Synthesis Of Molecular Sieves Research Articles

Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV–Vis (DRS), FT-IR, N2 adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH3-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV–Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.

Effect of kaolin calcined temperature on the preparation and crystallization mechanism of SAPO-34 molecular sieve for methanol-to-olefins performance

SAPO-34 molecular sieves synthesized using calcined kaolin as partial raw material under three-stage of high-low-high temperature hydrothermal condition are explored systematically. Especially, the effect of kaolin calcination temperature on the crystallization mechanism of SAPO-34 and the methanol to olefin performance are investigated thoroughly. It is found that the sample (SP-500) synthesized by using kaolin calcined at 500 °C (MK-500) demonstrates clean cubic structure, large specific surface area and mild acidity, providing the initially activated Si and Al source for the synthesis of SAPO-34 molecular sieve due to the well scattered structure of MK-500. From the crystallization mechanism consideration, it can be proposed that the SAPO-34 molecular sieves will be controlled by the low degree of Si aggregation in metakaolin and quantity of Si (3Al,1Si) species. As a result, SP-500 displays excellent catalytic lifetime during methanol to olefin reaction for its special Si coordination environment, showing the highest stable light olefin yield of 80.6 % and a methanol conversion above 90 % for more than 720 min. In contrast, SP-800 sample with the most strong acid sites is only 390 min, even if showcasing the highest selectivity of light olefins (84.5%).

Ultrafast and continuous synthesis of an aluminophosphate type zeolite in microchannel and the hydrogenation of α-pinene

A highly efficient method was proposed for fast and continuous synthesis of LTA-type aluminophosphate (AlPO4-LTA) molecular sieves. The precursor was first synthesized in batch methods, then the precursor and tetramethyllamine hydroxide were coordinated to direct the synthesis of molecular sieves in a reaction system containing a poly (tetrafluoroethylene) (PTFE) microchannel reactor, which reduced the energy costs associated with mixing and cooling of reactant solutions. The reaction conditions, including molar ratio of reagents, temperature and flow rate, have also been rapidly optimized. The AlPO4-LTA have high crystallinity, high thermal stability, granule size (ca. 150 nm) and large surface area (679 m2/g). In addition, the hydrogenation of α-pinene catalyzed by Ni/AlPO4 nanocomposites was achieved with α-pinene conversion rate of 95.1% and cis-pinane selectivity of 95.9%, the catalyst had high activity during five cycles.

Exploring the effect of polyacrylamide/graphene oxide composite hydrogel on the synthesis and application of ZSM-5 molecular sieves

Herein, we demonstrate the synthesis of coffin-shaped ZSM-5 molecular sieves in polyacrylamide (PAM)/graphene oxide (GO) composite hydrogel using the hydrothermal method. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), and Thermogravimetry analyses (TGA). The effect of PAM and GO addition on the morphology and structure of ZSM-5 was investigated. The results indicated that the introduction of PAM and GO promoted the growth of the ZSM-5 (101) plane. Moreover, samples synthesized in the PAM/GO hydrogel exhibited a longer c-axis and a more pronounced coffin-shaped morphology compared to samples synthesized solely in PAM hydrogel. The Si/Al ratio decreased with the addition of GO, possibly due to interface effects leading to the formation of ZSM-5 precursors with a higher Al content. TG, FT-IR, and XPS characterization revealed hydrogen bonding interactions between PAM and GO, and the addition of GO likely restricted the movement of polymers, improving cross-linking between monomers and forming a more uniform network structure. The sample G-15 (P-5) exhibited higher mesopore volume and average pore diameter, contributing to enhanced catalytic performance. However, with increasing GO content, the average pore diameter decreased, potentially due to functional groups on the surfaces of graphene oxide and polyacrylamide forming a more uniform and structurally stable three-dimensional network structure. This allowed for controlled modulation of the molecular sieve morphology and pore size. The introduction of PAM/GO hydrogel resulted in a moderate amount of weak acid and an increased amount of strong acid, both shifting to lower temperatures. The ZSM-5 molecular sieves synthesized in the PAM/GO composite hydrogel demonstrated outstanding MTO catalytic performance, exhibiting high selectivity for light olefins and an extended catalytic lifespan. This work is expected to provide new ideas and methods for developing efficient ZSM-5 catalysts.

Synthesis of a high-iron fly-ash-based Na-X molecular sieve and its application in the adsorption of low concentration of CO2.

