The arrangement of Al heteroatoms in zeolite frameworks influences turnover rates of Brønsted acid-catalyzed reactions and the speciation of exchanged metal cations and complexes that are active sites for redox catalysis. The substitution of Al for Si in zeolite frameworks generates anionic lattice charges and is thus influenced by the structure and charge density of the cationic structure directing agents (SDAs) that guide zeolite crystallization. Here, we investigate how framework Al structure and arrangements in chabazite (CHA) zeolites evolve as a function of hydrothermal treatment time as amorphous Al and Si precursors convert into partially and fully crystalline aluminosilicate phases in the presence of organic and inorganic SDAs. With N,N,N-trimethyl-1-adamantylammonium (TMAda + ) as the sole SDA, an amorphous aluminosilicate network initially forms that contains a large fraction of proximal Al sites, as quantified by Co 2+ titration, which evolves into CHA crystallites that contain a high fraction of proximal Al sites in six-membered rings (6-MR). After bulk crystallization has been completed (433 K, 36 h), continued hydrothermal treatment causes rearrangement of framework Al to become more site-isolated, eventually resulting in CHA crystallites with undetectable numbers of 6-MR paired Al sites (433 K, 144 h). These temporal changes in framework Al arrangement indicate that Si−O−Al linkages remain labile and undergo restructuring within crystalline domains under hydrothermal conditions, allowing for atomic rearrangement toward thermodynamically preferred framework Al distributions (e.g., 6-MR isolated Al sites in the presence of TMAda + only). Ab initio molecular dynamics (AIMD) simulations report isolated Al configurations to be lower in energy than 6-MR Al pair configurations in a field of TMAda + , supporting a thermodynamic driving force for Al sites to isolate when TMAda + is the sole SDA. In contrast, using both Na + and TMAda + as inorganic and organic co-SDAs did not result in any further changes to the framework Al arrangement after CHA crystallization was complete (433 K, 96 h), suggesting that the co-occlusion of Na + and TMAda + suppresses the lability of framework Si−O−Al bonds and Al rearrangement in crystalline phases. AIMD simulations report 6-MR paired Al sites to become lower in energy than isolated Al configurations when charge-balanced by both Na + and TMAda + . These findings indicate that Al arrangements in zeolite frameworks can evolve upon extended hydrothermal treatment after bulk crystallization has been completed from amorphous Si and Al precursors and that such evolution is influenced by thermodynamic factors, extending prior reports of such phenomena occurring during interzeolite conversion routes.
Introduction: Irreversible electroporation (IRE) combined with a catheter-based electrode during endoscopy is a potential alternative treatment method for digestive tract tumors. The aim of this study was to investigate the electrical injury (EI) and thermal injury (TI) to the digestive tract via numerical analyses and to evaluate the role and impact of electrode configurations and pulse settings on the efficacy and outcomes of IRE. Materials and methods: A finite element method was used to solve the numerical model. A digestive tract model having 4-mm-thick walls and two catheter-based electrode configuration models were constructed. The distributions of electric fields, temperature, electrical conductivity, tissue injury and limitation on the pulse number required for IRE were calculated and compared. Results: Electrode length is an important geometric parameter for electrodes in the monopolar model (MPM), while electrode spacing affects the outcomes in the bipolar model (BPM). Increasing the pulse voltage reduces the pulse number required for tissue ablation, while increasing the risk of TI. In total, there were 6 NT-IRE protocols, 12 thermal-IRE protocols and 30 TI protocols. All of the NT-IRE protocols were set in BPMs with a voltage of 0.50 kV. With increasing electrode spacing, the minimum pulse number decreased. However, thermal effects were inevitable in the MPM. Conclusions: The electrode configuration and pulse settings are adjusted to achieve NT-IRE synergistically. The BPM is more reliable for achieving NT-IRE in 4-mm-thick digestive wall. Future in vitro and in vivo studies are needed to support and validate this conclusion.
ARTICLE HISTORY
To make ionic liquids (ILs) accessible and economical, ethylene glycol was mixed in 1-ethyl-3-methylimidazolium-dicyanamide ([EMIm]DCA) to obtain droplets that could experimentally collide white fuming nitric acid. To investigate the ignition delay (ID) time theoretically in terms of hydrodynamics, alcohol fuels and kerosene were used as combustibles, while the intermiscibility between them and nitric acid (HNO 3 ) was calculated using the ternary phase-field method alongside finite element analysis. The specific impulses of blend fuels were calculated by a thermodynamic method and compared to ILs. When the droplet was ethylene glycol/ [EMIm]DCA with a 2.1 mm diameter and a 1.69 m/s colliding velocity, the ID time was the shortest. Kerosene was not an applicable additive for [EMIm]DCA owing to its lower intermiscibility with ILs and HNO 3 than alcohol fuels; alcohol fuels, however, were appropriate. The concentration of ethylene glycol in the oxidizer pool increased faster than the concentration of propylene glycol, triggering more rapid hypergolic ignition in the first 50 ms. The protocols regarding the hypergolic ignition conditions were verified, i.e., the size of the droplet had to be minute when the colliding velocity was as fast as possible; this was carefully calculated using ethylene glycol. According to thermodynamic calculations, the addition of alcohol fuels can improve the specific impulse of fuels, with ethylene glycol performing the best. The feasibility of adding alcohol fuels to ILs was confirmed via experiments and thermodynamic computations, with the simulation results providing some guidance on selecting the experimental or engineering conditions or both.
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