Aluminum Species Research Articles

Regeneration and Single Stage Batch Adsorber Design for Efficient Basic Blue-41 Dye Removal by Porous Clay Heterostructures Prepared from Al13 Montmorillonite and Pillared Derivatives.

Porous clay heterostructures are a hybrid precursor between the pillaring process and organoclays. In this study, the organoclay was substituted by an aluminium intercalated species clay or pillared alumina clays. A porous clay heterostructure was successfully achieved from an aluminium intercalated species clay, due to the easy exchange of the aluminium species by the cosurfactant and silica species. However, using alumina pillared clays, the porous clay heterostructures were not formed; the alumina species were strongly attached to clay sheets which made difficult their exchange with cosurfactant molecules. In this case, the silica species were polymerized and decorated the surface of the used materials as indicated by different characterization techniques. The specific surface area of the porous clay heterostructure material reached 880 m2/g, and total pore volume of 0.258 cc/g, while the decorated silica alumina pillared clays exhibited lower specific surface area values of 244-440 m2/g and total pore volume of 0.315 to 0.157 cc/g. The potential of the synthesized materials was evaluated as a basic blue-41 dye removal agent. Porous clay heterostructure material has a removal capacity of 279 mg/g; while the other materials exhibited lower removal capacities between 75 mg/g and 165 mg/g. The used regeneration method was related to the acidity of the studied materials. The acidity of the materials possessed an impact on the adopted regeneration procedure in this study, the removal efficiency was maintained at 80% of the original performance after three successive regeneration cycles for the porous clay heterostructure. The Langmuir isotherm characteristics were used to propose a single-stage batch design. Porous clay heterostructures with a higher removal capacity resulted in a decrease in the quantities needed to achieve the target removal percentage of the BB-41 dye from an aqueous solution.

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.

Enhanced Removal of Refractory Organic Compounds from Coking Wastewater Using Polyaluminum Chloride with Coagulant Aids

This study explores the enhanced removal of refractory organic compounds from coking wastewater using polyaluminum chloride (PACl) with two different basicity levels (0.5 and 2.5), in combination with coagulant aids such as cationic polyacrylamide (CPAM) and iron ions. The results demonstrated that both PACl formulations significantly outperformed commercial PACl in terms of COD and color removal, with PACl at the basicity of 2.5 achieving slightly higher efficiency than PACl at the basicity of 0.5. The improved performance was attributed to the higher content of polymeric aluminum species, enhancing charge neutralization and bridging adsorption. The addition of coagulant aids further improved the performance, with PACl at the basicity of 2.5 combined with iron ions achieving the highest COD (48.41%) and color removal (80.77%), due to sweep coagulation and complexation. Organic composition analysis using gas chromatography–mass spectrometry (GC-MS), three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy, and ultraviolet (UV) spectroscopy indicated that PACl combined with iron ions was the most effective in removing polycyclic aromatic hydrocarbons (PAHs) and nitrogen-, oxygen-, and sulfur-containing heterocyclic compounds. Additionally, a floc analysis showed that the flocs formed with iron ions were more compact and had better settleability compared to those formed with CPAM, further contributing to the improved coagulation efficiency. These results highlight the importance of optimizing the PACl basicity and coagulant aid selection for the enhanced removal of refractory organic compounds from coking wastewater, offering a promising strategy for advanced wastewater treatment.

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.

Causes of negatively charged meso-colloids formed in the coagulation process: Implication of the origin of foulants in the coagulation–membrane filtration process

