Dry Gel Conversion Method Research Articles

Synthesis of MFI Zeolite-encapsulated Metal Nanoparticles by the Dry-gel Conversion Method and Ethane Dehydroaromatization for the Production of Valuable Chemicals

Synthesis of MFI Zeolite-encapsulated Metal Nanoparticles by the Dry-gel Conversion Method and Ethane Dehydroaromatization for the Production of Valuable Chemicals

Modified H‐BEA Zeolites from Fluorinated Silica Slag Waste by Dry Gel Conversion Method for Shape‐Selective Acylation of 2‐Methoxynaphthalene

Modified H‐BEA Zeolites from Fluorinated Silica Slag Waste by Dry Gel Conversion Method for Shape‐Selective Acylation of 2‐Methoxynaphthalene

Dry-gel conversion synthesis sponge-based MIL-160 monolith adsorbent at low temperature for water adsorption

The facile synthesis MOFs monolith adsorbent is highly imperative for the economically friendly development of water adsorption. Herein, metal-organic framework material MIL-160 monolith was synthesized by the dry-gel conversion method at low temperature. The effects of curing conditions, dry-gel composition and crystallization temperature on crystal structure, porosity, microstructure and water vapor adsorption/desorption properties were studied. XRD results showed that the MIL-160 powder and monolith adsorbent can be synthesized under the condition that the molar ratio of dry-gel was Al3+: FDCA: NaOH = 1:1:2 at 60 °C (FDCA is the abbreviation of 2,5-Furandicarboxylicacid). The water vapor saturation adsorption capacity and water vapor desorption activation energy of the powder and monolith adsorbent were 0.310, 0.231 g/g at 20 % RH and 72.3, 62.4 kJ/mol, respectively. The convenient dry-gel conversion synthesis of MIL-160 monolith may provide a guidance for the manufacture of high-performance water harvest device.

Synthesis of hierarchical Fe-incorporated ZSM-5 molecular sieves with an Fe-based metal-organic framework as a mesoporogen and iron source for catalytic pyrolysis of alkanes

To increase the yield of light olefins during the catalytic pyrolysis of alkanes, a novel hierarchical Fe-incorporated ZSM-5 molecular sieve (FeM-Z5) was synthesized using an Fe-based metal-organic framework (Fe-MOF) as a mesoporogen and iron source through the dry gel conversion (DGC) method. In contrast to the conventional method of incorporating Fe species into ZSM-5 via impregnation, the DGC method incorporates Fe species into the framework of ZSM-5, decreasing the amount of Brønsted (B) acid sites and thereby inhibiting the side reactions of hydrogen transfer during the catalytic pyrolysis of alkanes. Compared with the FeN-Z5 catalyst prepared by the DGC method with Fe(NO3)3 as an iron source, FeM-Z5 had a larger amount of strong B acid sites and more mesopores with a size range of 10–40 nm originating from the decomposition of Fe-MOF; these aspects improved n-pentane pyrolysis and ethylene and propylene diffusion. As a result, the optimal FeM-Z5 catalyst exhibited the highest yield of ethylene and propylene (33.4 wt%) and the lowest deactivation rate (0.07 %/h) among the prepared catalysts during the catalytic pyrolysis of n-pentane.

Removal of heavy metals by BEA zeolite/Fe3O4 composite prepared via dry-gel conversion method using agrowaste-derived raw material

Using agrochemicals are considered as an anthropogenic source of heavy metal contamination in water, and ecofriendly remediation tools for removal is desired. Here, we demonstrate material circulation by converting SiO2 extracted from agrowaste: rice husk ash, into an easily collectable adsorbent: BEA zeolite/Fe3O4 composite, through dry-gel conversion technique. In addition, the synthesized BEA zeolite/Fe3O4 composite was tested for removal of heavy metals for the first time. Instrumental analyses confirmed that incorporated Fe3O4 particles inside BEA zeolites showed no severe effects on its morphologies. Pseudo-second order kinetic and Langmuir isotherm models were found best described the adsorption of three typical toxic heavy metals: Pb(II), Cu(II), Zn(II). Moderate adsorption capacities of 0.675, 0.310, and 0.308 mmol/g for Pb(II), Cu(II), and Zn(II), respectively, following the selectivity order: Pb(II) > Cu(II) ≈ Zn(II) were obtained. The composite adsorbent exhibits magnetic collectability, reusability and stability, indicating its practicality for removal of heavy metals from water.

