Al Distribution Research Articles

Effect of Al Distribution in MFI Framework Channels on the Catalytic Performance of Ethane and Ethylene Aromatization

The relationship between the formation of aromatics in catalytic ethane/ethylene aromatization and Al distribution in Mobil-type five (MFI) channel was investigated using ZSM-5 zeolites with contro...

Bulk structures of silica-rich calcium aluminosilicate (CAS) glasses along the molar CaO/Al2O3 = 1 join via molecular dynamics (MD) simulation

In order to understand how surface charge accumulation and other reactivity-related phenomena are controlled by the surface structure, it is necessary to have a detailed appreciation of the bulk glass structures. Here, we report a detailed MD study of the bulk structures of silica-rich calcium aluminosilicate (CAS) glasses along the tecto-silicate join.It is confirmed that the structures of these glasses contain small concentrations of over- and under-coordinated defect species, such as NBO, TBO and [5]-coordinated aluminum, AlC5, in contrast to the simple idea that these fully charge-compensated compositions, with Ca/Al2O3 ratios of unity, should have fully polymerized structures. The Si,Al distribution was found to be largely random (i.e. Lowenstein's rule is not obeyed) and no significant segregation of Ca to Al was observed.Interactions between TBO and AlC5 were manifest both in the presence of an additional small peak in the Al-O-Al BAD and in the formation of structural complexes involving small-membered rings, particularly 2-rings. These defect structural complexes contributed to the structural inhomogeneity of these glasses.

Enhanced luminescence in rare-earth-free fast-sintering glass-ceramic

One of the major challenges pursued in the luminescent materials community is to develop rare-earth-free phosphors in order to reduce the use of rare-earth elements, because of the lack of their availability and the environmental problems derived from their mining and processing. In this work, a rare-earth-free glass-ceramic-based phosphor with high photoluminescence has been designed. This novel phosphor rich in Na-rich plagioclase feldspar crystallizations presents high crystallinity, ∼94%, and a dual micro-nanostructure provided by a fast-sintering processing route. Structural disorder in Si–Al distribution favors formation of luminescent centers in the glass-ceramic material, which results in an enhancement of both the UV–blue and the red luminescence regarding natural feldspars, 1 order of magnitude and 6 times, respectively. A microstructural and structural study by means of x-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, cathodoluminescence, and nuclear magnetic resonance evidence the important role of composition in the alteration of Si–Al ordering schemes. A strong correlation between Si–Al disorder and the presence of active luminescent centers is corroborated. Our research shows a sustainable, cost-effective, innovative, and scalable material that may be considered as an alternative to rare-earth phosphors for applications such as security markers or light-emitting glasses. This novel family of rare-earth-free glass-ceramics opens a new gate through structural tailoring to enhance and tune the intrinsic luminescent emissions displayed for relevant future optical applications.

Cooperative Role of Water Molecules during the Initial Stage of Water-Induced Zeolite Dealumination

Understanding water-induced zeolite dealumination is crucial for control of the hydrothermal stability of zeolite-based catalyst materials. Here we explore the dealumination process, focusing on the first Al–O(H) bond-breaking step in a density functional theory model of a ZSM-5 crystal in the presence of a single and two water molecules per active site. We identify a set of four possible reaction mechanisms consisting of two different types of reactions. In the first three proposed mechanisms, Al–O(H) bond breaking is induced by adsorption and dissociation of an incoming water molecule. The fourth mechanism is different and leads to a different reaction product, suggesting an alternative follow-up mechanism. In this energetically very favorable case, the breaking of the Al–O(H) bond is induced by nondissociative adsorption of two water molecules. We therefore assume that the proposed mechanism is a viable first dealumination step. This implies that all Al–O(H) bond-breaking mechanisms are initiated from metastable water adsorption modes, and water reorganization from the most stable mode needs to occur prior to hydrolysis of the Al–O(H) bond. We suggest that the feasibility of this rearrangement (Al accessibility) is one of the determining factors for the relative occurrence of dealumination at different sites. We further establish a correlation between the Al site susceptibility toward dealumination and reaction conditions, which can be further used during postsynthetic treatment of the zeolite to control Al distribution and thus hydrothermal stability of the catalyst.

