Seed-induced Method Research Articles

ZnFe-LDH synthesized by seed-induced method to simultaneous enhance arsenic removal, stabilization and sludge reduction

To simultaneously enhance arsenic removal, stabilization and sludge reduction, a seed-induced method was applied to in-stiu synthesize ZnFe-LDH containing arsenic (ZnFe-As-LDH). The optimal seed was determined to be ZnFe-LDH by analyzing the effects of the unseeded system and seed-induced system (FeⅡFeⅢ-LDH, ferrihydrite and ZnFe-LDH). In the ZnFe-LDH seed system, the arsenic removal efficiency increased and the arsenic leaching concentration were drastically reduced by 91.33% under the optimal conditions as the seeds dosage of 2.5g/L, pH 10 and Zn/Fe ratio of 1.5. The addition of seed crystals promoted crystal growth and aggregation and finally regulated the formation of dense bulk LDH with fewer pores and smaller pore sizes. The arsenic removal and stabilization were achieved by converting active arsenic into more stable crystalline bound arsenic through coprecipitation, ion exchange and complexation. The SV30 was reduced by 73.68% and it was due to reduction of unstable surface water and interspace and crystallinity enhancement. The formation pathway of ZnFe-As-LDH by seed-induced was elucidated. The seed-induced method promoted the formation of arsenic-containing ferrihydrite and Zn(OH)2 coprecipitations on the surface of ZnFe-LDH seed, and led to a structural rearrangement to generate ZnFe-As-LDH.

Catalytic upgradation of crude glycerol to produce bio-based aromatics over hierarchical MFI zeolite: Effect of bimodal hierarchical porosity enhancement and porosity-acidity interaction

The transformation of renewable biomass derived crude glycerol into value-added BTX aromatics is an attractive approach to facilitate carbon neutrality and recycling economy. Herein, two kinds of hierarchical HZSM-5 with distinct hierarchical porosity and acidity distribution were synthesized based on a seed-induced method by utilizing CTAB and TPOAC as soft mesoporogens, respectively. And the effects of bimodal hierarchical porosity and porosity-acidity interaction on the upgradation efficiency during the conversion of crude glycerol over hierarchical HZSM-5 were investigated. The abundant intra-mesopores and promoted porosity-acidity interaction in hierarchical HZSM-5 facilitated the transformation of macromolecules in crude glycerol into small oxygenated chemicals and olefins, resulting in higher BTX yield and longer catalyst lifetime. Among all catalysts, the hierarchical HZSM-5 sample templated with TPOAC exhibited the maximum carbon yields of BTX (38.5%) and longest lifetime (23 h) due to the better interconnectivity of shape-selective micropores and high mass transfer intra-mesopores. The reaction route and product distribution of upgradation of crude glycerol was strongly dependent on the morphology, bimodal hierarchical porosity and acidity variation resulting from the generation of intra-mesopores in HZSM-5 catalysts by the usage of different soft mesoporogens. The liquid route and side alkylation reaction was accelerated over HZSM-5/TPOAC catalyst while the gas route and secondary coking reaction was promoted over HZSM-5/CTAB sample.

Rapid and low-cost synthesis of ZSM-5 zeolite nanosheet assemblies for conversion of methanol to gasoline

