Zeolite Precursor Research Articles

Synthesis of MFI zeolites with hierarchical porosity by dry‐gel conversion

AbstractDry‐gel conversion (DGC), which directly converts zeolite gel into crystals by vapor, is considered a promising method for reducing amounts of zeolite precursors and easily controlling crystallization. Synthesis of MFI zeolites employing the DGC method with different amounts of tetrapropylammonium bromide (TPABr) and sodium hydroxide (NaOH) was studied to investigate the effect of TPABr and NaOH on the crystallization of MFI zeolite, with the optimal condition for synthesis found to be 0.05625 for both NaOH/SiO2 and TPABr/SiO2. Additionally, carbon black (CB) was added onto the MFI zeolite precursor gel as a hard template to generate mesopores into zeolite frameworks. The resultant MFI zeolite with CB synthesized by the DGC method showed mesoporosity, with pore size distribution similar to the particle size of CB. However, the conventional hydrothermal method could not generate mesopores in MFI zeolite due to the separation of zeolite crystals from CB templates during crystallization.

Amino Acid-Assisted Synthesis of Zeolites with Improved Catalytic Properties.

Conventional zeolites are limited in their ability to catalyze macromolecular reactions due to micropore constraints, resulting in sluggish reactant and product diffusion and subsequently pore clogging and catalyst deactivation. Consequently, the pore and textural refinement of zeolites to meet industrial demands has become a research hotspot. Herein, we review the amino acid-assisted methods in zeolite synthesis and scrutinize the principle and influential factors governing amino acid involvement in zeolite synthesis. Additionally, we analyze the advantages and challenges associated with the amino acid-assisted method. Certain amino acids can interact with zeolite precursors or crystal surface, thus altering the crystal growth rate and enabling precise control over the crystal size and shape. On the other hand, amino acids can serve as structure-directing agents to orchestrate the generation of mesoporous pores. These capabilities enable the production of zeolites with well-defined pores, particle sizes and/or crystal shapes that satisfy catalytic requirements. Moreover, the unique properties of amino acids allow their complete elimination from the solid product through a simple aqueous washing process, facilitating their recovery for subsequent usage. As result, the amino acid-assisted synthesis methods offer a convenient, green route to zeolites with modulated textual properties for high-performance catalysis.

Magnetic CuFe2O4 Nanoparticles Immobilized on Modified Rice Husk-Derived Zeolite for Chlorogenic Acid Adsorption

Adsorption has emerged as a promising method for removing polyphenols in water remediation. This work explores chlorogenic acid (CGA) adsorption on zeolite-based magnetic nanocomposites synthesized from rice husk waste. In particular, enhanced adsorbing materials were attained using a hydrothermal zeolite precursor (Z18) synthesized from rice husk and possessing a remarkable specific surface area (217.69 m2 g−1). A composite material was prepared by immobilizing magnetic copper ferrite on Z18 (Z18:CuFe2O4) to recover the zeolite adsorbent. In addition, Z18 was modified (Z18 M) with a mixture of 3-aminopropyltriethoxysilane (APTES) and trimethylchlorosilane (TMCS) to improve the affinity towards organic compounds in the final nanocomposite system (Z18 M:CuFe2O4). While the unmodified composite demonstrated inconsequential CGA removal rates, Z18 M:CuFe2O4 could adsorb 89.35% of CGA within the first hour of operation. Z18 M:CuFe2O4 showed no toxicity for seed germination and achieved a mass recovery of 85% (due to a saturation magnetization of 4.1 emu g−1) when an external magnetic field was applied. These results suggest that adsorbing magnetic nanocomposites are amenable to CGA polyphenol removal from wastewater. Furthermore, the reuse, revalorization, and conversion into value-added materials of agro-industrial waste may allow the opportunity to implement sustainability and work towards a circular economy.