Tiny colloids with a size similar to that of membrane pores are responsible for irreversible fouling in the pre-coagulation microfiltration membrane filtration process for drinking water treatment. Such colloidal particles are defined here as meso‑colloids, and the charge neutralization of meso‑colloids is demonstrated to be a key to controlling irreversible fouling. However, meso‑colloids remain negatively charged at neutral pH, the reason for which is still unclear. To increase the efficiency of membrane operation, additional knowledge about the causes and behaviors of meso‑colloids during pre-coagulation is indispensable. Therefore, in this study, meso‑colloids are fractionated after a series of jar tests, and their exact composition and charge properties are characterized. Two natural water samples, the adjusted water consisting of meso‑colloid fraction separated from one of the natural water samples and additional inorganic chemicals, and the adjusted water by the addition of appropriate inorganic chemicals into pure water are used for jar tests, which are conducted with and without the addition of the coagulant polyaluminum chloride (PACl). After the jar tests using two natural water samples, all of the meso‑colloids exhibit a negative charge under the conditions applied for the jar tests, indicating that charge neutralization is difficult. The composition of the meso‑colloids is found to be completely different depending on the water source used. Organic-rich water tends to generate meso‑colloids with a low Al/C (mass ratio of aluminum and organic carbon) ratio. In contrast, organic-poor water tends to produce meso‑colloids with a high Al/C ratio. From the results of the jar tests using two kinds of adjusted water samples, it is found challenging to neutralize meso‑colloids by PACl at neutral pH, because the overdose and underdose of PACl result in negatively charged biopolymer or negatively charged aluminum species. Therefore, the development of a new coagulant for specific use in the coagulation membrane filtration process is proposed, which can minimize the formation of negatively charged species even at neutral pH.

Influence of Extra-Framework Aluminum Species on the Catalytic Properties of Acidic USY Zeolite in (Hydro)cracking Reactions

Influence of Extra-Framework Aluminum Species on the Catalytic Properties of Acidic USY Zeolite in (Hydro)cracking Reactions

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.

Synthesis of CHA zeolite in phenoxide media for CO2 capture

Synthesis of small-pore chabazite (CHA) zeolites in the absence of organic structure-directing agents (OSDA) has been proven difficult. A judicious mixed cation approach recently reported could expand the design space of CHA formation. In a seemingly opposite direction, we herein report an anion tuning approach for controlling the zeolite polymorphism in an OSDA-free system that effectively promotes hierarchical CHA formation in a competitive growth with MER. Phenoxide media, utilizing mild in-situ nucleophilic etching in cooperation with zeolite framework growth, allow beneficial kinetic control to facilitate CHA nucleation. Operando analyses reveal the crucial role of stabilized dimeric aluminate species as a key intermediate for CHA phase selection. The phenol-mediated CHA zeolites exhibit almost perfect 9 molecules per unit cell CO2 uptake capacity and no CH4 adsorption. This work offers an anion tuning strategy for controlling zeolite polymorphism as a supplement to the current phase-selection toolbox that utilizes mixed inorganic cations.

Capacity building in porous materials research for sustainable energy applications.

The project aimed to develop porous materials for sustainable energy applications, namely, hydrogen storage, and valorization of biomass to renewable fuels. At the core of the project was a training programme for Africa-based researchers in (i) the exploitation of renewable locally available raw materials; (ii) the use of advanced state-of-the-art techniques for the design and synthesis of porous materials (zeolites and metal-organic frameworks (MOFs)) for energy storage; and (iii) the valorization of sustainable low-value feedstock to renewable fuels. We found that compaction of the UiO-66 MOF at high pressure improves volumetric hydrogen storage capacity without any loss in gravimetric uptake, and experimentally demonstrated the temperature-dependent dynamic behaviour of UiO-66, which allowed us to propose an activation temperature of ≤ 150°C for UiO-66. Co-pelletization was used to fabricate UiO-66/nanofibre monoliths as hierarchical porous materials with enhanced usable (i.e. deliverable) hydrogen storage capacity. We clarified the use of naturally occurring kaolin as a source of silica and alumina species for zeolite synthesis. The kaolin-derived zeolite X was successfully used as a catalyst for the transesterification of Jatropha curcas oil (from non-edible biomass) to biodiesel. We also prepared porous composites (i.e. carbon/UiO-66, organoclay/UiO-66 and zeolite/carbon) that were successfully applied in electrochemical sensing.