Synthesis of boron- free titanosilicate zeolite by TiCl4/HCl treatment of pure silicon MWW as an epoxidation catalyst

The pure silicon MWW were synthesized for the first time by means of a dry-gel conversion method utilizing N, N, N-trimethyl-1-adamantyl ammonium hydroxide and hexamethyleneimine as the structural directing agents. A vapor transport assisted crystallization method for obtaining complete crystallinity was developed to replace the traditional dry-gel conversion methods. TiCl4 acid solution treatment was cleverly used for the implantation of titanium in MWW. Compared with Ti-ERB-1, the Ti content of boron- free Ti-MWW is only 20% of the former, the conversion rate of 1-hexene epoxidation is 2.3 times of the former and nearly 100% of H2O2 efficiency.

Dehydrogenation–cracking synergistic pathway of n–pentane by core–shell MFI zeolite to produce light olefins

A core@shell MFI type zeolite supporting PtZn alloys catalyst was prepared by dry gel conversion method, which is used for catalytic cracking of n–pentane. The shell and core of catalyst is composed of nanosheet silicalite–1 and microporous ZSM–5, respectively. A proposed dehydrogenation–cracking pathway was demonstrated, which facilitate the generation of light olefins. At 600 °C with WHSV of 6.26 h−1, the yield of ethylene and propylene in the product attained up to 35.3 wt% and 33.4 wt%, respectively.

Catalytic pyrolysis of rice husk over defect-rich beta zeolites for biofuel production

The Coats-Redfern method was used to identify the catalytic and non-catalytic pyrolysis of rice husk biomass kinetics by using thermogravimetric analysis. MTES-beta-zeolite and beta-zeolite were synthesized by dry gel conversion method. Both synthesized zeolites and commercial beta-zeolite were mixed with ground rice husk in a 1:0.03 ratio by mass. Thermal degradation for catalytic and non-catalytic pyrolysis of rice husk biomass occurred at 523 K to 823 K. Conversions were majorly observed in Section I (523–633 K) and Section II (723–823 K) temperature ranges. Order and diffusion-based models were in approximation with each other for both temperature ranges. From the Ea trends, it can be understood that MTES beta-zeolite has no significant effect on pyrolysis in Section I and has promising results in Section II. The beta-zeolite and commercial beta-zeolite gave better results for all reaction models in both sections by lowering the activation energies for catalytic pyrolysis of RH compared to those for non-catalytic pyrolysis. By comparing catalytic with non-catalytic pyrolysis of rice husk, activation energy significantly varied for both sections. Thermodynamic parameters (ΔH) and (ΔG) values indicated the activated complex formation and non-spontaneity of the reaction. The negative value of (ΔS) suggested a more ordered state. Furthermore, pyrolysis of rice husk with commercial beta zeolite was performed and biochar produced with a yield of approximately 75%. Different organic compounds were also obtained in the bio-oil which include different aliphatic compounds.

Utilization of agricultural waste to herbicide removal: Magnetic BEA zeolite adsorbents prepared by dry-gel conversion using rice husk ash–derived SiO2 for paraquat removal

This study presents a method that will allow for the sustainable utilization of rice husk ash-SiO2 (RHAS), an agricultural-waste–derived material, as a bulky solid SiO2 source in the zeolite beta (BEA)/Fe3O4 composite (magnetic RHAS-BEA) synthesis via a dry-gel conversion method for the removal of paraquat, a typical herbicide, from aqueous solutions. Ultrasonic waves were used to facilitate the formation of uniform Fe3O4-contained dry precursor gel before converting to the magnetic BEA zeolite composite for the first time. Magnetic RHAS-BEA was then characterized and compared with a non-magnetic sample (RHAS-BEA) using X-ray diffraction and field-emission scanning electron microscopy. In terms of adsorption, we found that paraquat had a high adsorption rate on the samples and conformed to a pseudo-second-order kinetic model. The adsorption behavior of paraquat on the synthesized RHAS-BEA and magnetic RHAS-BEA obeyed the Langmuir adsorption isotherm model. The synthesized adsorbents were reusable for at least four cycles, via thermal regeneration at 450 °C. The inclusion of Fe3O4 particles in magnetic RHAS-BEA disrupted neither the crystallization of the BEA zeolite nor the adsorption of paraquat and enabled easy collection via an external magnet.

