source. This work sheds light on pressure's influence on network connectivity in simple glasses, aiding the understanding of complex glass behaviour.

Controlled engineering of high-purity pseudo-boehmite with large pore volume by aluminum alkoxide hydrolysis: Mechanistic understanding and reforming catalysis

The mechanistic understanding of the pore formation during aluminum alkoxide hydrolysis is of crucial importance for the controlled engineering of large pore volume pseudo-boehmite. The time-dependent structure evolution during n-hexanol-aluminum hydrolysis and the DFT calculations were performed to monitor the changes in the aluminum coordination. The results show that the hydrolysis, oxolation and alcoxolation reactions dominate the pore construction in turn with the continuous addition of water. The aluminum coordination undergoes aggregation from Al tetra-coordinates to Al hexa-coordinates and further stable Al3hexa-coordinates as repeating units for linear growth. The rate and amount of water injection is critical for the retention of at least one OR (R = -C6H13) group, which acts as a directed pore-forming group to promote the large cyclization growth of the Al3hexa-coordinates. Consequently, 1.44 cm3/g pore volume of high-purity pseudo-boehmite was obtained, and the prepared PtSn-Al2O3 catalyst exhibits a > 80 % of toluene selectivity for n-heptane reforming.

Enhancing Hydride Transfer in Catalytic Hydrogenation via σ-Electron-Induced Polarization of Imines.

In this study, we investigated the role of aluminum cations in facilitating hydride transfer during the hydrogenation of imines within the context of Noyori-type metal-ligand cooperative catalysis. We propose a novel model involving aluminum cations directly coordinated with imines to induce activation from the lone pair electron site, a phenomenon termed σ-induced activation. The aluminum metal-hydride amidate complex ("HMn-NAl") exhibits a higher ability of hydride transfer in the hydrogenation of imines compared to its lithium counterpart ("HMn-NLi"). Density functional theory (DFT) calculations uncover that the aluminum cation efficiently polarizes unsaturated bonds through σ-electron-induced activation in the transition state of hydride transfer, thereby enhancing substrate electrophilicity more efficiently. Additionally, upon substrate coordination, aluminum's coordination saturation improves the hydride nucleophilicity of the HMn-NAl complex via the breakage of the Al-H coordination bond.

Shutters-Inspired metal ions coordination hydrogel Strain/Pressure sensor for joint behavior evaluation and flatfeet correction

The metal ions coordination hydrogels (MI-HG) that polymer gels serve as flexible substrates and metal ions as conductive media have emerged as flexible electronic sensor materials. Nevertheless, fabricating MI-HG by a traditional soaking method is difficult to guarantee the good permeation of metal ions, manifesting as the “core–shell” structure of MI-HG, which undoubtedly reduces their mechanical property, conductivity, and sensitivity. Inspired by the shutter opening and closing regulation mechanism, a strategy that completely opening the backbone layers of polymer gels facilitates metal ions permeation thus improving the whole performance of MI-HG, especially the mechanical property is proposed. Herein, poly(vinyl alcohol)(poly(acrylic acid)-polyacrylamide) (PVA(PAA-PAM)) is used as the typical polymer hydrogel (HG), trivalent aluminum ion (Al3+) as the metal salt, and N,N'-methylenebisacrylamide (MBAA) as the important regulation ‘rod’, fabricating a series of aluminum coordination hydrogels (Al-HGx%). The results indicate that the mechanical performances of Al-HG2% are significantly improved. For example, the toughness of Al-HG2% reaches 996.12 KJ/m3, approximately three times that of the Al-HG0% sample (354.45 KJ/m3). The combination of structural characterization as well as finite element analysis, the mechanism for the enhanced mechanical performances based on shutter’s completely open effect is elucidated, the product of which (Al-HG2%) has potential application in flexible strain/pressure sensor for joint behavior evaluation and flatfeet correction.

High selective, sensitive, reversible and imaging application sensor for Aluminium detection

Aluminium plays an important role in many areas, which has been shown to be associated with some serious diseases. According to the coordination of aluminium with N and O, we conducted probe Sal-cn for the detection of Al3+, the structure of Sal-cn was determined by HR-MS, NMR and IR. Sal-cn showed a good selective and sensitive response towards Al3+ via a fluorescence turn-on output. The detection limit was 0.21 μM. The mechanism was carried out by Job's plot, HR-MS and DFT and related to the coordination of aluminium. What's more, the reversibility showed that Sal-cn could be used for 3 times. Besides, Sal-cn was used for imaging of Al3+ in HEK293T cells.