Effect of B and Al Distribution in ZSM-5 Zeolite on Methanol to Propylene Reaction Performance

Effect of B and Al Distribution in ZSM-5 Zeolite on Methanol to Propylene Reaction Performance

Insight into the impact of Al distribution on the catalytic performance of 1-octene aromatization over ZSM-5 zeolite

To correlate the relationship between the Al distribution and the catalytic performance of long-chain olefin aromatization, several ZSM-5 zeolites with different Al locations and proximities were prepared via adjusting the hydrothermal synthesis conditions.

Tracking the rearrangement of atomic configurations during the conversion of FAU zeolite to CHA zeolite.

In order to realize designed synthesis, understanding the formation mechanism of zeolites at an atomic level has long been aspired, but remains challenging due to the fact that the knowledge of atomic configurations of the species formed during the process is limited. We focus on a synthesis system that crystallizes CHA zeolite from FAU zeolite as the sole source of tetrahedral atoms of Si and Al, so that end-to-end characterization can be conducted. Solid-state 29Si MAS NMR is followed by high-throughput computational modeling to understand how atomic configurations changed during the interzeolite conversion. This reveals that the structural motif commonly found in FAU and CHA is not preserved during the conversion; rather, there is a specific rearrangement of silicates and aluminates within the motif. The atomic configuration of CHA seems to be influenced by that of the starting FAU, considering that CHA synthesized without using FAU results in a random Al distribution. A Metropolis Monte-Carlo simulation combined with a lattice minimization technique reveals that CHA derived from FAU has energetically favorable, biased atomic locations, which could be a result of the atomic configurations of the starting FAU. These results suggest that by choosing the appropriate reactant, Al placement could be designed to enhance the targeted properties of zeolites for catalysis and adsorption.

Tuning the Aluminum Distribution in Zeolites to Increase their Performance in Acid-Catalyzed Reactions.

The organization of Al atoms in the framework of Si-rich zeolites is very important and includes two classes: (i) the Al siting that determines which individual, crystallographically distinguishable framework T sites are occupied by Al atoms and (ii) the Al distribution, which describes the relation of two or more Al atoms in the framework, their distances, and the possibility of neighboring Al atoms to cooperate in the formation of active sites. The organization of Al significantly affects the catalytic properties of Si-rich, zeolite-based catalysts in acid and redox catalysis. Herein, what is known about the organization of Al in the framework of industrially very important pentasil-ring Si-rich zeolites (ZSM-5, beta zeolite, mordenite, ferrierite, MCM-22, and TNU-9), as well as the very promising SSZ-13 Si-rich zeolite with the CHA structure, is summarized.

Disentanglement of the secrets of aluminium in acidophilic tea plant (Camellia sinensis L.) influenced by organic and inorganic amendments

Field experiment was carried out for four years in mature tea (Camellia sinensis L.) growing plot to investigate the impacts of different doses of inorganic and organic fertilizers on aluminium (Al) distribution pattern in soil and different parts of tea plant, leaf pigment concentration, gas exchange parameters, as well as the yield of tea. Results indicated that application of 6 × 103 kg compost ha−1 significantly increased the dry matter yields of tea. Pluckable shoot of tea plant were markedly stimulated in the presence of Al irrespective of treatment imposed. Furthermore, Al induced growth stimulation in tea plant was facilitated by higher photosynthesis rate as well as gas exchange parameters. For the present experiment, Tea Research Association Heavy Metal Contamination Index (TRAHMCI) decreases with increase the fertilizer dose and all the experimental soils were found non-polluted with respect to Al. Localization of Al in the root apex predominantly accumulated in the cortex. The translocation of Al from root to shoot was driven by the gradient in hydrostatic pressure and water potential. In all tea infusions influenced by different treatments, Al concentrations were within the maximum permissible limit of Al in drinking water by Provisional Tolerable Weekly Intake (PTWI) established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA, 2 mg kg−1 bw−1) and the tolerable weekly intake (TWI) established by EFSA (European Food Safety Authority, 1 mg kg−1 bw−1). Application of stepwise multiple regression model indicates that around 75% of the variability in the yield of the crop can be expressed by the selected parameters under study. The Hierarchical cluster analysis reveals that two homogenous groups of treatment can be formed based on all the studied parameters.

