An investigation of the crystallization kinetics of zeotype SAPO-34 crystals synthesized by hydrothermal and sonochemical methods

Synthesis and Crystallization Mechanism for SAPO-34 Zeolite Derived from Magadiite

In this work, we explored the hydrothermal synthesize and crystallization process of SAPO-34 zeolites from two-dimensional layered silicate magadiite by using tetraethylammonium hydroxide (TEAOH) as a templating agent. Comprehensive characterization was conducted by XRD, SEM, FTIR, Raman, and BET. Time-resolved PXRD analysis revealed that SAPO-34 zeolite exhibited a steep growth curve when the crystallization time was 30 h, and the crystallinity reached 98.65 % at 48 h. Specifically, the disruption of the magadiite layer exposed charged silanol groups on the surface, fostering an affinity for AlO4 and PO4 species, thereby initiating the nucleation process. Under the guidance of TEAOH, these nucleation sites transformed into SAPO-34 nuclei, gradually advancing towards crystallization. FTIR and Raman analyses affirmed the presence of 6Rs, followed by D6R and 4Rs SBUs, along with the characteristic CHA structure. Combined with 29 Si NMR established that disaggregated silicate minerals served as zeolite synthesis "seeds", enhancing nucleation sites and overall crystallization efficiency.

Amphipathic Solvent-Assisted Synthetic Strategy for Random Lamellae of the Clinoptilolites with Flower-like Morphology and Thinner Nanosheet for Adsorption and Separation of CO2 and CH4

The random lamellae of the synthetic CP were synthesized with a hydrothermal approach using o-Phenylenediamine (OPD) as a modifier. The decreases in the order degree of the CP synthesized in the presence of the OPD resulted from the loss of long-range order in a certain direction. Subsequently, the ultrasonic treatment and washing were conducive to further facilitate the disordered arrangements of its lamellae. The possible promotion mechanism regarding the nucleation and growth behaviors of the sol-gel particles was proposed. The fractal evolutions of the aluminosilicate species with crystallization time implied that the aluminosilicate species became gradually smooth to rough during the crystallization procedures since the amorphous structures transformed into flower-like morphologies. Their gas adsorption and separation performances indicated that the adsorption capacity of CO₂ at 273 K reached up to 2.14 mmol·g^-1 at 1 bar, and the selective factor (CO₂/CH₄) up to 3.4, much higher than that of the CPs synthesized without additive OPD. The breakthrough experiments displayed a longer breakthrough time and enhancement of CO₂ uptake, showing better performance for CO₂/CH₄ separation. The cycling test further highlighted their efficiency for CO₂/CH₄ separation.

Constructing Randomly Lamellar HKUST-1@Clinoptilolite through Polyethylene Glycol-Assisted Hydrothermal Method and Coordinated Complexation for Enhanced Adsorptive Separation for CO2 and CH4

Clinoptilolite (CP) was successfully synthesized via a hydrothermal route in the presence of polyethylene glycol (PEG), and it was then delaminated by washing using Zn²⁺ containing acid. HKUST-1, as one kind of the Cu-based MOFs, showed a high CO₂ adsorption capacity owing to its large pore volume and specific surface area. In the present work, we selected one of the most efficient ways for preparing the HKUST-1@CP compounds via coordination between exchanged Cu²⁺ and ligand (trimesic acid). Their structural and textural properties were characterized by XRD, SAXS, N₂ sorption isotherms, SEM, and TG-DSC profiles. Particularly, the effect of the additive PEG (average molecular weight of 600) on the induction (nucleation) periods and growth behaviors were detailed and investigated in the hydrothermal crystallization procedures of synthetic CPs. The corresponding activation energies of induction (E_n) and growth (E_g) periods during crystallization intervals were calculated. Meanwhile, the pore size of the inter-particles of HKUST-1@CP was 14.16 nm, and the BET specific area and pore volume were 55.2 m²/g and 0.20 cm³/g, respectively. Their CO₂ and CH₄ adsorption capacities and selectivity were preliminarily explored, showing 0.93 mmol/g for HKUST-1@CP at 298 K with the highest selective factor of 5.87 for CO₂/CH₄, and the dynamic separation performance was evaluated in column breakthrough experiments. These results suggested an efficient way of preparing zeolites and MOFs composites that is conducive to being a promising adsorbent for applications in gas separation.

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.