Preparation of one-part geopolymers using coal gasification slag: Effect of alkali fusion product additive and liquid/solid ratio

In this work, one-part geopolymers were synthesized through the alkali fusion and component additive method (AFCAM), utilizing coal gasification slag as the primary raw material. The investigation delved into the influence of varying fusion product contents and liquid/solid (L/S) ratios on the geopolymer properties. The experimental results demonstrated a non-linear correlation between the increase in fusion product content and the compressive strength of geopolymers, revealing an initial ascent followed by a subsequent decline. Additionally, a lower L/S ratio of 0.3 was observed to enhance compressive strength compared to the L/S ratio of 0.4. Notably, the optimal combination of an L/S ratio of 0.3 and a fusion product percentage of 30 % resulted in a remarkable compressive strength of 25.2 MPa. The comprehensive strength analysis suggested that an adequate amount of fusion product enhances the geopolymerization reaction, evidenced by the transformation of aluminum coordination states. Specifically, the conversion of five-coordinated and six-coordinated aluminum in slag to four-coordinated aluminum in geopolymers was observed. Concurrently, increased silicon and aluminum reactivity led to the formation of a robust Q4(4Al) network in the geopolymer gel. The impact of L/S ratios was attributed to the accelerated dissolution and hydrolysis of aluminosilicates at an elevated L/S ratio of 0.4, hindering polycondensation. These outcomes underscore the pivotal role of fusion product content and L/S ratio in governing the strength development of one-part geopolymers.

The effect of iodine on the local environment of network‐forming elements in aluminoborosilicate glasses: An NMR study

AbstractKnowledge of the structural organization of nuclear waste glasses at the atomic scale is the basis for further studies of macroscopic properties (e.g., fracture toughness, chemical durability, and leaching rate). Recent studies have focused on the iodine dissolution mechanism in oxide‐based glasses synthesized under high‐pressure conditions, but there is still a lack of key information on the extent of the modifications caused by iodine entering the glass network. We therefore decided to conduct an in‐depth study by nuclear magnetic resonance on two series of aluminoborosilicate glasses synthetized under high pressure conditions and doped with either I2 or I2O5. The obtained 11B, 23Na, and 27Al nuclear magnetic resonance (NMR) spectra were fitted and correlated with the iodine content in order to find possible relationships with the local environment change for the probed cations. These data showed that iodine has no effect on the coordination of aluminum and very little effects on that of boron. In contrast, we found an expected relationship of the I content with the 23Na NMR parameters. In comparison with previous studies on the non‐bridging oxygen (NBO) distribution in aluminoborosilicate, we suggest that Na+ is mainly scavenged from silica tetrahedra with one or two NBO ( or ) as no boron planar triangles with one NBO are expected for such compositions. From those information, we establish a model for iodine dissolution in nuclear waste glass that is consistent with previous studies.

Al/SBA-15 Mesoporous Material: A Study of pH Influence over Aluminum Insertion into the Framework.

Herein, ordered mesoporous materials like SBA-15 and Al/SBA-15 were prepared using the pH adjustment method. Thus, these materials were developed in different pH of synthesis, from the pH adjustment method using a KCl/HCl solution and varying the Si/Al molar ratio (5, 25, and 75). All the ordered mesoporous materials were characterized by FRX, 27Al NMR, SEM, XRD, N2 adsorption/desorption, and CO2 adsorption. From the applied method, it was possible to obtain SBA-15 and Al/SBA-15 with high mesoscopic ordering based on the XRD patterns, independent of the pH employed. From the chemical composition, the insertion of higher amounts of Al into the synthesis caused a progressive improvement in the structural and textural properties of the ordered mesoporous materials. Thus, the chosen synthesis conditions can lead to different aluminum coordination (tetrahedral and octahedral), which gives these materials a greater potential to be applied. The presence of Al in high amounts provides material with the ability to form micropores. Finally, the proposed method proved to be innovative; low-cost; less aggressive to the environment, with efficient insertion of aluminum in the framework of SBA-15 mesoporous material; and practical, based on only one step.