Nanoscale zeolites with short diffusion paths show significantly enhanced mass transportation and easier accessibility for active sites in catalysis compared to microsized zeolites. However, the high cost and complex process involved in existing synthetic methods limit their application, so the development of a rapid and low-cost synthesis technology is of great significance. Herein, ZSM-5 zeolite nanosheet assemblies (Z5-NS-t) are rapidly synthesized by a microwave irradiation (MW) assisted seed-induced method using low-cost polyhexamethylene biguanide hydrochloride (PHMB) as a crystal growth inhibitor of the b-axis. The crystallization kinetics of the resultant materials and the formation mechanism of ZSM-5 zeolite nanosheets, as well as the influence of physico-chemical properties on their catalytic performance for the methanol-to-gasoline (MTG) reaction, are systematically investigated. Compared with the ZSM-5 nanoparticle assemblies (Z5-NP-60), which are synthesized by using the same method except for the addition of PHMB, Z5-NS-180 nanosheets with an approximate density of strong Brønsted acid sites exhibit excellent catalytic performance in the MTG reaction, giving rise to a high gasoline selectivity of 73.2% at a methanol conversion of 99.9% and a large amount of external carbon deposits. This is attributed to the synergy of accessibility of acid sites located in the pore intersections and the shorter diffusion paths for coke precursors out of the zeolite channel. This study provides an effective strategy for the synthesis of ZSM-5 nanosheets as catalysts for the MTG reaction, and it is expected to be applied for the synthesis of other zeolite nanosheets for important catalytic processes.

Liquid deposition modification of nano-ZSM-5 zeolite and catalytic performance in aromatization of Hexene-1

The Olefin aromatization is an important method for the upgrade of catalytic cracking (FCC) gasoline and production of fuel oil with high octane number. The nano-ZSM-5 zeolite was synthesized via a seed-induced method, a series of modified nano-ZSM-5 zeolite samples with different Ga deposition amount were prepared by Ga liquid deposition method. The XRD, N2 physical adsorption, SEM, TEM, XPS, H2-TPR and Py-IR measurements were used to characterize the morphology, textural properties and acidity of the modified ZSM-5 zeolites. The catalytic performance of the Hexene-1 aromatization was evaluated on a fixed-bed microreactor. The effects of Ga modification on the physicochemical and catalytic performance of nano-ZSM-5 zeolites were investigated. The Ga species in the modified nano-ZSM-5 zeolites mainly exist as the form of Ga2O3 and GaO+, which provide strong Lewis acid sites. The aromatics selectivity over Ga modified nano-ZSM-5 zeolite in the Hexene-1 aromatization was significantly increased, which could be attributed to the improvement of the dehydrogenation activity. The selectivity for aromatics over the Ga4.2/NZ5 catalyst with suitable Ga deposition amount reached 55.4%.

Improvement in Electrical Properties of (Bi0.5Na0.5)TiO3 (BNT) Ceramics Using the Seed-Induced Method

(Bi0.5Na0.5)TiO3 (BNT) lead-free ceramics were prepared by the seed-induced technique using different particle sizes of BaTiO3 (BT) powder as seeds. The BT seeds was synthesized by the molten-salt method and then calcined at different temperatures of 750 (750BTs), 800 (800BTs) and 850 °C (850BTs). The pure perovskite seeds (5 mol%) were mixed with the starting materials of the BNT system for conventional mixed oxide method. After that, the mixture was calcined and sintered at 900 °C for 2 h and 1100 °C for 2 h, respectively. From results it was found that the particle size of BT seed increased with calcine temperature increase from 750 to 850 C. The samples of non-BT seed (S0) and BT seed-added (S1, S2 and S3) showed pure perovskite phase. Average density values were in the range of 5.53-5.77 g/cm3. Dielectric constant (εr) measured at room temperature (at 1 kHz) was in the range of 732.04-788.59. The dielectric loss (tanδ), remnant polarization (Pr) and coercive field (Ec) values decreased with the addition of BT seed. The highest piezoelectric coefficient (d33) ∼156 pC/N was obtained for the sample of 850BTs (S3).

In-situ microwave synthesis of nano-GaZSM-5 bifunctional catalysts with controllable location of active GaO+ species for olefins aromatization

Abstract Sustainable development of clean fuels demands a less energy-consuming procedure for the rapid synthesis of high-efficiency catalysts applied in the aromatization of olefins. Here, nanosized ZSM-5 aluminosilicates and GaZSM-5 gallosilicates catalysts were prepared via a seed-induced method by using conventional electric (CE) heating and microwave radiation (MW) heating. The effects of the heating strategy on the morphology, textural property and acidity of the synthesized samples, and also their catalytic performance of 1-hexene aromatization were studied. The results showed that the synergy of Bronsted acid site (BAS) and Lewis acid sites (LAS) provided by active GaO+ species in the catalysts played an important role in 1-hexene aromatization. MW heating can effectively promote the formation of well-dispersed GaO+ species located in the zeolite channels in proximity to BAS, providing higher dehydrogenation activity. Due to the closer spatial proximity and improved synergic effect between BAS and active GaO+ species, the nanosized GaNZ5-MW/MW sample prepared by two-step MW heating in both seed preparation and crystallization exhibited the highest BTX selectivity and the lowest coke-burning activation energy.