In addressing the environmental challenges posed by the accumulation of fly ash (FA), efforts have been geared towards its high-value utilization. By the use of high-iron FA as a raw material, a high-iron fly-ash-based Na-X molecular sieve was successfully synthesized by hydrothermal method. We combined pretreatment methods such as high-temperature calcination, acid leaching and alkali fusion activation. The as-synthesized product was used for the adsorption of a low concentration of CO2, and the adsorption data were fitted by a physical model. The changes in iron content in pretreatment and molecular sieve synthesis were revealed by SEM-mapping, UV-Raman and UV-Vis. The results showed that the pretreatment process reduces the iron content from 32.3% to 13.3%, and converts the inactive phases to active phases, with n (SiO2/Al2O3) = 4.94. The activated product was transformed further to a Na-X molecular sieve using a hydrothermal method. The product has a single crystal phase and octahedral crystal structure. Its specific surface area was 646.634 m2 g-1, and micropores were distributed between 0.46 nm and 0.71 nm, with a mesoporous phase of 4.6 nm. When used to adsorb a low concentration of CO2, the Na-X molecular sieve has a high adsorption capacity of 3.70 mmol g-1, which reaches 95.11% that of the commercial Na-X molecular sieve. The adsorption breakthrough time and adsorption capacity decreased with an increase in temperature. The adsorption kinetics were consistent with the Bangham model for surface pore adsorption and Weber-Morris model for internal diffusion. During the synthesis process, iron was converted from highly dispersed iron oxide to four-coordinated framework iron. Thus, this paper paves a path for the high-quality transformation and utilization of high-iron fly-ash.

Ultra-fast synthesis of hierarchical SAPO-11 molecular sieves with the assistance of hydroxyl radicals.

Considering the traditional time-consuming synthesis route and diffusion-limited micropore system of SAPO-11 (i.e., SAPO-11W), a hydroxyl radical assisted method has been developed to prepare hierarchical SAPO-11 within 5 min (i.e., SAPO-11M). Compared to previous reports, the unique contribution is to induce hydroxyl radicals by exposing carbon materials to microwave irradiation in an oxygen-containing atmosphere. Carbon materials play a dual role as mesopore filler and hydroxyl radical initiator. When employed to prepare deoxygenation catalysts for stearic acids, a higher selectivity for C15-C18 and isomers is observed due to the mild acidity of SAPO-11M. The Lewis-rich acidity of SAPO-11M exhibits an electron deficiency to interact with the hydroxyl oxygen atoms and promotes the hydrodeoxygenation of stearic acids with excellent atom economy. These results are important for opening up a new prospect of synthesizing SAPO molecular sieves (e.g., SAPO-11 and SAPO-5) by an efficient and facile route.

Tailored synthesis of plate-like SAPO-11 molecular sieve and its application in non-noble metal-supported catalyst for efficient hydroisomerization of long-chain n-alkanes

The tailored synthesis of plate-like SAPO-11 molecular sieve was achieved by introducing seed-surfactant directing agent into the synthesis system for the first time. The effects of morphological change of SAPO-11 molecular sieve on the physicochemical properties of SAPO-11 and the active phase properties of the catalyst were analyzed via a series of characterization techniques. The hydroisomerization of n-hexadecane was used as the model reaction to evaluate the catalytic performance of NiWS supported catalysts based on SAPO-11 molecular sieve with different morphologies. The plate-like SAPO-11 possessed better textural properties and acidity than pseudo-spherical SAPO-11. Meanwhile, the stacking number, dispersion and metal sulfidation degree of the active phase of sulfided NiW/SAPO-11-P were improved, and its high proportion of type II active phase optimized the metal–acid synergistic catalytic mechanism. Through tracking and analyzing the crystallization process of plate-like SAPO-11, the formation mechanism of plate-like SAPO-11 was investigated and revealed. The adsorption kinetics, diffusion behavior and catalytic kinetics of n-hexadecane on the catalysts were emphatically investigated. The optimized support structure and active phase properties improved the intrinsic catalytic activity and hydroisomerization reaction path priority of NiW/SAPO-11-P. It was found that the hydroisomerization reaction on NiW/SAPO-11-P was carried out under the reaction-limiting conditions, while the hydroisomerization reaction on NiW/SAPO-11-C was carried out under the reaction-controlling conditions. The effects of plate-like SAPO-11 on the activity stability of the catalyst was investigated, and the essential reasons for the differences in activity stability of the catalysts were revealed through comprehensively analyzing the coke formation difference and diffusion behavior difference. It is expected to provide reference for the tailored design of SAPO-11 molecular sieve with special morphology and the preparation of efficient hydroisomerization catalyst.