A nanoprecursor method for successfully synthesizing clinoptilolite with high-crystallinity and resultant effects on CO2/CH4 selective adsorption

Nanoprecursors used as a structural promoter (SP) were prepared by a hydrothermal method and named sol-SP. After centrifugation, the supernatant and precipitate were denoted as solution-SP and solid-SP, respectively. The effect of the additive amount on the structures and properties of the synthesized clinoptilolite was investigated using various characterization techniques. The activation energies of crystallization kinetics during induction and growth periods were calculated. The results showed that the induction period is the control step during the synthesis of clinoptilolite, while additive sol-SP or solid-SP was beneficial to shorten the induction period and therefore enhance the formation of the crystal nucleus. When their pre-crystallization time was too long or the additive amount was too much, the impure phase (phillipsite) in the synthesized clinoptilolite was easily generated. Although the addition of solution-SP had no obvious effect on the induction period, it promoted the growth of crystals after nucleation. Finally, the adsorption performances for CO₂ and CH₄ were preliminarily assessed using synthetic clinoptilolite as the adsorbent, showing the promising application for the separation of CO₂/CH₄.

Nanoprecursors used as a structural promoter (SP) were prepared by a hydrothermal method and named sol-SP.

Promoted crystallization of silicoaluminophosphate zeolites: an efficient way to accelerate crystallization rate and increase solid yield

SAPO-34 with 100% yield has been synthesized by an acid-assisted method, which is also applicable to the synthesis of other silicoaluminophosphate zeolites.

Performance analysis of ultrasound-assisted synthesized nano-hierarchical SAPO-34 catalyst in the methanol-to-lights-olefins process via artificial intelligence methods

The present study has focused on performance analysis of ultrasound-assisted synthesized nano-hierarchical silico-alumino-phosphate-34 (SAPO-34) catalyst during methanol-to-light-olefins (MTO) process. A classical method, i.e., multiple linear regression (MLR) and two intelligent methods, i.e., genetic programming (GP) and artificial neural networks (ANN) were used for modeling of the performance of nano-hierarchical SAPO-34 catalyst. We studied the influence of basic parameters for the sonochemical synthesis of nano-hierarchical SAPO-34 catalyst such as crystallization time, ultrasonic irradiation time, ultrasonic intensity, amount of organic template (diethylamine (DEA) and carbon nanotube (CNT)) on its performance (methanol conversion and light olefins selectivity) in MTO process. The results revealed that the models achieved using the GP method had the highest accuracy for training and test data. Therefore, GP models were used in the following to predict the effect of main parameters for the sonochemical synthesis of nano-hierarchical SAPO-34 catalyst. Finally, an optimal catalyst with the highest yield into light olefins was predicted using the genetic optimization algorithm. The genetic models were employed as an evaluation function in the genetic algorithm (GA). A good agreement between the outputs of GP models for the optimal catalyst and experimental results were obtained. The optimal ultrasound-assisted synthesized nano-hierarchical SAPO-34 was accompanied by light olefins selectivity of 77% and methanol conversion of 94% from the onset of the process after 9 h.

Presenting a new kinetic model for methanol to light olefins reactions over a hierarchical SAPO-34 catalyst using the Langmuir-Hinshelwood-Hougen-Watson mechanism

In this study, a new kinetic model for methanol to light olefins (MTO) reactions over a hierarchical SAPO-34 catalyst using the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism was presented and the kinetic parameters was obtained using a genetic algorithm (GA) and genetic programming (GP). Several kinetic models for the MTO reactions have been presented. However, due to the complexity of the reactions, most reactions are considered lumped and elementary, which cannot be deemed a completely accurate kinetic model of the process. Therefore, in this study, the LHHW mechanism is presented as kinetic models of MTO reactions. Because of the non-linearity of the kinetic models and existence of many local optimal points, evolutionary algorithms (GA and GP) are used in this study to estimate the kinetic parameters in the rate equations. Via the simultaneous connection of the code related to modelling the reactor and the GA and GP codes in the MATLAB R2013a software, optimization of the kinetic models parameters was performed such that the least difference between the results from the kinetic models and experiential results was obtained and the best kinetic parameters of MTO process reactions were achieved. A comparison of the results from the model with experiential results showed that the present model possesses good accuracy.

Improving the visible light photoelectrochemical activity of synthesized TiO2nanotube arrays in an organic electrolyte containing sodium carbonate with doping by copper via single-step anodization

The main aim of this research is to improve the photocatalytic activity of TiO₂nanotubes by co-doping with copper and sodium for application in the water splitting process as a photoanode.

Physicochemical characterization to assess Ni and Zn incorporation into zeotype SAPO-34 nanoparticles synthesized with different mixing methods through ultrasound-promoted crystallization

The effect of synthesis parameters on the properties of Ni- and Zn-containing SAPO-34 nanoparticles prepared by applying insonation was investigated to elucidate how the isomorphous substitution of metal ions was influenced by synthesis conditions.