Modified seeding method to produce hierarchical nanocrystalline ZSM-5 zeolite

A series of ZSM-5 nano-zeolites with hierarchical porosity was prepared by a modified seed-induced method using a mixture of silicate-1 and commercial Na-ZSM-5 zeolite as a seed to reduce the production cost. The XRD and FTIR results proved that the pure ZSM-5 phase with a high degree of crystallinity was crystallized. Furthermore, the synthesized samples using a mixture of silicate-1 and commercial ZSM-5 as a seed exhibited more dealumination during the hydrothermal aging process, resulting in a higher Smeso/SBET ratio than other samples and the highest ratio of Brönsted/Lewis acid sites among all the samples. The SEM and BET results also confirmed that the final pH after the synthetic process extensively affected the morphology, specific area and pore volume of products. The purposed method by employing a lower amount of the organic template and silica source might lead to a more economical and environmentally friendly approach for the hierarchical ZSM-5 zeolite production to benefit the relevant industries.

Seed-induced synthesis of functional MFI zeolite materials: Method development, crystallization mechanisms, and catalytic properties

As an important zeolite material, MFI zeolites, as well as their controllable synthesis, are of great interest in both basic and applied science. Among the developed synthetic approaches, the seed-induced method has gradually evolved into a facile, low-cost, and even green alternative to give zeolites the desirable physicochemical properties. In this review, we briefly summarize the development of seed-induced syntheses of diverse functional MFI zeolites, where the “living” seed crystals not only direct the formation of zeolitic framework but also function as special “templates” or “units” to fine-tune the zeolite materials with diverse sizes, shapes, compositions, morphologies and pore structures. Moreover, on the basis of their structural features and crystallization behaviors in seed-induced synthesis, we reveal the roles of seeds and discuss the related crystallization mechanisms including both classical and non-classical pathways. We also want to guide readers to investigate the structure-performance relationships between these functional MFI zeolite catalysts and suitable catalytic reactions.

High-efficiency nano [Zn,Al]ZSM-5 bifunctional catalysts for dimethyl ether conversion to isoparaffin-rich gasoline

The development of nonpetroleum routes for producing high-octane clean gasoline rich in isoparaffins is still an important challenge today. Here, nanosized ZSM-5 (NZ5) and zinc isomorphously substituted ZSM-5 ([Zn,Al]NZ5) zeolites with different Si/Me ratios in initial gels (Me = Al or Al and Zn) were prepared in situ by a seed-induced method and were used as high-efficiency catalysts in the reaction of dimethyl ether (DME) to gasoline (DTG). It was found that the formation of isoparaffins and aromatics are competitive processes. The long-chain olefin intermediates can be converted to aromatics by cyclization and hydrogen transfer on the Brønsted acid site (BAS), whereas they undergo the hydroisomerization to form isoparaffins on the hydrogenation species. Excellent catalytic activity and high isoparaffin selectivity were obtained for the [Zn,Al]NZ5 samples due to the reduced BAS and the unique ZnOH+ species with high ability for the heterolysis of hydrogen and hydrogenation activity under a syngas atmosphere. When the reaction atmosphere changes from syngas to H2, the isoparaffin selectivity in gasoline component over the [Zn,Al]NZ5(20) sample increased further, from 67.3 wt% to 76.5 wt%, which is superior to the NZ5 series of samples and to ever reported catalyst.