A Novel Strategy to Enhance Acid Strength of Zeolites by Incorporating Ge into Zeolite Framework

AbstractIn the long history of zeolite research, further enhancement of their acid strength has looked difficult. In this study, we achieved the enhancement by incorporating Ge into the zeolite framework. We synthesised the zeolites by a dry gel conversion method and characterised them in terms of morphology, crystal structure, and composition. We determined the acid strength of these zeolites by calculating the change in the enthalpy of desorption in the temperature‐programmed desorption of ammonia and confirmed that the acid strength of the zeolites with Ge was higher than that of a conventional zeolite. This enhancement of acid strength probably originated from the unprecedented interactions between Al and Ge, unlike the conventional interactions between Al and Si. The enhanced acid strength led to high efficiency of ethanol‐to‐propylene reactions, affording higher yield of propylene than that obtained using conventional zeolites.

In situ synthesis of Pt nanoparticles encapsulated in silicalite-1 zeolite via a steam-assisted dry-gel conversion method

Pt NPs with high thermal stability and activity were directly encapsulated in MFI-type zeolite via a steam-assisted dry-gel conversion method.

Defect engineering to boost catalytic activity of Beta zeolite on low-density polyethylene cracking

Catalytic cracking is of considerable interest as a sustainable, renewable, efficient, and eco-friendly chemical conversion method of plastic wastes. In catalytic cracking, plastic wastes can be converted into valuable products such as monomers or petrochemical feedstock. Solid acid catalysts, especially zeolites, significantly lower the thermal decomposition temperature of plastics. However, the catalysts have not shown enough performance to be implemented in society. Therefore, major efforts have recently been devoted to solving this problem by appropriately designing zeolite catalysts. Herein, we report a new defect-rich Beta zeolite synthesized by a dry gel conversion method using methyltriethoxysilane. The obtained catalyst exhibited outstanding activity on low-density polyethylene cracking. We measured Fourier-transform infrared spectra using pyridine as a probe molecule and found that this high activity is contributed by the increase of the amount of Lewis acid sites. It probably arises from the ratios of extra-framework hexacoordinated aluminum and silanol groups higher than the conventional Beta zeolite shown in 27Al and 1H magic angle spinning nuclear magnetic resonance spectra. We can say that the increase of defects of zeolite Beta further accelerated polymer cracking. This work provides a new strategy to improve the catalytic activity of zeolites on polymer cracking.

Self-Etherification of 5-Hydroxymethylfurfural to 5,5′(Oxy-bis(methylene))bis-2-furfural over Hierarchically Micromesoporous ZSM-5: The Role of Brønsted- and Lewis-Acid Sites

The 5,5′(oxy-bis(methylene))bis-2-furfural (OBMF) formation from the 5-hydroxymethylfurfural (HMF) self-etherification over zeolites is an important reaction for the synthesis of value-added chemicals from biomass resources. However, there is still a lack of knowledge about the reaction mechanism and the roles of different acid sites that impedes the exploitation of zeolite catalysts for efficient OBMF production. In the present study, the ZSM-5 (HPZ) catalysts of four hierarchically micromesopores were successfully synthesized in different Si/Al ratios by adjusting the amount of Al in the solvent evaporation with the assistance of a dry gel conversion method. The kinetics of OBMF formation from HMF self-etherification was investigated. The apparent activation energy and the conversion reaction order were calculated to be 104.6 kJ/mol and 0.65, respectively. The intrinsic activity comparison of four catalysts and density functional theory (DFT) calculations showed that HMF adsorption and etherification benefit from Brønsted-acid sites. Besides, the DFT results suggested that the etherification proceeds via a concerted step, instead of the sequential pathways, thus leading to the high selectivity of OBMF on hierarchically micromesoporous ZSM-5 (HPZ) catalysts.

Synthesis of SAPO-34 using the different combinations of four templates by dry gel conversion method

Synthesis of SAPO-34 using the different combinations of four templates by dry gel conversion method

Direct synthesis of Zn-incorporated nano-ZSM-5 zeolite by a dry gel conversion method for improving catalytic performance of methanol to aromatics reaction

Direct synthesis of Zn-incorporated nano-ZSM-5 zeolite by a dry gel conversion method for improving catalytic performance of methanol to aromatics reaction

Synthesis of nano-ZSM-5 zeolite via a dry gel conversion crystallization process and its application in MTO reaction

Nano-sized ZSM-5 with superior catalytic properties was synthesized from LAPONITE® as one of the Si sources by a dry gel conversion method.