Revisited Synthesis of Trispyrazolylborate Aluminum Halides Suban Kundu, Raju Chambenahalli, Alex P. Andrews and Ajay Venugopal*

Tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2 (X=Cl, Br and I) can be potential precursors for preparing highly electrophilic dications as well as low oxidation state aluminum compounds. However, the coordinative unsaturation in TpMe2AlX2 makes them susceptible to rearrangement to [Tp2Al][AlX4]. In this work, we revisited the synthesis of TpMe2AlX2 by isolating the solvent‐stabilized tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2(L) (X=Cl, Br; L = THF, HPMA). Efforts to isolate TpMe2All2 resulted in the ring opening of THF revealing the mediation of a highly reactive cationic aluminum species. The monocationic, [TpMe2AlCl(THF)2][B{C6H3(CF3)2}4] was prepared from TpMe2AlCl2(THF) via silver salt metathesis. Attempts to prepare the dicationic species [TpMe2Al(THF)3]2+ resulted in the instantaneous ring‐opening polymerization of THF.

Direct evidence for the mechanism of early-stage geopolymerization process

Geopolymer, an alternative construction material to cement, acquires strength and endurance through the geopolymerization process. However, the study on the early-stage geopolymerization is rare since it occurs rapidly and involves liquid phase, viscous slurry, and gel-like material, making the observation of this process complicated. This research addresses the challenge of observing this process by providing real-time evidence through in situ techniques: Fourier-transformed infrared (FTIR) spectroscopy, X-ray absorption spectroscopy (XAS), and environmental scanning electron microscopy (E-SEM). These methods consistently confirm the formation of aluminosilicate oligomers, short chains of silicate and aluminate species, in the polycondensation Stage I within the initial 5 minutes. This stage involves the reaction of Si-O and Al-O monomers, released during a dissolution process, with available Na2SiO3 from alkaline solutions in the system. In the subsequent polycondensation Stage II, aluminosilicate oligomers polymerize, creating a three-dimensional network of aluminosilicate chains through the crosslinking of Si-O-Si and Si-O-Al bonds. This process continues beyond the initial 5 minutes, gradually nearing completion around 30 minutes, as consistently confirmed by various experimental techniques. Rheological studies on the geopolymer paste flow rate support these interpretations. The study provides compelling direct evidence into the mechanisms of early-stage geopolymerization, significantly contributing to the research field and paving the way for widespread utilization in geopolymer applications.

Al-Based MOF-Derived Amorphous/Crystalline Heterophase Cobalt Sulfides as High-Performance Supercapacitor Materials.

Transition metal sulfides (TMSs) are promising electrode materials due to their high theoretical specific capacitance, but sluggish charge transfer kinetics and an insufficient number of active sites hamper their applications in supercapacitors. In this work, a self-sacrificial template strategy was employed to construct Al-based MOF-derived metal sulfides with an amorphous/crystalline (a/c) heterophase, in which aluminum, nitrogen, and carbon species were evenly coordinated in the amorphous phase. The metal sulfides a/c-Co(Al)S-1 and a/c-Co(Al)S-2, originating from the CAU-1 and CoAl-MOF on NF as self-sacrificial templates, were investigated as electrode materials, respectively, in which the a/c-Co(Al)S-1 showed a more excellent electrochemical performance. Through acid etching CAU-1 using Co(NO3)2 followed by sulfuration, the a/c-Co(Al)S-1 with a unique 3D network structure was constructed, whose unique architecture expanded the interfacial contact with the electrolyte and provided vast active sites, accelerating the charge transportation and ion diffusion. Notably, the a/c-Co(Al)S-1 displayed a high specific charge of 1791.8 C g-1 at 1 A g-1, satisfactory cycle stability, and good rate capability. The corresponding assembled a/c-Co(Al)S-1//AC device delivered a high energy density of 77.1 Wh kg-1 at 800 W kg-1 and good durability (87.4% capacitance retention over 10 000 cycles).