Synthesis of a loess-based 4A molecular sieve and its application performance in detergents

Herein, activated loess was obtained via acidification and alkalisation and was mixed with sodium hydroxide, water and aluminium sulphate to prepare a loess-based 4A molecular sieve using the hydrothermal conversion method. The sieve performance was characterised, and the effect of raw materials and reaction conditions on the sieve was investigated. Results showed that it exhibits different microstructures according to its crystallinity and impurity content. Moreover, the amount of sodium hydroxide and the reaction temperature had a substantial influence on its synthesis, while water and the reaction time exhibited less influence. The synthesis method was optimal when the reaction temperature was 90 °C, reaction time was 4 h, pH was ∼ 13 and the mixture ratio was SiO2:Al2O3:H2O:NaOH = 1.9:1:213:12. Finally, the application performance of the molecular sieve in detergents was studied. The sieve showed complete adherence to the National Standard of Detergent in China (GB/T 1767–2003).

Rapid synthesis of SAPO-34 molecular sieve with cheap template for improving MTO performance

Low-silicon SAPO-34 was rapidly synthesized with the assistance of citric acid using inexpensive triethylamine as a template. The effects of citric acid on the crystal structure, morphology, and acidity were investigated using XRD, SEM, FT-IR as well as ICP characterization methods. The results show that citric acid promotes the growth of SAPO-34, shortens the crystallization time and improves the yield of solids. Furthermore, citric acid facilitates the synthesis of low-silicon SAPO-34, which exhibits improved MTO catalytic performance. Compared with conventional SAPO-34, low-silicon SAPO-34 generated higher selectivity of ethylene and propylene.

Synthesis of 2D type A molecular sieves by alkaline removal of natural kaolin

Type A molecular sieves have been extensively employed in various fields. It is noteworthy that the direct synthesis of type A molecular sieves from natural kaolin is a common practice among researchers. Traditional type A molecular sieves are characterized by a three-dimensional cubic lattice structure. In this study, our objective is to facilitate the transformation of type A molecular sieves into a two-dimensional layered configuration by employing a two-dimensional layered material as a templating agent. In this research, natural kaolin serves as the primary source material. To eliminate impurities including quartz, illite, and dolomite, an alkali-based solvent extraction method is employed, yielding amorphous silicon and aluminum compounds. Subsequently, a graphene-based templating agent is introduced, and a hydrothermal synthesis process is employed to fabricate two-dimensional type A molecular sieves. The method described herein yields two-dimensional layered type A molecular sieves with a crystallinity exceeding 90%, thereby resulting in a specific surface area that is approximately 11-fold greater compared to their three-dimensional type A counterparts. The applicability of this methodology can be extended to the valorization of low-grade natural mineral resources, optimizing their utility. Furthermore, the approach presented herein for the synthesis of two-dimensional molecular sieves is of a universal nature, offering valuable insights that can serve as a reference for the synthesis of various other categories of two-dimensional molecular sieves.

Novel synthesis strategy of SAPO-11 molecular sieve with superior performance for hydroisomerization of long-chain n-alkanes: Supergravity-cyclone assisted hydrothermal crystallization method

In this work, we successfully synthesized high performance SAPO-11 molecular sieve via the novel supergravity-cyclone assisted hydrothermal crystallization method for the first time. The initial gel was subjected to cyclone treatment and supergravity shearing treatment to obtain the secondary molecular sieve precursor mixture with high viscosity and micro-bubble distribution. The effects of supergravity shear-cyclone operation on the physicochemical properties of SAPO-11 molecular sieve were investigated. The supergravity-cyclone treatment improved the textural properties and acidity of SAPO-11 molecular sieve. The effects of support properties on the properties of active phase of NiWS-support catalyst and its catalytic performance for hydroisomerization of n-hexadecane were further investigated. NiW/SAPO-11-B showed more active phase with hydroisomerization kinetics advantage and nearly doubled yield of i-hexadecane compared with conventional SAPO-11-based catalyst. The process and mechanism of synthesizing high performance SAPO-11 molecular sieve via the supergravity-cyclone technology were explored. It was found that the supergravity-cyclone assisted crystallization method shortened the crystallization time of SAPO-11 and improved the crystallization efficiency. In addition, the hydroisomerization kinetics of n-hexadecane on SAPO-11-based NiWS supported catalyst was studied. The structure–activity relationship between the structure of active phase and the formation of CUS was investigated, and the influence of support properties on the properties of NiWS active phase and their synergistic mechanism in the hydroisomerization of n-hexadecane were revealed. This is expected to provide a new strategy for the synthesis of high performance SAPO-11 molecular sieve and the preparation of non-noble metal supported catalyst with superior hydroisomerization performance for long-chain alkanes.

