Seed-assisted Method Research Articles

Preparation of High-Quality ZSM-22 Nanocrystals by the Seed-Assisted Method from Industrial Raw Materials

Preparation of High-Quality ZSM-22 Nanocrystals by the Seed-Assisted Method from Industrial Raw Materials

Alteration of acidity and porosity of Beta zeolite using fibrous silica for light olefin production

Traditional olefin production heavily depends on fossil fuels, which are a significant contributor to environmental issues. Methanol to olefin (MTO) is among non-fossil fuel alternatives to produce olefinic products from abundant resources, such as biomass, coal, and natural gas. Nevertheless, the catalytic reaction of MTO over commercial zeolite catalysts is hindered by their low activity, mainly due to the micropore structure and excessive acidity within the zeolite. Herein, Beta zeolite with fibrous silica structure was successfully synthesized via the microemulsion and Beta seed-assisted method. The catalysts were characterized using FESEM, N2 physisorption, and ammonia-TPD. FESEM results revealed a well-ordered spherical morphology of HFBETA with uniform particle size distribution. In surface analysis, the HFBETA exhibits higher BET surface area and mesopore volume compared to commercial HBETA by 35% and 86%, respectively. The introduction of fibrous silica within the Beta structure led to a significant drop in the acidity of the catalyst, as shown in ammonia-TPD results. These led to superior catalytic performance of HFBETA in the MTO process.

Evolution of Morphology, Fractal Dimensions, and Structure of (Titanium) Aluminosilicate Gel during Synthesis of Zeolites Y and Ti-Y

Zeolite Y and Ti-containing zeolite Y (1%, 2% and 5% TiO2) were synthesized by a hydrothermal seed-assisted method. In order to evidence the evolution of morphology, structure, and fractal dimensions during the zeolitization process at certain time intervals, a small volume from the reaction medium was isolated and frozen by lyophilization. The obtained samples were characterized by scanning electron microscopy (SEM), wide-angle X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). The fractal dimension values of the isolated samples, calculated from SAXS data, evidenced a transition from small particles with a smooth surface (2.021) to compact structures represented by zeolite crystallites with rough surfaces (2.498) and specific organization for zeolite Y. The formation of new structures during hydrothermal treatment, the increase in crystallite size and roughness due to the continuous growth were suggested by variation of fractal dimensions values, SEM microscopy images and X-ray diffractograms. The incorporation of titanium in low concentration into the zeolite Y framework led to the obtaining of low fractal dimensions of 2.034–2.275 (smooth surfaces and compact structures). On the other hand, higher titanium concentration (2%) led to an increase in fractal dimensions indicating structures with rougher surfaces and well-defined self-similarity properties. A mechanism for zeolite synthesis was proposed by correlation of the results obtained through morphological, structural, and fractal analysis.

Iron-Gold Nanoflowers: A Promising Tool for Multimodal Imaging and Hyperthermia Therapy.

The development of nanoplatforms prepared to perform both multimodal imaging and combined therapies in a single entity is a fast-growing field. These systems are able to improve diagnostic accuracy and therapy success. Multicomponent Nanoparticles (MCNPs), composed of iron oxide and gold, offer new opportunities for Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) diagnosis, as well as combined therapies based on Magnetic Hyperthermia (MH) and Photothermal Therapy (PT). In this work, we describe a new seed-assisted method for the synthesis of Au@Fe Nanoparticles (NPs) with a flower-like structure. For biomedical purposes, Au@Fe NPs were functionalized with a PEGylated ligand, leading to high colloidal stability. Moreover, the as-obtained Au@Fe-PEG NPs exhibited excellent features as both MRI and CT Contrast Agents (CAs), with high r2 relaxivity (60.5 mM−1⋅s−1) and X-ray attenuation properties (8.8 HU mM−1⋅HU). In addition, these nanoflowers presented considerable energy-to-heat conversion under both Alternating Magnetic Fields (AMFs) (∆T ≈ 2.5 °C) and Near-Infrared (NIR) light (∆T ≈ 17 °C). Finally, Au@Fe-PEG NPs exhibited very low cytotoxicity, confirming their potential for theranostics applications.