Ni phosphide catalysts on Al2O3‐zeolite prepared by phosphidation for methyl palmitate hydroconversion

AbstractBACKGROUNDOne‐stage hydroconversion of fatty‐acid based feedstocks is a promising way to obtain high‐quality fuels. This process is based on hydrodeoxygenation, isomerization and hydrocracking reactions. In this work, Ni2P/Al2O3‐zeolite catalysts were synthesized and tested in hydroconversion of a model compound – methyl palmitate.RESULTSNi2P catalysts were prepared by in situ phosphidation of metallic Ni/Al2O3‐zeolite precursors by PPh3. Mixtures of zeolite (30 wt%) and boehmite were peptized and extruded to obtain the support granules. SAPO‐11, ZSM‐5, ZSM‐22, ZSM‐23 and ZSM‐12 were used as a zeolite component. The catalysts and supports were characterized by a range of physicochemical methods: chemical analysis (ICP‐AES), low‐temperature N2 adsorption, H2‐temperature programmed reduction, NH3‐temperature programmed desorption, Fourier transform infrared spectroscopy of adsorbed CO, X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, and 27Al and 31P magic angle spinning nuclear magnetic resonance. The catalysts were studied in methyl palmitate hydroconversion (one‐stage hydrodeoxygenation‐isomerization‐hydrocracking) in a continuous‐flow fixed bed reactor at 290–340 °C, 2 MPa, H2/feed = 600 Ncm3/cm3 and LHSV = 5.3 h−1. SAPO‐11 containing sample showed high selectivity to C15 and C16 iso‐alkanes (63%, at 340 °C), and all ZSM‐containing samples showed high selectivity to cracked C5–C9 products (55–100%, at 340 °C) with varying amounts of iso‐alkanes (31–57%, at 340 °C).CONCLUSIONThe results show that by choosing the zeolite component of the catalyst it is possible to finely tune product quality in the range from low‐temperature diesel fuel to jet fuel or gasoline. © 2024 Society of Chemical Industry (SCI).

Crystallization kinetics as a tool to fine-tune the catalytic activity of Na-LTA zeolite precursors in the transesterification of glycerol to glycerol carbonate

Glycerol carbonate is a versatile molecule used as a fuel additive and a chemical building block. It is a prominent route for glycerol valorization, improving the biodiesel production chain. This base-catalyzed reaction can be carried out using sodium-type zeolites if accessibility to the basic sites is ensured. Herein, we report a facile strategy to fine-tune the number and access to basic sites of Na-LTA zeolite precursors via monitoring the crystallization kinetics of the microporous material. It is demonstrated that an optimal glycerol to glycerol carbonate conversion is obtained when using the solid obtained at the beginning of the crystallization (90 min at 100 °C of hydrothermal step). Textural and spectroscopy characterization reveals that semicrystalline material presents many basic aluminate anions in a very open structure, allowing facile access to glycerol and propylene carbonate. Moreover, it is shown that this catalyst is stable in four successive reaction cycles and active in different reactions conditions

Tuning RHO Zeolite Crystallization Time and Precursors for Stable and Improved Methanol Conversion to Dimethyl Ether Compared to Conventional Catalysts

Tuning RHO Zeolite Crystallization Time and Precursors for Stable and Improved Methanol Conversion to Dimethyl Ether Compared to Conventional Catalysts

Nonthermal plasma coupled with Mn/N-doped carbon catalysts for highly efficient removal of toluene

In order to ensure the excellent performance of a nonthermal plasma (NTP)-catalysis system, a highly efficient catalyst is generally required. In this study, nitrogen-enriched hollow hybrid carbon (N-C) catalysts were designed, synthesized through facile pyrolysis of a zeolitic imidazolate framework precursor, and used as a support on which to disperse Mn species. Notably, the coupling of NTP with the Mn/N-C catalysts resulted in strong activity. Mn loading of 6 % was found to remove almost all toluene (98 % efficiency) and to have COx selectivity (82.1 %) when the specific energy density (SED) value was 252 J·L−1; when the SED value was 102 J·L−1, the energy yield was 10.6 g·kWh−1. The performances of the developed Mn/N-C catalysts were related to their highly dispersed nature and strong ability to activate oxygen and dissociate O3. Hereafter, the toluene decomposition pathway is described. The present findings demonstrate the potential applications of porous N-C-supported metal oxide catalysts in the removal of volatile organic compounds through a catalyzed NTP process.

The Current Understanding of Mechanistic Pathways in Zeolite Crystallization.