Synthesis and mechanism of porous molecular sieves

Porous molecular sieve was a kind of material with different pore structure. Porous molecular sieve had molecular sieve separation ability and rapid mass transfer ability. These materials effectively solved the mass transmission problem of traditional molecular sieve. And allowed substrate molecules to enter the active site located in the micropore, thus improving the reaction rate and lifetime. In addition, the secondary porosity of the porous zeolite created an ideal space for the deposition of the products, controlling their size and allowing high dispersion and strong interactions between the zeolite and the medium. In this paper, the synthesis and mechanism of porous molecular sieve were summarized and summarized, which laid a theoretical foundation for the synthesis of porous molecular sieve.

Synthesis of spherical amine-functionalized silica molecular sieve and application as selective adsorbents for aromatic hydrocarbons analysis

In this work, spherical amine-functionalized mesoporous silica (Sp-Amino-Si) molecular sieve was fabricated by an acid hydrothermal method using 3-aminopropyltriethoxysilane as a modifier and toluene as the solvent. The results of scanning electron microscopy, Barrett-Joyner-Halenda pore size distribution, Fourier transform-infrared spectroscopy, and low-angle X-ray diffraction patterns revealed that the Sp-Amino-Si was monodispersed microspheres with uniform and controllable pore sizes sharing two-dimensional hexagonal P6mm symmetry and a large number of amino groups. The Sp-Amino-Si molecular sieve was verified to be suitable for the selective separation of aromatic hydrocarbons (AMHs) containing two fused benzene rings among other compounds from environmental water matrix. Under the optimized conditions, the Sp-Amino-Si exhibited much higher adsorption efficiency for AMHs (above 88.19%), comparing to the original SBA-15 (below 44.52%). The maximum adsorption capacities for naphthalene, methyl naphthalene, 2-methyl naphthalene, and acenaphthene were 477.1, 1006.5, 893.3, and 1253.2 µg·g−1, respectively. The high selectivity of Sp-Amino-Si for the four AMHs attributed to the size sieving and p-π interactions between the lone pair electrons of amine groups and the π-electrons in AMHs molecules. The Sp-Amino-Si based solid-phase extraction coupled with high performance liquid chromatography detection method was constructed for the analysis of the four AMHs, and the recoveries of spiked AMHs ranged from 89.67% to 112.74% with a relative standard deviation lower than 5.75%. This study provides some inspiration and a reliable method for AMHs separation, removal, and analysis.

Study on Synthesis of Molecular Sieve from Potash Feldspar Calcined by KOH at Medium Temperature

Study on Synthesis of Molecular Sieve from Potash Feldspar Calcined by KOH at Medium Temperature

Functional mesoporous materials in clean energy: an interview with Dongyuan Zhao

ABSTRACT National Science Review invited Prof. Dongyuan Zhao of Fudan University for an interview focusing on his team's renowned research on functional mesoporous materials and energy-related applications. Prof. Zhao is a professor of chemistry and materials science, and a member of the Chinese Academy of Sciences. He received his PhD in chemistry from Jilin University in 1990. He has since focused his research on the synthesis and structure of porous materials and molecular sieves. His team received a first-tier national science award in 2021 for their contribution to the research and development of mesoscopic materials. They discovered a method of synthesizing mesoporous organic polymers and carbonaceous materials using organic-organic self-assembly. This work was published in 2005 and since then it has turned into a vibrant new field of more than 40 000 publications so far. His team has named more than 20 of their inventions after Fudan University: the FDU mesoporous series.

Preparation and humidity control performance of aluminum containing mesoporous molecular sieve synthesis from liquid crystal display waste glass and sandblasting waste

Preparation and humidity control performance of aluminum containing mesoporous molecular sieve synthesis from liquid crystal display waste glass and sandblasting waste

The effects of templates and seeds on the properties of nanosheet SAPO-34 molecular sieves and their catalytic performance in the MTO reaction

Nanoscale SAPO-34 molecular sieves were synthesized by adding different types of seed into hydrothermal synthesis systems with tetraethylammonium hydroxide (TEAOH) and triethylamine (TEA) & tetraethylammonium bromide (TEABr) as templates. The effects of different types of template and seed on the crystal structure, morphology, grain size and acidity of the molecular sieves were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 isothermal adsorption–desorption and ammonia temperature-programmed desorption (NH3-TPD). The methanol-to-olefins (MTO) reaction performance of the synthesized samples was investigated in a fixed-bed reactor. The results showed that crystalline supernatant and seed soaking solution could be used as liquid seeds to assist in the synthesis of SAPO-34 molecular sieves with a lamellar structure. The yield of SAPO-34 synthesized by seed increased from 38.64 to 59.68%, and the methanol conversion rate was significantly improved as compared with that of SAPO-34 synthesized without seed. The nano-thickness of SAPO-34 synthesized with TEA&TEABr instead of TEAOH as template decreased from 100–150 to 40–50 nm, and the lifetime increased from 360 to 400 min with the original yield kept constant.