Seed-assisted synthesis of SAPO-34 zeolites: Genetic effect of seeds

BackgroundIn the past decades, seed-assisted synthesis of zeolites has become one of the research focuses. Understanding the effect of the seeds on their derived products, and thus tuning the physicochemical properties of those products by selecting suitable seeds is pivotal for synthesizing zeolites via seed-assisted method. MethodsIn this work, four kinds of SAPO-34 with different physicochemical properties were synthesized and used as seeds to prepare their corresponding products via the seed-assisted method. The physicochemical properties of the seeds and the corresponding products were characterized by XRD, SEM, N2 adsorption-desorption, NH3-TPD, and 29Si MAS NMR techniques. Significant FindingsThe results showed that the particle size, textural and acidity properties, and the silicon coordination of the seed-derived products are strongly correlated to their corresponding seeds, exhibiting genetic effects. By investigating the crystallization kinetics, we speculated that the genetic effects should be attributed to the incomplete dissolution of the seeds. During the crystallization process, the incompletely dissolved seed fragments are directly incorporated into the product and serve as models. These models then require the final zeolites to grow according to their patterns, retaining and inheriting their original characteristics.

Synthesis of Low Cost Titanium Silicalite-1 Zeolite for Highly Efficient Propylene Epoxidation.

Developing an effective and low-cost system to synthesize titanium silicalite-1 (TS-1) zeolite is desirable for a range of industrial applications. To date, the poor catalytic activity of the synthesized zeolite due to the low amount of framework titanium and large crystal size is the main obstacle limiting the widespread application of this material. Moreover, a large amount of wastewater is often produced by the existing synthesis process. Herein, a green and sustainable route for synthesizing small-crystal TS-1 with a high fraction of framework Ti was demonstrated via a seed-assisted method using a tetrapropylammonium bromide (TPABr)-ethanolamine hydrothermal system. The influence of the synthesis conditions on the physicochemical properties and catalytic activities of TS-1 was investigated. With the assistance of nanosized S-1 seeds, the incorporation of Ti into the framework of TS-1 was promoted, and the crystallization rate was effectively accelerated. After alkaline etching, the obtained hierarchical TS-1 had higher catalytic activity towards propylene epoxidation with an extremely high turnover frequency of 1,650 h−1. Furthermore, the mother liquid during the hydrothermal reaction could be reused for the next synthesis procedure. Consequently, utilization ratios of both ethanolamine and TPABr exceeding 95% were achieved by recycling the mother liquid. This low-cost approach for reducing wastewater could be easily scaled up to provide a promising synthesis method for the industrial production of TS-1 and other topological zeolites.

Realization of rapid synthesis of H-ZSM-5 zeolite by seed-assisted method for aromatization reactions of methanol or methane

H-ZSM-5 zeolites are successfully synthesized within 1 h with an organic template free system by the seed-assisted method. The synthetic method not only reduces the production cost of H-ZSM-5 zeolite, but also decreases the environmental pollution produced compared with that of the conventional synthesis process. Characterization by SEM, XRD, N2 adsorption–desorption, NH3-TPD, and Py-IR confirms that the H-ZSM-5 product has a high crystallinity and reveals that the rapid synthesis process is in accordance with the seed surface crystallization mechanism. To improve the aromatic selectivity on the H-ZSM-5 zeolite, different concentrations of Mo and Zn catalysts were prepared by incipient wetness impregnation and the ion-exchange method. Mo-Zn/H-ZSM-5-SAS-1 h have similar catalytic lifetimes and higher selectivity of paraxylene in aromatic products compared with Mo-Zn/H-ZSM-5-seed in the reaction of methanol to aromatic. However, the catalytic lifetime of 6%Mo/H-ZSM-5-SAS-1 h is shorter than that of the 6%Mo/H-ZSM-5-seed catalyst in methane to benzene reaction under the same reaction conditions.