Zeolite catalysts and adsorbents have been an integral part of many commercial processes and are projected to play a significant role in emerging technologies to address the changing energy and environmental landscapes. The ability to rationally design zeolites with tailored properties relies on a fundamental understanding of crystallization pathways to strategically manipulate processes of nucleation and growth. The complexity of zeolite growth media engenders a diversity of crystallization mechanisms that can manifest at different synthesis stages. In this review, we discuss the current understanding of classical and nonclassical pathways associated with the formation of (alumino)silicate zeolites. We begin with a brief overview of zeolite history and seminal advancements, followed by a comprehensive discussion of different classes of zeolite precursors with respect to their methods of assembly and physicochemical properties. The following two sections provide detailed discussions of nucleation and growth pathways wherein we emphasize general trends and highlight specific observations for select zeolite framework types. We then close with conclusions and future outlook to summarize key hypotheses, current knowledge gaps, and potential opportunities to guide zeolite synthesis toward a more exact science.

Enhanced photodynamic therapy efficacy of Ni-doped/oxygen vacancy double-defect Ni-ZnO@C photosensitizer in bacteria-infected wounds based on ROS damage and ATP synthesis inhibition

The use of zinc oxide (ZnO) photosensitizers (PSs)-mediated photodynamic therapy (PDT) against bacterial wound infections is greatly restricted by diminished photocatalytic efficiency caused by the rapid recombination of photogenerated electrons and holes. In this work, ZnO PSs with a Ni-doped/oxygen vacancy and a protective carbon shell were successfully synthesized by calcinating a Ni-doping zeolitic imidazolate framework-8 precursor. The double-defect structure and the carbon-based substrates significantly promoted the efficiency of photogenerated electron–hole pair separation, meanwhile, the 3 % Ni doping endows it with great photocatalytic performance as elucidated by photodegradation assays of methylene blue (MB) and density functional theory (DFT) calculations, reinforcing the generation of reactive oxygen species (ROS) by ZnO and showing obvious advantages in antibacterial properties. As the enhanced photogenerated electron transfer and the ROS damage underwent localized accumulation, the PSs disturbed the bacterial membrane integrity and caused bacterial ATP synthesis inhibition, further leading to bacterial lysis and promoting bacterial deaths. Additionally, the PSs showed outstanding efficacy in eradicating bacterial biofilms. Simultaneously, the significantly enhanced PDT antibacterial performance of the PSs in vivo could initiate wound tissue repair and trigger anti-inflammatory reactions by significantly regulating the expression levels of regeneration- and inflammation-related genes or proteins. Furthermore, the PSs consistently exhibited favorable compatibility both in vitro and in vivo. In summary, this study offers evidence of the remarkably efficient and biologically safe performance of Ni-ZnO@C PSs, with antibacterial properties advancing wound healing, both in controlled laboratory environments and living organisms, further underscoring their substantial potential for biomedical applications.

Carbon nanodots derived from organo-templated zeolites for femtosecond mode-locked fiber laser

Carbon nanodots (CNDs) have been widely investigated due to their physicochemical and optical properties. However, the nonlinear saturable absorption property and its application in laser technology is rarely reported. Here, we report the CNDs as an ideal saturable absorber (SA) for ultra-stable femtosecond mode-locked fiber laser at a wavelength of 1.5 μm. The mono-sized CNDs of 2 nm are fabricated from a dipropylamine-templated zeolite precursor calcination with a temperature of 380 °C. The nonlinear saturable absorption property of the as-synthesized CNDs is investigated by using a balanced twin-detector measurement system. The modulation depth and saturable intensity are measured to be 33 % and 3.1 MW/cm2, respectively. By inputting the CNDs SA into the erbium-doped fiber laser (EDFL) ring cavity, a highly stable mode-locked EDFL with pulse width of 388 fs and single-to-noise ratio (SNR) of 84.4 dB can be obtained. In addition, stable soliton pairs with single-pulse width of 422 fs and SNR of 84.1 dB can also be achieved. These findings demonstrate that the carbon dots can be used as an ideal SA and has promising applications in ultrafast photonics.

In situ preparation of a nickel-oxy-hydroxide decorated ITQ-2 composite: a hydrodeoxygenation catalyst.