Rapid synthesis of hierarchical silicoaluminophosphate molecular sieves using carbon-silicon composites from rice husk ash for deoxygenation of stearic acids

To improve the low temperature fluidity of bio-diesel, a Ni/SAPO catalyst is prepared using hierarchical silicoaluminophosphate (i.e., SAPO-11/SAPO-31) molecular sieves as supports. A rapid, cost-effective, and eco-friendly approach is proposed using carbon-silicon composites from rice husk ash (RHA). The carbon-silicon composite is obtained via an anaerobic calcination of RHA, which acts as the silicon source and mesopore filler, simultaneously. As-synthesized SAPO-11/SAPO-31 intergrowth molecular sieve has a high mesopore volume due to the mesopore filler function of carbon in RHA. A lower crystallization temperature and shorter duration are achieved with the assistance of microwave irradiation. Ni/SAPO catalysts exhibit a high conversion of stearic acids (concentration, 0.5–5 wt%) to form n-/isoparaffins. These results are important to develop a potential efficient catalyst for the upgrade of bio-oil and the novel synthesis method provides reference to the synthesis of other types of SAPO molecular sieves.

Template-free synthesis of silicon‑aluminum intergrowth molecular sieves using industrial residues without pretreatments for producing 5-hydroxymethylfurfural (5-HMF)

As a silicon‑aluminum solid waste in the preparation of fluid catalytic cracking (FCC) catalysts, residues (named as FCCR) are directly employed as synthesis raw materials without any pretreatments. An eco-friendly and template-free route is proposed to prepare ZSM-5/mordenite intergrowth molecular sieves using FCCR via a microwave assisted hydrothermal method. ZSM-5/mordenite intergrowth molecular sieves with controllable porosity and acidity are obtained. The proportion of ZSM-5 or mordenite molecular sieves is regulated by optimizing synthesis conditions (e.g., amount of seed, heating temperature/ duration, alkalinity, and SiO2/Al2O3). ZSM-5/mordenite intergrowth molecular sieves exhibit catalytic performance in the dehydration reaction of glucose to prepare 5-hydroxymethylfurfural (5-HMF). The in-situ FTIR approach proves a dehydration route “glucose→fructose→5-HMF” under the synergistic effect of BrØnsted and Lewis acid sites. These results are important for the disposal of FCCR and eco-friendly synthesis of molecular sieves.

Facile synthesis of NaY molecular sieve by low-temperature ultrasonic gelling method for efficient adsorption of rare-earth elements

Due to the lack of rare earth resources, the recovery of rare earth ions from industrial wastewater has been widely concerned. In this work, NaY molecular sieve was synthesized at 50–90 °C for 3–10 h without template and guide agent by low-temperature ultrasonic gelling method, and it was examined as the adsorbent to recover and enrich La3+ and Eu3+ in synthetic rare earth liquids. The properties of the synthesized NaY crystallization at 90 °C for 5 h were determined as follows: relative crystallinity of 99.49%, average particle size of 300 nm, specific surface area of 873.66 m2/g, and average aperture of 0.5617 nm. When the adsorption temperature was 25 °C, the pH was about 7, the initial concentrations of La3+ and Eu3+ were 227.00 mg/L and 195.30 mg/L, respectively, the amount of NaY was 0.01 g, and the volume of the rare earth simulant was 10 ml, the unit adsorption capacity and adsorption efficiency of La3+ were respectively 174.12 mg/g and 75.30%, and the unit adsorption capacity and adsorption efficiency of Eu3+ were 147.47 mg/g and 75.51%, respectively. After four cycles, the unit adsorption efficiency of La3+ and Eu3+ were still respectively 93.20 mg/g and 91.00 mg/g. The adsorption process showed a closer agreement with Langmuir isotherm and quasi-second-order kinetics model. The results indicate that this NaY molecular sieve is a promising adsorbent for rare earth recycling and enrichment from wastewater.