Alleviation of aluminum phytotoxicity by canola straw biochars varied with their cultivating soils through an investigation of wheat seedling root elongation

The types and amounts of cations and their uptake by plants vary with cultivating soils, which correlates with the carbonates and subsequent alkalis contents in the derived biochars. However, regional differences in the alkaline properties of crop straw biochars are unclear. In the present study, biochars pyrolyzed from canola straws collected from four different regions were used to assess the differences in the alkaline properties among them. The biochars were referred to as YTBC, XCBC, NJBC, and HYBC, respectively, and their feedstocks were collected from four different regions from south to north of China. The NH4OAC exchangeable base cations (K+, Na+, Ca2+, Mg2+) in the biochars were 270.74, 1427.05, 2089.23, and 1516.48 mmol kg−1 for YTBC, XCBC, NJBC, and HYBC, respectively, which were roughly consistent with the exchangeable base cations in the corresponding planting soils (17.57, 28.20, 151.26 and 444.65 mmol kg−1, respectively). The pH, carbonates content, and alkalinity of biochars considerably increased as follows: YTBC < XCBC < NJBC < HYBC. Wheat seedling root elongation experiment indicated that the Al(III) phytotoxicity alleviation effect of the biochars was as follows: HYBC > NJBC > XCBC > YTBC, which was corroborated by the subsequent findings of Evans blue staining, the remnant aluminum (Al(III)) in the reaction solution and Al(III) distribution in the wheat seedling roots. Thus, planting soil had a dominant influence in alleviating Al(III) phytotoxicity, and studies on crop straw biochar properties concerning alkalinities or liming potentials should not only consider crop genera and pyrolysis conditions, but also cultivating conditions.

Al Organization in the SSZ-13 Zeolite. Al Distribution and Extraframework Sites of Divalent Cations

SSZ-13 is a Si-rich (Si/Al > 5) small pore zeolite (chabazite topology) important for both acid and redox catalysis. Using a sample with Si/Al = 12, a new procedure involving 27Al (3Q) MAS NMR spectroscopy and extensive periodic DFT calculations with molecular dynamics, in addition to the standard methods based on bare Co(II) cations as probes monitored by FTIR spectroscopy and UV–vis spectroscopy, was employed. The placement of the Al–O–(Si–O)2–Al and Al–O–(Si–O)3–Al sequences in the zeolite framework was determined (Al–O–Si–O–Al sequences are absent). 54% of the framework Al atoms correspond to Al–O–(Si–O)3–Al sequences which cannot form cationic sites for bare divalent cations but are able to accommodate divalent Co(II) hexaaqua complexes. The corresponding Al–O–(Si–O)3–Al sequence is located in two double 6-ring cages with one Al located in the 4-ring connecting two double 6-ring units. Our study also reveals that 35% of the framework Al atoms can accommodate neither divalent Co(II) hexaaqua complexes...

Electrochemical characterization of Raney nickel electrodes prepared by atmospheric plasma spraying for alkaline water electrolysis

A Raney Ni electrode was prepared by the simple and economical atmospheric plasma spraying method. It showed excellent performance for hydrogen evolution reaction (HER), as indicated by a Tafel slope of 54mV/dec and overvoltage of 108mV at 300mA/cm2. The Ni–Al alloy coating contained a NiAl phase, which has a very slow Al leaching rate in alkaline solution. H2 heat treatment of the electrode enhanced the uniformity of Al distribution in the coating and adhesion of the coating to the substrate. However, the HER performance did not improve and the electrode was rendered more structurally vulnerable to deactivation.

Making Nanosized CHA Zeolites with Controlled Al Distribution for Optimizing Methanol-to-Olefin Performance.

From theoretical calculations and a rational synthesis methodology, it has been possible to prepare nanocrystalline (60-80 nm) chabazite with an optimized framework Al distribution that has a positive impact on its catalytic properties. This is exemplified for the methanol-to-olefin (MTO) process. The nanosized material with the predicted Al distribution maximizes the formation of the required MTO hydrocarbon pool intermediates, while better precluding excessive diffusion pathways that favor the rapid catalyst deactivation by coke formation.