A layered zeolite precursor of MWW type (MCM-22) was successfully delaminated (ITQ-2) in situ in the presence of nickel oxy-hydroxide. The broadening of XRD peaks corresponding to the (100), (220), and (310) planes and the disappearance of the (002) plane confirm the delamination. The curled ITQ-2 sheets having uniform lattice fringes, and the slit-shaped layers illustrate the formation of nickel-oxy-hydroxide-decorated ITQ-2 (Ni-ITQ-2 composite). The Ni-ITQ-2 composite is efficient for hydrodeoxygenation (HDO) of m-cresol, with a 99% yield of methylcyclohexane and exhibits excellent hydrotreating abilities for various oxygenated aromatics and cycloalkanes.

Micro-mesoporous ferrierite obtained using the cationic polymer Luviquat and post-synthesis treatment

This study investigated for the first time the synthesis of ferrierite zeolite through the vapor-phase transport method using the cationic polymer Luviquat as a mesopores-generating agent, followed by desilication treatment. The effect of ferrierite's textural and acid properties was then evaluated in the catalytic cracking of ultra-high molecular weight polyethylene (UHMWPE). The synthesized zeolites showed a crystallinity of 91%–100% and similar Si/Al ratios. After the desilication, there was a decrease in these values along with an increase in acidity, attributable to the extraction of structural silicon. The strong interaction between the polymer and the zeolite precursor during the self-assembly process led to the formation of intracrystalline mesoporosity. However, an internal diffusion limit and/or steric hindrance hinders the complete incorporation of the polymer into the ferrierite structure, especially at high polymer concentrations. Thus, the optimal composition was 40% Luviquat, which resulted in twice the volume of mesopores compared to the sample prepared without the polymer. The desilication of the samples synthesized with the Luviquat led to a substantial increase in mesoporosity, ranging from 67% to 183%, relative to microporous ferrierite. The introduction of mesoporosity and the modification of acid properties in ferrierite contributed to a reduction in the temperature for the cracking of UHMWPE, between 66 and 93 °C compared to the pure polymer. However, in all cases, there was an increase in the average apparent activation energy in relation to desilicated microporous ferrierite zeolite, possibly due to changes in product distribution.

Atomically Dispersed Co2 MnN8 Triatomic Sites Anchored in N-Doped Carbon Enabling Efficient Oxygen Reduction Reaction.

Atomically dispersed transition metal-nitrogen/carbon (M-N/C) catalysts have emerged as the most promising substitutes to precious platinum counterparts toward oxygen reduction reaction (ORR). However, the reported M-N/C catalysts are usually in the form of common M-N4 moieties with only one single metal active site and suffer from insufficient activity. Herein, we elaborately developed an unusual trinuclear active structure with nitrogen-coordinated one Mn atom adjacent two Co atoms (Co2 MnN8 ) anchored in N-doped carbon as highly efficient ORR catalyst via adsorption-pyrolysis of bimetallic zeolitic imidazolate framework precursor. Atomic structural investigations and density functional theory (DFT) calculations revealed that Co2 MnN8 would experience a spontaneous OH binding to form Co2 MnN8 -2OH as the real active site, leading to a single electron-filled state in the orbital and an optimized binding energy of intermediates. Accordingly, the as-developed Co2 MnN8 /C exhibited an unprecedented ORR activity with a high half-wave potential of 0.912V and outstanding stability, not only surpassing the Pt/C catalyst but also representing a new record for the Co-based catalyst. This article is protected by copyright. All rights reserved.

Printed flexible supercapacitor from conductive ink of graphite nanocomposite blended with Co3O4 to facilitate the fabrication of energy storage device