Kinetic partitioning of trace cations between zoned clinopyroxene and a variably cooled-decompressed alkali basalt: Thermodynamic considerations on lattice strain and electrostatic energies of substitution

We present kinetic partitioning data for trace cations measured in zoned clinopyroxene crystals obtained from a variably cooled and decompressed olivine basalt erupted at Mt. Etna volcano in Italy. Supersaturation effects and compositional heterogeneities at the interface melt lead to the development of sector zoning, concentric zoning, and patchy zoning in clinopyroxene crystals. Apparent partition coefficients between compositionally different growth layers and adjacent melts (Di) for isovalent groups of trace elements are tested for internal consistency on the thermodynamic basis of lattice strain (ΔGstrain) and electrostatic (ΔGelec) energies of substitutions. The excess energy of partitioning (ΔGpartitioning) for trace cations in zoned crystals accounts for a kinetic incorporation control leading to large enthalpic effects through distortion of the lattice and changes in the electrostatic forces. ΔGpartitioning depends upon the complementary relationship between ΔGstrain and ΔGelec, which is the most appropriate thermodynamic description for the accommodation of rare earth elements and high field strength elements in the lattice site of zoned crystals. Polyhedral sectors, skeletal forms, and overgrowth zones have Di values settled by the number of charge-balanced and -imbalanced configurations taking place in the lattice site as a function of aluminium in tetrahedral coordination, and crystal structural changes produced by heterovalent cation substitutions. In an energetically unstable macroscopic system ruled by cooling and decompression, thermodynamic requirements for the crystallochemical control of Di encompass the attainment of local equilibrium at the crystal-melt interface via the establishment of small-volume reaction kinetics. The requisite of local interface equilibrium is however susceptible to the anisotropic growth velocity of each specific clinopyroxene surface, thereby giving reason to different energetic properties of the crystallographic site. This axiomatic control requires that transition metal cations partition also in consideration of electronic effects related to the crystal field stabilization energy. The overriding implication is that Di values for trace cations having different size, charge, and electronic configuration serve as sensitive probes of the different crystal growth mechanisms, surface incorporation sites, and arrangements of atoms at the lattice-scale. In this perspective, fractional crystallization modeling of 2011–2013 bulk rock data from lava fountains indicates that the compositional evolution of magmas erupted at Mt. Etna cannot be described by a unique equilibrium value of Di for a given clinopyroxene-melt interface. The leverage of interface kinetics is distinctively dominant along the subvolcanic plumbing system, thereby requiring that values of Di differ for structurally and compositionally distinct zones in clinopyroxene phenocrysts. To successfully interpret the trace element signature of Etnean magmas, the archetypal constancy of partition coefficient at bulk thermodynamic equilibrium must be in some measure reappraised in favor of the establishment of a local interface equilibrium upon highly dynamic crystallization and growth conditions.

Ethanol Dehydration to Ethylene over High-Energy Facets Exposed Gamma Alumina

Highly efficient and stable catalysts are among the key factors in industrial ethanol dehydration to ethylene. Among the widely studied catalysts, alumina is the most suitable for industrial application. In this study, novel gamma alumina was synthesized by solvent protection and a hydrothermal procedure. HRTEM, XRD, FT-IR, NH3-TPD, H-D exchange, and 29Si MAS NMR were employed to compare the difference in physicochemical properties between the novel gamma alumina and commercial alumina. Characterization results show that the as-synthesized novel gamma alumina mainly exposes the high-energy crystal plane (111) while the commercial alumina mainly exposes the thermostatically stable (110) crystal plane. The dominating (111) plane, according to the characterizations, endows the novel gamma alumina with a higher density of surface hydroxyl groups, higher acid content, and higher surface energy compared to the commercial alumina. The catalytic performance of the two catalysts for industrial ethanol dehydration to ethylene was studied. The novel (111) plane-exposed alumina showed a higher yield of ethylene than commercial alumina under the same reaction conditions. This could be related to the difference in atomic arrangement and the unsaturated aluminum coordination of different crystal planes. Stability testing under severe reaction conditions (450 °C, 1 MPa, 4 h−1) indicates that novel gamma alumina shows better stability (catalyst life cycle increased by 50%) and produces less acetaldehyde as a byproduct. The effects of steam treatment on the catalytic performance were further investigated. The surface acidity and the catalytic performance of novel gamma alumina present a volcanic curve with the increase in steam treatment temperature. Under the optimal water vapor treatment temperature of 650 °C, the conversion of ethanol and selectivity of ethylene were both higher than 99%.