Preparation and characterization of pure SiC ceramics by high temperature physical vapor transport induced by seeding with nano SiC particles

High temperature physical vapor transport (HTPVT) was employed to grow polycrystalline SiC ceramics with high density and purity, induced by nano SiC particles as seeds. The obtained SiC ceramics were identified as 6H-SiC with a mainly preferred orientation along the (0 0 0 6) plane, and an obvious refinement of grain size was demonstrated for the SiC seeds. Mean grain sizes of the obtained SiC ceramics were 112 μm and 314 μm, by using the SiC seeds with the mean particle size of 50 nm and 500 nm, respectively, which were obviously smaller than that of the seed-free sample (960 μm). The samples obtained with the seeds also demonstrated enhanced flexural strength and hardness, attributing to the reduced mean grain size. Furthermore, SiC ceramics without seeds via HTPVT exhibited a high thermal conductivity of 242 W·(m·K)−1 at room temperature due to the highly preferred orientation. While the degree of preferred orientation of seed-induced samples was lower, the thermal conductivity of SiC ceramics induced by seeding still maintained at least 200 W·(m·K)−1 at room temperature, this level was much higher than most other methods. Therefore, seed-induced method appears to be an effective way to control structures and behavior of SiC ceramics through HTPVT.

Synthesis of gallium-containing ZSM-5 zeolites by the seed-induced method and catalytic performance of GaZSM-5 and AlZSM-5 during the conversion of methanol to olefins

Abstract Ga isomorphically substituted HZSM-5 and AlZSM-5 with different Si/Ga and Si/Al ratios were synthesized by a seed-induced hydrothermal in situ synthesis. This strategy significantly reduced organic templates in the synthesis process. Various techniques, including XRD, SEM, TEM, XRF, NMR, N2-sorption and H2-TPR, were used in the analogy of the Ga-containing ZSM-5 zeolites and AlZSM-5. The acidities were evaluated by NH3-TPD, Py-IR and acetonitrile-TPD in detail. The Bronsted acidity of GaZSM-5 was introduced by the framework incorporation of Ga atom, which led to a lower intrinsic acid strength than incorporation of Al atom. The effect of gallium incorporation into the MFI zeolite on the catalytic lifetime and the product distribution in methanol-to-olefins (MTO) was also investigated. GaZSM-5 showed a higher amount of Lewis acid sites than did AlZSM-5. More strong acid sites, Bronsted acid sites and a higher B/L ratio have been observed for the AlZSM-5 sample, which is related to the high olefin selectivity of AlZSM-5. ZSM-5 showed higher selectivity of C2H4 and C3H6 than GaZSM-5 samples at reaction temperature of 320 °C, a space velocity of 20 h−1 and reaction time of 8 h. The selectivity of C2H4 and C3H6 over the ZSM-5 samples reached 57%.

Effects of MnO2 doping on the electrical properties of BCZT ceramics prepared by seed-induced method

The effects of MnO2 doping on the electrical properties of Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) ceramics prepared by adding 1.0 mol% BCZT seed were studied Results were found that the ceramics showed pure perovskite phase phase for all samples. Density and grain size values were in the range of 5.45–5.57 g/cm3 and 6.79–9.85 μm, respectively. The highest values of εr and Pr measured at room temperatures were 3900 and 8.22 μC/cm2, respectively which were obtained for the sample of 1.0 mol% MnO2. Tan δ of all ceramic samples was lower than 0.02. In addition, d33 and g33 values were changed with MnO2 content.

Seed-induced synthesis of flower-like a Li3V2(PO4)3/carbon composite and its application in lithium-ion batteries

Uniform, flower-like Li3V2(PO4)3/C composites were successfully synthesized using a novel, seed-induced method and were then directly applied as a cathode in lithium-ion batteries. The morphology, structure and electrochemical properties of these novel composites were examined using X-ray diffraction, scanning electron microscopy and galvanostatic charge-discharge tests. The uniform, flower-like Li3V2(PO4)3/C composites were produced on stainless steel and titanium foil substrates, but the morphology of the flowers depended on the type of substrate and the method of immersion. The Li3V2(PO4)3/C composites grown on the stainless-steel substrate exhibited the best electrochemical performance with a specific capacity of 115 mAh g−1 at the 15 C rate and a capacity retention of 94% after 500 cycles. This remarkable electrochemical performance was attributed to the formation of the perfect flower-like structure and abundance of pores in the composite. The seed-induced method proved to be a promising approach for preparing electrode materials for use in lithium ion batteries.