A half-type ABC transporter FeSTAR1 regulates Al resistance possibly via UDP-glucose-based hemicellulose metabolism and Al binding

Buckwheat (Fagopyrum esculentum) is highly tolerant to Al stress, but the molecular mechanisms remain largely unknown. This study aims to investigate a half-type ABC transporter gene (FeSTAR1) with respect to Al tolerance. The expression of FeSTAR1 was examined and complementation test in atstar1 mutant was conducted. Furthermore, Al distribution and cell wall polysaccharides content were analyzed. FeSTAR1 is an ABC transporter protein with nucleotide binding domain, but lack of transmembrane domain. Consistently, FeSTAR1 is a soluble protein, localizing to both cytoplasm and nucleus. Al rapidly and specifically induced FeSTAR1 expression. Heterologous expression of FeSTAR1 in atstar1 rescued its Al tolerance, and exogenous applied UDP-glucose could alleviate Al sensitivity of atstar1 mutant, suggesting the connection between FeSTAR1 and UDP-glucose in terms of Al tolerance. Furthermore, FeSTAR1 complemented lines accumulated less Al in root cell wall than atstar1 mutant. Further cell wall fraction analysis showed that Al was largely confined to cell wall hemicellulose1, at which Al content was significantly lower in complemented lines. Consistent with Al distribution in different cell wall polysaccharides, complemented lines had lower hemicellulose1 content. Our results indicate that FeSTAR1 is involved in Al resistance via possibly cell wall matrix polysaccharides metabolism in buckwheat.

Aluminum influence on Calotropis procera seedling growth, nutrient accumulation and electrochemical attributes

The effects of aluminium (Al) toxicity on Calotropis procera were investigated by exposing seedlings to nutrient solutions with concentrations of 0 (control), 15, 30, 45 and 60 mg/l respectively. Seedling growth, nutrient concentrations including Al, plant biomass and electrochemical impedance spectroscopy (EIS) were evaluated in one- month-old C. procera. Seedling growth traits (number of leaves, leaf / root length) and plant biomass (fresh and dry shoot and root weight) were significantly reduced in all Al treatments. Aluminium impaired the absorption and passage of certain nutrient elements (P), but stimulated others (Ca2+). An interesting trend was observed in the case of K+, which was observed to be increased in roots, decreased in stems and unaffected in leaves after an increase in Al concentration. Remarkable differences were also observed in Al concentration and distribution in different plant organs (roots, stems and leaves). During EIS measurements, Nyquist plots spectra (from 1 Hz – 1 MHz) demonstrated that the complex impedance (real and imaginary) was higher in leaves than in roots. The proposed Cole-Cole model fitted well with the measured impedance spectra. The model parameters [(resistance (R), capacitance (C)] differed between roots and shoots. In general, R1 (extracellular resistance) was higher in roots than in the leaves, but the opposite was true for R2 (intracellular resistance). Al significantly increased C1 (extracellular capacitance), with the highest concentrations observed in leaves rather than roots. We conclude that biophysical measurements in roots and leaves are useful for assessing aluminium toxicity in C. procera seedlings, and that roots / leaves have the potential to be tolerant against Al toxicity.

Bulk Li mobility enhancement in Spark Plasma Sintered Li(7−3x)AlxLa3Zr2O12 garnet

Li(7−3×)AlxLa3Zr2O12 (LLAZO) Al-doped garnets display high ionic conductivity in the range of ~ 10−4 S.cm−1 at room temperature and are thus envisioned for future solid-state batteries. In this study, LLAZO powders with two doping levels were synthetized using a solid-state route and sintered using Spark Plasma Sintering (SPS). Both pristine and SPS crushed pellet powders were investigated using X-Ray Diffraction (XRD) confirming the formation of the most conducting cubic phase. Ionic conductivity measurements were performed using electrochemical impedance spectroscopy. Li and Al distributions among available sites were identified using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, and Li mobility was explored using 7Li static wideline NMR spectroscopy. Results show that SPS treatment, beyond producing highly densified pellets, mainly modifies Al distribution and strongly impacts the bulk Li+ mobility.