Mesoporous carbon hollow spheres with controllable pore structure for efficient lithium and aluminum ion storage

Mesoporous carbon hollow nanospheres (MCHS), synthesized via a block copolymer-mediated supramolecular self-assembly process, serve as both anode materials for lithium-ion batteries (LIBs) and cathode materials for aluminum-ion batteries (AIBs). By adjusting the carbonization temperature and the dosage of the pore extender, 1,3,5-trimethylbenzene (TMB), insights into the relationships among pore structure, crystal structure, and electrochemical properties of MCHS in Li/Al-ion batteries are gained. Their exceptional properties, including hierarchically porous structure, large surface area, tailored inner voids, mesoporous shells, and high electronic conductivity, contribute to high specific capacity, improved rate performances, and remarkable electrochemical stability. Crystallographic insights reveal that highly porous MCHS facilitate the intercalation of ionic lithium and aluminum species into the carbon crystal lattices while maintaining structural integrity. The appropriate mesopore size significantly impacts the storage of lithium or aluminum ions, with relatively larger mesopore sizes being more beneficial for aluminum ion storage compared to lithium ions. The optimal MCHS exhibit a stable discharge specific capacity of 330.8 mAh·g−1 after 800 cycles at a current density of 372 mA·g−1 (1C) in LIBs and 41.6 mAh·g−1 after 500 cycles at 74.4 mA·g−1 in AIBs.

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.

Regulating the coordination environment of surface alumina on NiMo/Al2O3 to enhance ultra-deep hydrodesulfurization of diesel

Herein, a set of NiMo/Al2O3 catalysts with distinct coordination state of surface alumina were design and prepared by a facile calcination strategy. Various characterization methods were employed to analyze the structural properties of NiMo/Al2O3 catalysts, and the catalytic performances of corresponding catalysts were tested for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The results indicate that the synthesized samples show uniform specific surface area (130 m2·g−1) and pore size (3.5 nm), but varying penta-coordinated aluminum content, which significantly influences the NiMo/Al2O3 catalysts’ surface acidity. Therein, NiMo/Al2O3-600 prepared by calcination at 600 °C exhibits the highest ratio of penta-coordinated aluminum species, which endows more abundant Brønsted acid than that of tetra- and hexa-coordinated aluminum counterparts, thereby substantially promoting the isomerization and direct desulfurization pathways of 4,6-DMDBT HDS, and thereafter considerably boosting the HDS performance of NiMo/Al2O3-600 with 94.5 % 4,6-DMDBT conversion, which is notably higher than that of NiMo/Al2O3-500 (74.4 %) and NiMo/Al2O3-700 (62.7 %).

Modulation of aluminum species in mordenite zeolite for enhanced dimethyl ether carbonylation

Dimethyl ether (DME) carbonylation is an important intermediate step in the synthesis of methyl acetate (MA) and ethanol. H-form mordenite (MOR) can efficiently catalyze the reaction, in which Brønsted acid sites (BASs) associated with framework Al function as active sites. But the role of other Al species such as exteraframework Al (EFAl) and framework-associated Al still remains unknown. In this study, we have proposed two convenient approaches for controlling the two Al species and investigating their influence on the DME carbonylation reaction. NH3-TPD and Py-IR analyses revealed that the number of BASs increased after the removal of EFAl and the inhibition the formation of framework-associated Al. The reactivity results showed that the elimination of EFAl promoted the DME conversion from 28% to 46%. Additionally, through the implementation of in-situ calcination to impede the presence of framework-associated Al, the DME conversion increased from 28% to 50%. With the understanding that both EFAl and framework-associated Al have a detrimental effect on the reaction, the highest conversion is achieved with these two treatments, leading to 73% DME conversion with 99% selectivity to MA. Our findings provide a systematical strategy to effectively regulate the presence of Al species in zeolite, offering insights of rational design to optimize zeolite catalysts for important industrialized process.