Direct synthesis of hierarchical ZnZSM-5 with addition of CTAB in a seeding method and improved catalytic performance in methanol to aromatics reaction

A series of ZnZSM-5 zeolites with hierarchical pores were prepared by a seed-induced method with the addition of cetyltrimethylammonium bromide (CTAB). The influence of the amounts of CTAB on the physicochemical properties of the zeolites was investigated by XRD, FTIR, SEM, TEM, N2 adsorption and desorption, ICP-OES, XPS, NH3-TPD and TG analysis. The results showed that Zn was partially incorporated in the zeolite framework; the addition of CTAB in the synthesis reduced the primary crystal size of the zeolite, but increased the specific surface area and mesopore volume. The catalytic performance of the prepared zeolites was evaluated for methanol to aromatics reaction in a fixed bed reactor. The lifetime of the catalysts was greatly enhanced by the addition of CTAB in the synthesis. The incorporation of Zn increased the selectivity of aromatics.

Zinc-Modified ZSM-5 Nanozeolites Synthesized by the Seed-Induced Method: Interrelation of Their Textural, Acidic, and Catalytic Properties in DME Conversion to Hydrocarbons

The effect of the method of introduction of zinc cations and the zinc content in a nanocrystalline zeolite of the ZSM-5 type on the physicochemical and catalytic properties of the material in DME conversion to a mixture of liquid synthetic hydrocarbons has been studied. Zinc is introduced into the catalysts both during the zeolite synthesis and the ion exchange (Zn n Al m NZ5 and ZnNZ5, respectively). The use of nanocrystalline Zn n Al m NZ5 zeolites provides the formation of a mixture of liquid hydrocarbons with a high selectivity of no less than 90%; the liquid hydrocarbons contain more than 70% of isoparaffins and a small amount of aromatic compounds. An increase in the zinc loading of the Zn n Al m NZ5 zeolite from 0.9 to ~3% leads to an increase in the methanol content in the aqueous phase of the liquid product, an increase in the selectivity for liquid hydrocarbons, and a slight increase in the concentration of aromatic and unsaturated hydrocarbons in the mixture. In the presence of the ZnNZ5/Al2O3 catalyst with Zn introduced by ion exchange, the methanol content in the aqueous phase and the aromatics content in the liquid hydrocarbon mixture are significantly higher. The Zn n Al m NZ5 nanozeolites are characterized by a more developed external surface, a higher concentration of mesopores, and higher acidity.

Synthesis of a hierarchical ZSM-11/5 composite zeolite of high SiO2/Al2O3 ratio and catalytic performance in the methanol-to-olefins reaction

A hierarchical ZSM-11/5 composite zeolite with a high SiO 2 /Al 2 O 3 ratio was successfully synthesized using a seed-induced method in the presence of cetyltrimethylammonium bromide, characterized by scanning electron microscopy, X-ray diffraction, X-ray fluorescence, 27 Al NMR, 27 Si NMR, N 2 physical adsorption, and temperature-programmed desorption of ammonia, and studied in the frame of the methanol-to-olefins reaction. The results show that the amount of seed added plays a pivotal role in the formation of hierarchical ZSM-11/5 composite zeolite. With an increase in the amount of seed, the composite zeolite exhibits excellent catalytic performance in the methanol-to-olefins reaction, which can be attributed to the higher specific surface areas, higher external surface areas, more mesopore volumes, and more acid sites than ZSM-11 synthesized by the conventional method with tetrabutylammonium ions as a template. Contrary to the conventional point of view, the addition of too much seeds results in a dramatic decrease in the catalytic performance, which is ascribed to the higher proportion of ZSM-5 in the ZSM-11/5 composite zeolite.