Seeding-induced nano-sized SAPO-34 synthesis with superior MTO performance: Energy-efficient approach with highly reduced OSDA consumption

Methanol-to-olefin conversion is one of the most successful approaches to producing light olefins. It has been proved that SAPO-34 is the best catalyst for this process. This molecular-sieve is characterized by high thermal stability, moderate acid sites, and shape selectivity. In this report, SAPO-34 was synthesized using the seed-assisted method. Effects of OSDA and seed on crystallinity and particle size were investigated using Central Composite Design. Samples were characterized by XRD, FE-SEM, FTIR, BET, EDX, and TPD. Results showed that the samples had excellent physicochemical properties. The design of Experiments could predict the results accurately (R2 > 0.9). It was demonstrated that template was the key factor in the seed-assisted synthesis of SAPO-34. Template consumption was reduced by 50%, and it was proved that the synthesis time could be effectively decreased to 3 h due to rapid nucleation. Samples exhibited 100% methanol conversion and up to 90% selectivity toward ethylene and propylene.

Free-standing nitrogen-doped TiO2 nanorod arrays with enhanced capacitive capability for supercapacitors

TiO2 nanomaterials have attracted desirable attention as advanced electrode materials in supercapacitors, but they suffer from poor conductivity and low capacitance. Herein, we developed an effective approach to dramatically boost the capacitive capability of TiO2 nanorods by controlling the morphology of TiO2 and introducing N dopants upon nitridation process. The nitrided TiO2 with different morphologies are facilely synthesized by a seed-assisted hydrothermal method with different concentrations of nanosize TiO2 as seeds and subsequent nitridation. Without seeding, TiO2 nanorods are assembled into porous microflowers, while the introduction of seeds can induce the vertical growth of TiO2 nanorods. The results also show that the morphology of TiO2 can affect the doping degree of nitrogen. Owing to the improved charge transport and unique free-standing nanorod structure, the optimized nitrided TiO2 electrode obtains a remarkable areal capacitance of 177.1 mF cm−2 at 4 mA cm−2, which is much larger than nitrided TiO2 electrode without seeding (16 mF cm−2). This provides a general method for increasing the areal capacitance of nanomaterials by adjusting the seed solution concentration of the seed-assisted method.

Green synthesis route for MCM-49 zeolite using a seed-assisted method by virtue of an ultraphonic aging procedure

Highly crystallized MCM-49 zeolite can be obtained using the as-made MCM-49 as the seed without the addition of OSDA under mild conditions (140 °C, 30–38 h) with the aid of the ultraphonic aging procedure.

Synthesis of SAPO-34 with modifying Si distribution by seed-assisted method and its excellent catalytic performance for methanol to olefins

Low acidity SAPO-34 was synthesized by adding seeding SAPO-34 as Si source without additional Si reagent, named as CSSAPO-34-x (x = 1, 2, 3) according to the seeding SAPO-34 content for 6 wt%, 8 wt% and 9 wt%, respectively. The characterizations prove that the CSSAPO-34-x samples display much lower Si content and acidity, good catalytic performance and light olefins selectivity in methanol to olefins (MTO) process compared with the seeding SAPO-34 and the similar Si content SAPO-34 synthesized in one pot procedure. Further studies demonstrate that Si distribution can be manipulated when the seeding SAPO-34 is recrystallized by the hydrothermal treatment, decreasing the acidity of the CSSAPO-34-x, leading to much better catalytic MTO performance.

Synthesis of Submicron SSZ-13 with Tunable Acidity by the Seed-Assisted Method and Its Performance and Coking Behavior in the MTO Reaction.