Revealing impacts of electrolyte speciation on ionic charge storage in aluminum-quinone batteries by NMR spectroscopy

Rechargeable aluminum-organic batteries are composed of earth-abundant, sustainable electrode materials while the molecular structures of the organic molecules can be controlled to tune their electrochemical properties. Aluminum metal batteries typically use electrolytes based on chloroaluminate ionic liquids or deep eutectic solvents that are comprised of polyatomic aluminum-containing species. Quinone-based organic electrodes store charge when chloroaluminous cations (AlCl2+) charge compensate their electrochemically reduced carbonyl groups, even when such cations are not natively present in the electrolyte. However, how ion speciation in the electrolyte affects the ion charge storage mechanism, and resultant battery performance, is not well understood. Here, we couple solid-state NMR spectroscopy with electrochemical and computational methods to show for the first time that electrolyte-dependent ion speciation significantly alters the molecular-level environments of the charge-compensating cations, which in turn influences battery properties. Using 1,5-dichloroanthraquinone (DCQ) for the first time as an organic electrode material, we utilize solid-state dipolar-mediated and multiple-quantum NMR experiments to elucidate distinct aluminum coordination environments upon discharge that depend significantly on electrolyte speciation. We relate DFT-calculated NMR parameters to experimentally determined quantities, revealing insights into their origins. The results establish that electrolyte ion speciation impacts the local environments of charge-compensating chloroaluminous cations and is a crucial design parameter for rechargeable aluminum-quinone batteries.

Disordered interfaces of alkaline aluminate salt hydrates provide glimpses of Al3+ coordination changes

HypothesisThe precipitation and dissolution of aluminum-bearing mineral phases in aqueous systems often proceed via changes in both aluminum coordination number and connectivity, complicating molecular-scale interpretation of the transformation mechanism. Here, the thermally induced transformation of crystalline sodium aluminum salt hydrate, a phase comprised of monomeric octahedrally coordinated aluminate which is of relevance to industrial aluminum processing, has been studied. Because intermediate aluminum coordination states during melting have not previously been detected, it is hypothesized that the transition to lower coordinated aluminum ions occurs within ahighly disordered quasi-two-dimensional phase at the solid-solution interface. Experiments and simulationsIn situ X-ray diffraction (XRD), Raman and27Al nuclear magnetic resonance (NMR) spectroscopy were used to monitor the melting transition of nonasodium aluminate hydrate (NSA, Na9[Al(OH)6]2·3(OH)·6H2O). A mechanistic interpretation was developed based on complementary classical molecular dynamics (CMD) simulations including enhanced sampling. A reactive forcefield was developed to bridge speciation in the solution and in the solid phase. FindingsIn contrast to classical dissolution, aluminum coordination change proceeds through a dynamically stabilized ensemble of intermediate states in a disordered layer at the solid-solution interface. In both melting and dissolution of NSA, octahedral, monomeric aluminum transition through an intermediate of pentahedral coordination. The intermediate dehydroxylates to form tetrahedral aluminate (Al(OH)4−) in the liquid phase. This coordination change is concomitant with a breaking of the ionic aluminate-sodium ionlinkages. The solution phase Al(OH)4− ions subsequently polymerize into polynuclear aluminate ions. However, there are some differences between bulk melting and interfacial dissolution, with the onset of the surface-controlled process occurring at a lower temperature (∼30 °C) and the coordination change taking place more gradually as a function of temperature. This work to determine the local structure and dynamics of aluminum in the disordered layer provides a new basis to understand mechanisms controlling aluminum phase transformations in highly alkaline solutions.

Effects of anion incorporation on the local structure of porous-type amorphous alumina prepared by anodization: NMR study of Al coordination numbers

Although anodization is an essential technology that has supported the aluminum industry for nearly a century, the atomistic structure of the formed alumina films has not completely understood. Here we used NMR spectroscopy to clarify the factors affecting local structure of anodic porous alumina films prepared under various electrolytic conditions. For anion-free amorphous alumina films prepared using chromic acid, the local structure does not depend on electrolytic factors. For films prepared using phosphoric acid, the average coordination number was lower than that of anion-free alumina. On the other hand, films prepared using oxalic and sulfuric acids showed the average coordination numbers higher than that of anion-free alumina. We reveal that aluminum coordination number of anodic porous alumina are affected by anion species and anion content. In addition, the depth of anion incorporation into cell walls, or compositional uniformity, is quite important for accurate interpretation of NMR spectra.