Aggregates of nano-sized ZSM-5 crystals synthesized with template-free and alkali-treated seeds for improving the catalytic performance in MTP reaction

A seed-induced method was developed to synthesize aggregates of nano-sized ZSM-5 crystals by template-free MFI seeds and cetyltrimethyl ammonium bromide (CTAB). Various MFI zeolites after calcination, including: nano-sized silicate-1, nano-sized ZSM-5 aggregates and commercial bulk ZSM-5 crystals were used as seeds. A trace of CTAB could accelerate the crystallization and pure MFI structure was obtained in the presence of CTAB. More importantly, the aggregates of nano-sized ZSM-5 crystals were dramatically synthesized by transforming the bulk seeds into smaller sizes with NaOH treatment before crystallization. The resulting solid exhibited an excellent catalytic performance in the methanol to propylene reaction.

Preparation of Ag2O modified silica abrasives and their chemical mechanical polishing performances on sapphire

The chemical mechanical polishing (CMP) process has become a widely accepted global planarization technology. The abrasive material is one of the key elements in CMP. In the presented paper, an Ag-doped colloidal SiO2 abrasive is synthesized by a seed-induced growth method. It is characterized by time-of-flight secondary ion mass spectroscopy and scanning electron microscopy to analyze the composition and morphology. The CMP performance of the Ag-doped colloidal silica abrasives on sapphire substrates is investigated. Experiment results show the material removal rate (MRR) of Ag-doped colloidal silica abrasives is obviously higher than that of pure colloidal silica abrasives under the same testing conditions. The surfaces that are polished by composite colloidal abrasives exhibit lower surface roughness (Ra) than those polished by pure colloidal silica abrasives. Furthermore, the acting mechanism of Ag-doped colloidal SiO2 composite abrasives in sapphire CMP is analyzed by X-ray photoelectron spectroscopy, and analytical results show that element Ag forms Ag2O which acts as a catalyst to promote the chemical effect in CMP and leads to the increasing of MRR.

Phase Transition and Electrical Properties of Ba<sub>0.8</sub>Sr<sub>0.2</sub>TiO<sub>3</sub>: Comparison of Different Preparation Techniques

This research studied the effect of the different preparation technique on phase transition and electrical properties of Ba0.8Sr0.2TiO3. The samples compared 3 preparation technique, there are conventional mix-oxide, molten-salt and seed-induced method. The samples prepared by molten-salt calcined at 800 °C, the samples prepared by conventional mix-oxide and seed-induced method was calcined at 1200 °C for 3 h. All of samples sintered at 1400 °C for 3 h. The phase formation and morphology of samples were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The dielectric properties of the samples were measurement by LCR-meter.

Aggregates of superfine ZSM-5 crystals: The effect of NaOH on the catalytic performance of methanol to propylene reaction

Loose aggregates of superfine ZSM-5 crystals (S-ZSM-5) were synthesized by a seed-induced method in the presence of cetyltrimethylammonium bromide (CTAB), characterized by XRD, SEM, N2 adsorption and desorption, XRF, NH3-TPD, 27Al MAS NMR, TG analysis, FTIR and TEM, and studied for the methanol to propylene (MTP) reaction. The results showed that CTAB played a curial role in the formation of S-ZSM-5 zeolites; NaOH concentration had a significant effect on the textural properties of S-ZSM-5 zeolites, with the morphology being controllable from cuboid to sphere by varying the NaOH/SiO2 ratios from 0 to 0.27. Compared with the catalysts synthesized by the conventional seed-induced method without CTAB, all S-ZSM-5 catalysts showed much higher stability and higher propylene selectivity in the MTP reaction. The excellent catalytic performance can be attributed to the aggregates of superfine ZSM-5 crystals with abundant mesopores and more weak acid sites, which hinder various side reactions such as hydrogen-transfer reactions.