Submicron SSZ-13 with different acidities was synthesized successfully with the assistance of nanosized SSZ-13 seeds. The methanol-to-olefins (MTO) properties of submicron SSZ-13 were evaluated. The lifetime of submicron SSZ-13 was enhanced because of the crystal size reduction. The selectivity of light olefins was improved evidently at the early stage of the MTO reaction as the acidity density decreased. TG, GC–MS, and in situ UV/vis spectra were utilized to investigate coking behavior during the MTO reaction. It was found that the acidity density influences the nature and rate of coke formation. The majority of the hydrocarbon pool species over SSZ-13 with a low acidity density (125.2 μmol/g) were methylated benzene carbocations, while that over SSZ-13 with a high acidity density (330.2 μmol/g) were methylated naphthalene carbocations. The low acidity density of SSZ-13 can suppress the hydrogen transfer reaction and polyaromatic generation.

Natural Aluminosilicate-based Y Zeolite for Catalytic Cracking of n-Hexadecane

Natural zeolite and kaolin are abundant in Indonesia especially in Java and Belitung islands. These materials generally contain high aluminosilicate minerals that can be used as silica and alumina sources for the formation of NaY zeolite. This research aimed to identify the modification of NaY zeolite structure using Bayat natural zeolite as alumina source and Belitung kaolin as silica source and its catalytic activity for n-hexadecane cracking. Pretreatment of materials were performed in several steps: activation, purification, fragmentation for Bayat–Klaten natural zeolite, and silica extraction for Belitung kaolin. The synthesis of NaY was performed hydrothermally using seed-assisted method with crystallization times of 24 and 48 h. The surface area analysis showed a typical surface area of microporous zeolite (i.e., a pore diameter of 1.897 nm) and surface area of 309.4 cm2/g. Meanwhile, powder X-ray diffraction characterization showed that the as-synthesized materials have the structure of NaY zeolite. The optimum crystallization time was 24 h with Si/Al ratio of 4.10. Furthermore, both synthetic and natural sourced NaY zeolites were converted into HY zeolites and employed as cracking catalyst of n-hexadecane in a fixed-bed reactor at 500 °C for 75 s. The natural sourced HY resulted in 59.80% conversion and 59.80% yield of gasoline product (C9–C12). These values were lower than the results given by synthetic HY (80%).

In-situ synthesis of hierarchical lamellar ZSM-5 zeolite with enhanced MTP catalytic performance by a facile seed-assisted method

A seed-assisted route has been applied to prepare the hierarchical lamellar ZSM-5 zeolite with good porosity and catalytic performance in methanol to propylene (MTP) reaction. In this method, ZSM-5 crystal seeds instead of organic quaternary ammonium were used to direct the formation of ZSM-5 nuclei and conventional surfactant cetyltrimethylammonium bromide (CTAB) employed as the mesoporogen. The process for the formation of hierarchical lamellar ZSM-5, including the effect of the ratio of CTAB/SiO2, initial gel aging temperature, synthesis temperature and synthesis time were discussed in detail. The results suggested that mesoporous structure was first obtained and then transformed into MFI structure in-situ during the hydrothermal synthesis process. The obtained hierarchical lamellar ZSM-5 zeolite displays an organized flack-like nanosheet stacks morphology with regular intercrystal mesopores of 3–7 nm, possessing large surface area and mesopore volume. Moreover, the synthesized hierarchical ZSM-5 zeolite has perfect catalyst lifetime in methanol to propylene (MTP) reaction than conventional microporous ZSM-5 zeolite, which could be ascribed to the hierarchical mesoporous structure accommodating more bulky molecules and accessible acid sites in the catalytic reaction.

Revisiting the seed-assisted synthesis of zeolites without organic structure-directing agents: insights from the CHA case.