Monitoring the Degradation of Metal‐Organic Framework Drug Nanocarriers by In‐Situ NMR Spectroscopy

AbstractAn accurate characterization methodology is indispensable to design nanoparticle‐based drug delivery system (DDS) adapted to specific diseases and therapies. However, characterization techniques employed to investigate drug release and nanoparticle degradation require separating the nanoparticles from their suspension media, which can lead to artefacts. Therefore, there is a clear need to implement novel versatile in‐situ methods. Here, we report the use of in‐situ NMR spectroscopy to monitor drug delivery processes from MOF nanocarriers, both in solution and in the solid state simultaneously. In‐situ 1H NMR investigation of nanoMIL‐100(Al) suspension in phosphate medium enabled recording the trimesate ligand loss in the solid phase and the ligand release in the liquid phase as a function of time. Simultaneously, 27Al NMR enabled assessing the progressive replacement of carboxylate ligands by phosphates leading to the formation of new aluminum species. Using the same strategy, we also compared the degradation of nanoMIL‐100(Al) loaded with two drug analogs, highlighting an effect of metal‐ligand complexing strength. Furthermore, our in‐situ technique is applicable to studying the reaction of paramagnetic nanoMIL‐100(Fe) in the liquid phase. This work offers an alternative to ex‐situ techniques for understanding the degradation mechanism of MOF nanocarriers and could be an asset for other nanoscale DDSs.

Structural Aspects of Ambient-Temperature Densification of Highly Crack-Resistant Borosilicate and Aluminoborosilicate Glasses: Two Case Studies Examined by Solid-State NMR.

The structural aspects of ambient-temperature densification via pressurization at 25 GPa were studied by solid-state NMR for two case studies: An alkaline earth boroaluminosilicate glass with the composition 6CaO-3SrO-1BaO-10Al2O3-10B2O3-70SiO2 (labeled SAB) and a sodium magnesium borosilicate glass with the composition 10Na2O-10MgO-20B2O3-60SiO2 (labeled MNBS). For SAB glass, cold pressurization results in significant increases in the average coordination numbers of both boron and aluminum, in line with previous results found in hot-compressed alkali aluminoborosilicate glasses. In addition, 27Al/11B dipolar recoupling experiments reveal a significant decrease in the 11B/27Al dipolar interaction strength upon pressurization, suggesting that the higher-coordinated boron and aluminum species experience weaker magnetic interactions. While this is an expected consequence of the longer internuclear distances involving higher coordination states, the magnitude of the effect also is consistent with a decrease of average B-O-Al internuclear connectivity. By conjecture, a decreased B-O-Al connectivity may present a mechanism of plastic flow inhibiting crack initiation in aluminoborosilicate glasses. In the case of the MNBS glass, no change in the average boron coordination number was observed within experimental error; however, densification increases the extent of B-O-Si connectivity at the expense of small ring structures with dominant B-O-B connectivity. With regard to boron coordination, the data obtained for both case studies differ from those previously found in a series of alkali borosilicate glasses, which had shown an unexpected decrease in N4 upon increased pressure. The results of the present study highlight the importance of changes of medium-range order regarding densification.

Synergistic effect of the framework boron and Al-rich region to enhance the metal-support interaction for boosting Pd-based catalyst activity of dimethyl carbonate synthesis

Efficient production of dimethyl carbonate (DMC) from methyl nitrite (MN) carbonylation based on PdCu/NaY zeolite catalysts is highly desired for industrial applications. The introduction of boron species into the initial gels of NaY synthesis is a cost-effective modification strategy for boosting the catalytic performance. It not only introduces trace amounts of framework boron but also regulates the distribution of framework aluminum (AlF) species. Most importantly, the synergistic effect of framework boron and Al-rich region significantly enhanced the metal − support interaction, thus promoting more electrons to be transferred from metal to support. This strategy allows the palladium active species to remain in an electron-deficient state more easily. The carbon monoxide (CO) adsorption and the critical intermediate species *CH3COO are more easily formatted on PdCu/NaBY catalyst, which leads to superior weight-time yields (WTYDMC up to 1507·g·kgcat − 1·h− 1), and CO conversion to DMC (CCO up to 83 %). Our design is of great importance for developing metal-zeolites catalysts, which motivates the industrial application of Pd-based catalysts in the MN carbonation of DMC field.