Controllable synthesis of nano-ZSM-5 catalysts with large amount and high strength of acid sites for conversion of methanol to hydrocarbons

Abstract Nano-ZSM-5 with large amount and high strength of acid sites were successfully synthesized by hydrothermal crystallization of pure-silica nucleus in NaAlO2 alkali solution. The concentration of NaAlO2 alkali solution was decreased by increasing the H2O/Al ratio from 200 to 2600, which strongly determined the acidic properties and crystal size of the obtained nano-ZSM-5. Low concentration of NaAlO2 alkali solution was found unfavorable for the incorporation of Al into the bulk of ZSM-5 crystal in crystallization process. Hence, more Al distributed at the exterior of crystals, which enhanced the accessibility of the acid sites during reaction. Large amount and high strength of acid sites were produced for nano-ZSM-5 by increasing H2O/Al ratio. When the H2O/Al ratio increased from 200 to 2600, the total amount of acid sites increased from 0.59 to 0.81 mmol g−1, much higher than conventional value of 0.50 mmol g−1. In addition, the acid strength increased and the ratio of Bronsted/Lewis acid sites were sharply increased from 2.3 to 4.1 when the H2O/Al ratio increased. Moreover, the size of nano-crystal was also decreased by above decreasing the concentration of the NaAlO2 alkali solution. When the H2O/Al ratio was 2600, the obtained sample possessed total acid amount of 0.81 mmol g−1 and crystal size of 60 nm, respectively. Methanol to hydrocarbon (MTH) reaction results showed that the increased acid sites of the catalyst decreased its catalytic lifetime to some extent, but the aromatics selectivity was tunable obviously. As for the catalyst prepared with H2O/Al ratio of 2000, the aromatics selectivity of the obtained catalyst reached to 66.0%. This paper provided a method for the fabrication of small-size nano-ZSM-5 with large amount and high strength of acid sites and regulated Al distribution for MTH reaction.

Relation of Catalytic Performance to the Aluminum Siting of Acidic Zeolites in the Conversion of Methanol to Olefins, Viewed via a Comparison between ZSM-5 and ZSM-11

ZSM-5 and ZSM-11 zeolites are similar in their crystalline framework structure, acidity, morphology, and textual properties but considerably different in their catalytic performance for conversion of methanol to olefins (MTO). Such an unexpected but exciting finding was extensively explored by various techniques and density functional theory calculations. A detailed investigation shows that it is the different Al distribution in the ZSM-5 and ZSM-11 framework that causes the significant difference in MTO catalytic performance. In ZSM-5, Al atoms are enriched in the intersection, whereas in ZSM-11, the Al atoms are concentrated in the straight 10-membered ring channel. The acid sites located in the intersection enhance the arene-based cycle that generates more ethene, alkanes, and aromatics. Nevertheless, these hydrocarbon molecules can easily diffuse out of the zeolite channel, hence retarding the deposition of carbonaceous materials and increasing catalytic stability. However, the acid sites located in t...

The Correlation Between the Preferred Orientation and Al Distribution of Al-Doped HfO2 Films by Plasma-Enhanced Atomic Layer Deposition

This research was mainly supported by the Global Frontier R&D Program (2013M3A6B1078874) on Center for Hybrid Interface Materials (HIM) funded by the Ministry of Science, ICT & Future Planning, Republic of Korea, and partially supported by the Future Semiconductor Device Technology Development Program (10067739) funded by Ministry of Trade, Industry & Energy (MOTIE) and Korea Semiconductor Research Consortium (KSRC), and this study has been conducted with the support of the Korea Institute of Industrial Technology development project (KITECH EO-18-0022). The first two authors (Da-Young Kim and Jaeho Jang) contributed equally to this paper.

Changes in the Elastic-Stress State and Phase Composition of TiAlN Coatings under Thermal Cycling

By means of XRD structural analysis and transmission electron microscopy, changes in the microstructure of TiAlN coatings deposited via magnetron sputtering after thermal cycling procedures (140 cycles) have been investigated. The thermal cycling procedure consisted in heating to 900°C and further cooling to room temperature. The sputtered target represented a 60 Ti–40 Al (at %) alloy. The coatings were deposited either onto a quenched austenitic steel substrate or onto the same substrate after preliminary Ti ion beam treatment. It is established that a layer of Ti and Al oxides with microcrystalline structure is formed on the coating surface in the course of thermal cycling. Compressive macrostresses under the oxide layer in the TiAlN coating decrease, whereas the heterogeneity of the Al distribution in the Ti1–хAl х N phase exhibits an increase. The preliminary Ti ion beam treatment of the substrate leads to an improvement of the coating thermal stability, to a decrease in the oxide layer thickness for the same number of thermal cycles, and to a wider Al concentration range in the Ti1–хAl х N phase of the surface coating layers.