Herein, the crystallization behaviour of the CHA zeolite synthesized via the seed-assisted method and in the absence of an organic structure-directing agent has been revisited. To date, the working hypothesis of the seed-assisted synthesis method is that the parent gel and seed share the common composite building unit (cbu) of the targeted zeolite crystal. In the case of the CHA zeolite, we reveal that the parent gel in the absence of CHA seeds leads to the formation of the MER zeolite, which does not follow the cbu working hypothesis. It appears that smaller, but essential common units, i.e., 4-membered ring (4-MR) aluminosilicate, play a key role, instead of a larger cbu. The parent gel contains 4-MRs, which can grow into MER and/or CHA, depending on several factors, i.e. alkalinity, Si/Al ratio, synergistic effects of Na+ and K+, and the seeds. In this study, the CHA zeolite with an Si/Al ratio of up to 15 was selectively crystallized in the presence of CHA seeds at suitable alkalinity ((Na2O + K2O)/SiO2 < 0.4) with a fixed point at the tie line of Na2O/SiO2 = 0.3 with K2O/SiO2 = 0.1. Subsequently, the ternary phase diagram was drawn as high alkalinity with (Na2O + K2O)/H2O > 0.4 showing the formation of an MER zeolite, a thermodynamically more stable phase than the CHA zeolite, whereas low alkalinity with (Na2O + K2O)/SiO2 < 0.4 showed the less crystalline CHA zeolite or amorphous products with MER as a competing phase. The crystallization of the CHA zeolite was found to be strongly dependent on the synergistic effects of sodium and potassium ions. The former appears to organize the 4-MRs into essential double-six rings (d6rs), while the latter arranges the formed d6rs into cha cages. The seeds are partially dissolved and provide the outer surface for the crystal growth of CHA. We anticipate that these results may provide useful insight for understanding the crystallization of zeolites and stimulate versatile design in the synthesis of zeolites, particularly for the industrially demanding seed-assisted technique.

Seed-Assisted Synthesis and Catalytic Performance of Nano-sized ZSM-5 Aggregates in a One-Step Crystallization Process

Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide (CTAB) through a facile one-step crystallization process. Commercial ZSM-5 zeolites with a SiO2/Al2O3 ratio comparable to that of ZSM-5 products were treated with alkali and used as the seed particles. The influences of crystallization conditions were investigated, and the possible synthesis mechanism was proposed. ZSM-5 zeolites with different amounts of CTAB added were characterized using many techniques and evaluated in toluene alkylation with methanol. The results showed that a trace amount of CTAB significantly promoted the crystallization of ZSM-5 zeolite, with the morphology changing from hexagonal-shape crystals to uniform spherical aggregates. CTAB may act as the structure-directing agent and assemble the primary crystallites to generate hierarchical ZSM-5 aggregates. The ZSM-5 zeolite with the smallest primary particles of 50–80 nm exhibited large specific surface area, abundant mesopores, and the greatest microporosity. The hierarchical nano-sized ZSM-5 aggregate showed higher toluene conversion and a longer lifetime without compromising the selectivity to xylene and p-xylene in toluene alkylation with methanol.

Synthesis of Submicron-Sized SAPO-34 as Efficient Catalyst for Olefin Generation from CH3Br

Submicron-sized SAPO-34 zeolites were synthesized via nanosheet seed-assisted method using cheap diethylamine as the template. Only 2 wt % seeds are needed to obtain the submicron-sized SAPO-34 (ca. 700 nm). Further increase of seed dosage has little effect on reducing the crystal size but leads to an increase of acidity. Among the as-prepared samples, S-0.3-2% (SiO2/Al2O3 = 0.3, 2 wt % seed) shows the best catalytic performance (CH3Br conversion of up to 95%, ethylene and propylene selectivity of 94%, and a lifetime of over 125 min) ever reported in the studies of CH3Br conversion to light olefins. The results undoubtedly demonstrate that lifetime and olefin selectivity are highly dependent on the particle size and acidity of SAPO-34 zeolites. The decrease of particle size and acidity is beneficial to alleviating carbon deposition, resulting in enhanced catalyst lifetime. In addition, the decrease of particle size and lowering of acidity could diminish the second hydrogen transformation reactions of olef...