Atomic and Electronic Structure of the Al2O3/Al Interface during Oxide Propagation Probed by Ab Initio Grand Canonical Monte Carlo.

Identifying the structure of the Al2O3/Al interface is important for advancing its performance in a wide range of applications, including microelectronics, corrosion barriers, and superconducting qubits. However, beyond the study of a few select terminations of the interface using computational methods, and top-down, laterally averaged spectroscopic and microscopic analyses, the explicit structure of the interface and the initial stages of propagation of the interface into the metal are largely unresolved. In this study, we utilize ab initio grand canonical Monte Carlo to perform a physically motivated, unbiased exploration of the interfacial composition and configuration space. We find that at equilibrium, the interface is atomically sharp with aluminum vacancies and propagates in a layer-by-layer fashion, with aluminum excess in the oxide layer at the interfacial plane. Oxygen incorporation, aluminum vacancy formation, and aluminum vacancy annihilation are the building blocks of Al2O3 formation at the interface. The localized interfacial mid-gap states from under-coordinated aluminum atoms from the oxide and the immediate depletion of aluminum states near the Fermi level upon oxygen incorporation prevent oxygen dissolution ahead of the interface front and result in the layer-by-layer propagation of the interface. This is in sharp contrast to the ZrO2/Zr system, which forms interfacial sub-oxides, and also explains the favorable self-healing nature of the Al2O3/Al system. The occupied interfacial mid-gap states also increase the calculated n-type Schottky barrier heights. Additionally, we identify that interfacial aluminum core-level shifts linearly depend on the aluminum coordination number, whereas interfacial oxygen core-level shifts depend on long-range ordering at the interface. The detailed geometric and electronic insights into the interface structure and evolution expand our understanding of this fundamental interface and have important implications for the engineering and design of Al2O3/Al-based corrosion coatings with enhanced barrier properties, controllable transistor technologies, and noise-free superconducting qubits.

Dynamic Evolution of Aluminum Coordination Environments in Mordenite Zeolite and Their Role in the Dimethyl Ether (DME) Carbonylation Reaction

Part of tetrahedral framework aluminum in a protonic mordenite (HMOR) will convert geometry to distorted tetrahedral and octahedral coordination. High-field 27 Al NMR data show that more framework Al atoms at T3 and T4 sites change geometry to nonframework structures than others. These nonframework Al species preferentially reside in the side pockets, which will decrease the accessibility of acid sites in the 8-membered ring (MR) channel, impairing the dimethyl ether (DME) carbonylation reaction. The arisen octahedrally coordinated Al species are framework-associated, which can be reverted into the zeolite framework. Herein, we find that a facile treatment with pyridine could force the octahedral coordination Al back into a tetrahedral environment, which could increase the number of available active sites and enhance the diffusion of DME, thus improving the reactivity (4 times) of the DME carbonylation reaction and prolonging the lifetime of catalysts.

Dynamic Evolution of Aluminum Coordination Environments in Mordenite Zeolite and Their Role in the Dimethyl Ether (DME) Carbonylation Reaction

AbstractPart of tetrahedral framework aluminum in a protonic mordenite (HMOR) will convert geometry to distorted tetrahedral and octahedral coordination. High‐field 27Al NMR data show that more framework Al atoms at T3 and T4 sites change geometry to nonframework structures than others. These nonframework Al species preferentially reside in the side pockets, which will decrease the accessibility of acid sites in the 8‐membered ring (MR) channel, impairing the dimethyl ether (DME) carbonylation reaction. The arisen octahedrally coordinated Al species are framework‐associated, which can be reverted into the zeolite framework. Herein, we find that a facile treatment with pyridine could force the octahedral coordination Al back into a tetrahedral environment, which could increase the number of available active sites and enhance the diffusion of DME, thus improving the reactivity (4 times) of the DME carbonylation reaction and prolonging the lifetime of catalysts.