On the Anti-Corrosion Property of Dry-Gel-Conversion-Grown MFI Zeolite Coating on Aluminum Alloy.

MFI zeolite film coated on AA6061 alloy was prepared from fumed silica modified with/without n-octyldecyltrimethoxysilane (ODS) by means of dry gel conversion (DGC) method. The DGC-grown MFI zeolite film could form a strong barrier to protect AA6061 surface against the corrosion from NaCl solution. By using fumed silica as a starting material, the hydrophilicity and anti-corrosion capability of the MFI zeolite film declined with increasing humidity in the DGC synthesis. By silanization with ODS, the surface hydrophobicity of the MFI zeolite film increased, leading to substantial enhancement in anti-corrosion capability. On the other hand, MFI film grown from ODS-modified fumed silica exhibited low hydrophilicity and a much improved anti-corrosion protection property by four orders of magnitude, even stronger than the ODS post-treated MFI film. The strong anti-corrosion capability is attributed to the “thick layer” surface hydrophobicity of zeolite crystal.

One-step synthesis of bi-functional zeolite catalyst with highly exposed octahedral Co for efficient epoxidation of bulky cycloalkenes

Bi-functional zeolite catalyst, incorporated with both organic groups and transition metal ions, has been firstly one-step synthesized by dry gel conversion method, which is characterized by powder XRD, solid-state 27Al, 29Si, 13C MAS NMR, FT-IR, Raman, UV–vis, X-ray photoelectron spectroscopy, and so on. Notably, the SiO/SiI ratio in the synthesis gel has important influence on the coordination state and distribution of cobalt species in the hybrid zeolite. Low SiO/SiI ratio has accelerated the formation of hybrid zeolite with tetrahedral framework cobalt while high SiO/SiI ratio has accelerated the additional assembly of hybrid zeolite with octahedral extra-framework cobalt. In the catalytic epoxidation of bulky cycloalkenes with air, hybrid zeolite with both tetrahedral framework cobalt and octahedral extra-framework cobalt shows the most excellent catalytic performance and TON value, compared with pure inorganic zeolite, hybrid zeolites with only tetrahedral framework cobalt species, and hybrid zeolites with Co species introduced by ion-exchange or wet impregnation methods, which is ascribed to the synergistic roles of organic groups and cobalt species. On one hand, the highly exposed octahedral extra-framework cobalt species act as an efficient supplement of tetrahedral framework cobalt, and the interactions of accessible catalytic active sites with bulky cycloalkene molecules have been strengthened greatly. On the other hand, mercaptopropyl groups are beneficial for the formation of stable heterogeneous catalyst with lipophilic surface through anchoring the extra-framework cobalt species and modifying the surface of the zeolite, which accelerate the epoxidation reaction efficiently.

Controllable synthesis of Si-DD3R molecular sieves nanocrystalline by microwave assisting dry-gel conversion method

All-silica Deca-Dodecasil 3 Rhombohedral (Si-DD3R) type zeolite with a two-dimensional pore system is a very attractive size selective adsorbent which enables only small molecules to adsorb. It is a great potential candidate in the fields of separation and catalysis. In this work, nanocrystalline Si-DD3R molecular sieves with the particle size of about 30 nm were synthesized by microwave assisting dry-gel conversion (MADGC) method. The advantages of microwave radiation, HF and dry-gel conversion (DGC) were well combined and effectively decrease the size and in situ synthesis time. At 433 K, highly uniform nancrystalline Si-DD3R was obtained in 7 h without seeding. When the partial pressure was 1.0 bar, the CO2 adsorbed amount reached about 0.83 mmol g−1. The zeolites are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM).

Positive Role of Synthesis Method and Hard Template on the Catalytic Performance of SAPO-34 in Methanol to Olefin Reaction

In the present study, SAPO-34 particles were synthesized using hydrothermal (HT) and dry gel (DG) conversion methods in the presence of diethyl amine (DEA) as an organic structure directing agent (SDA). Carbon nanotubes (CNT) were used as a hard template in the synthesis procedure to introduce transport pores into the structures of the synthesized samples. The synthesized samples were characterized with different methods to reveal the effects of synthesis method and using hard template on their structure and catalytic performance in methanol to olefin reaction (MTO). DG conversion method results in smaller particle size in comparison with hydrothermal method, resulting in enhancing catalytic performance. On the other side, using CNT in the synthesis procedure with DG method results in more reduction in particle size and formation of hierarchical structure, which drastically improves catalytic performance.