Hierarchical Ti-containing hollownest-structured zeolite synthesized by seed-assisted method for catalytic epoxidation of alkenes efficiently

Recently, a Ti-containing hollownest-structured zeolite (Ti-HSZ) material with the shell constructed by randomly intergrown MWW (framework type code) flaky crystals has been synthesized through one-step rotating hydrothermal method within 3.5 days, which shows predominant catalytic property for the epoxidation of alkenes. Herein, it is firstly reported that the crystallization efficiency of Ti-HSZ material can be notably increased by applying seeds-assisted synthesis method. Thus-crystallized materials have been characterized by XRD, UV–vis, XPS, SEM, TEM, FT-IR, and N2 adsorption-desorption. Moreover, the key controlling factors are revealed to include the addition percentage of seed crystals, rotating rate and filling degree of autoclave. When 2 wt% or 3 wt% seed crystals are added into the reaction gel, the crystallization time of Ti-HSZ can be sharply reduced to 2.5 days or even 2.0 days, respectively. Particularly, thus-synthesized Ti-HSZ-SM material still maintains hollownest morphology characteristic and excellent catalytic activity and catalytic stability. About 95% allyl chloride can be converted into corresponding epoxide when using H2O2 as oxidant, and about 85% cyclopentene and 87% cyclooctene can be converted into corresponding epoxides when using TBHP as oxidant, with the selectivity for epoxides of nearly 100%.

Exploring the synthesis conditions to control the morphology of gold-iron oxide heterostructures

Gold–iron oxide nano-heterostructures with a clear and well-defined morphology were prepared via a seed-assisted method. The synthesis process and the events of heterogeneous nucleation during the decomposition of the iron precursor were carefully studied in order to understand the mechanism of the reaction and to tailor the architecture of the fabricated heterostructures. When employing Au seeds of 3 and 5 nm, nanoparticles with a dimer-like morphology were produced due to the occurrence of a single iron oxide nucleation event. Otherwise, multi-nucleation events could be favored by two mechanisms: (i) by the incorporation of a reducing agent and the slowing down of the heating protocol, leading to a core–shell system; (ii) by the increase of the Au seed size to 8 nm, leading to a flower-like system. Further increase of the Au seed size to 12 nm using similar synthesis conditions promotes the homogeneous nucleation and growth of the iron oxide phase, without formation of heterostructures. An in-depth study was performed on the gold–iron oxide heterostructures to confirm the epitaxial growth of the oxide domain over the Au seed and to analyze the elemental distribution of the components within the heterostructures. Finally, it was found that the modification of the plasmonic properties of the Au nanoparticles are strongly influenced by the architecture of the heterostructure, with a more pronounced damping effect for the systems produced after multi-nucleation events.

Oxidative desulfurization of dibenzothiophenes over metallic and bimetallic supported ZSM-11 catalysts: xLa/yMo-ZSM-11 as an efficient bimetallic catalyst

In the present work, ZSM-11 zeolite was synthesized using the seed-assisted method and the proposed template of N,N-diethylaniline was used as a structure directing agent. Synthesized zeolite was characterized by FT-IR, XRD, FE-SEM and BET analysis. Oxide of intermediate metals of molybdenum, vanadium, lanthanum, cobalt, copper, and cerium was stabilized in the zeolite. The zeolite base catalysts applied as heterogeneous catalyst in the oxidative desulfurization (ODS) process for the model fuel including n-heptane, dibenzothiophene (DBT) with hydrogen peroxide as oxidant and ethanol as extractive solvent. The highest conversion percent of dibenzothiophene belongs to molybdenum, vanadium, and lanthanum. Different molar percentage of molybdenum and lanthanum were stabilized in zeolite and the yield of conversion of their dibenzothiophene to each other was compared. Finally, through the GC–MS reported data, dibenzothiophene sulfone and sulfur removal mechanism were identified. The results showed that the conversions of dibenzothiophene to dibenzothiophene sulfone achieve 100% under optimal experimental conditions.