An easy-to-make and potential technique for designing of supercapacitor has been proposed by printing conductive ink from porous Co3O4 and graphite nanocomposite. This method simplifies the process of fabrication of energy storage devices. The ink used in this fabrication was prepared after blending the porous Co3O4 nanoparticle composite with graphite, porous Co3O4 nanosphere was synthesized in situ through a single-step calcination process of the zeolitic imidazolate framework precursor (ZIF-67). To ensure homogenous fabrication, the supercapacitor was prepared by screen-printing technology, which allowed for the even distribution of ink using a standard squeeze spreader. The performance was evaluated by designing two types of supercapacitors: an ultra-flexible symmetric supercapacitor (CG-1) and an asymmetric supercapacitor (ASSC), both of which utilized the solid polymeric electrolyte with a resistance of 4.92 Ω. Our research showed an enhanced specific capacitance of 85 Fg−1 for CG-1 and 137 Fg−1 for ASSC, indicating the high efficiency of these lab-created screen-printed supercapacitor devices. The ASSC supercapacitor exhibited remarkable capacitance retention (%). After 2500 cycles, it retained 96.3 %, and even after 5000 cycles, it retained 85.9 %. The results highlight its exceptional flexibility and durability, with a retention rate ranging from 97.8 % to 99.3 % when subjected to various bending angles. Finally, the current works present the fabrication of supercapacitors using a user-friendly screen-printing technique, where ink was prepared by the optimal recipe of ZIFs and graphite nanocomposite. Our approach involved preparing an ink with an optimized recipe of zeolitic imidazolate frameworks (ZIFs) and graphite nanocomposites. It emphasizes the promising prospects of employing metal-organic frameworks, specifically ZIFs, as effective templates for producing porous electrode materials. This breakthrough paves the way for the production of innovative devices and their application in the future of state-of-the-art flexible energy storage.

A simple strategy for synthesis of b-axis-oriented MFI zeolite macro-nanosheets

Zeolite nanosheets with shortened diffusion paths and high external surface areas have drawn significant attention. This unique morphology of zeolites can endow them with reduced diffusion resistance and high accessibility of active sites, and thereby good catalytic performance. Exploring simple synthesis strategies for zeolite nanosheets is mostly desired in zeolite chemistry. Herein, MFI zeolite nanosheets with a thickness of 50-100 nm along the b -axis and a length of 1 μm along the c -axis, namely zeolite macro-nanosheets, have been successfully synthesized via the strategy of combining pre-aging and pH regulation without the use of complex templates/additives and fluorine media. Pre-aging at a relatively high temperature of 90 °C and low alkalinity for crystallization (pH = 7.0~8.5) are found to play key roles in controlling macro-nanosheet synthesis, which can promote the formation of MFI zeolite precursors and then dissociate them into smaller ones for the following oriented aggregation during hydrothermal treatment. Crystallization kinetic studies suggest that the two-dimensional crystal growth is the intrinsic behavior of zeolite crystallization under employed conditions. This synthesis strategy can be easily extended to the synthesis of heteroatom-containing MFI macro-nanosheets, such as ZSM-5 and TS-1.

Amine-grafted H-MFI zeolite precursors as acidic-basic catalysts for deacetalization-Knoevenagel condensation

Amorphous and semi-crystalline precursors of zeolites have a large number of silanols that can be used to anchor organic functionalities, like silane-based amines, resulting in formation of basic sites. This work describes the use of amorphous and semi-crystalline precursors of H-MFI zeolite reacting with aminopropyltrimethoxysilane (APTMS) to produce bifunctional acidic-basic catalysts for the deacetalization-Knoevenagel condensation. The effect of precursors crystallinity on the catalytic performance is explained by the formation of Brønsted acidic sites, which catalyze the deacetalization step, and on the propylamine anchoring capacity, controlled by the amount of external silanols present in the aluminosilicate. It is shown that the aluminosilicates with lower crystallinity provide a higher yield of the end product ethyl trans-α-cyanocinnamate due to the greater number of grafted propylamine groups. These results provide new insights into the preparation of acidic-basic catalysts for converting bulky molecules.

Design of catalysts with controlled porosity and variable acidity for the synthesis of industrialized products

By using nanotechnology and the versatility in the micro-mesoporous solids synthesis, it was possible to design and synthesize catalysts with custom-controlled acidity. Aluminum or boron modified MCM-41 type nanocatalysts (Si/metal = 20) were synthesized by “conventional way” showed a very weak and moderate Brønsted acidity, respectively, caused by the formation of nest silanols due the incorporation of the heteroatom. Aluminosilicates were also synthesized by “zeolitic precursors assembly way” and the presence of these zeolitic domains caused a greater acidic strength. Thus, this development of catalysts with active sites within range of acid strength allows manage the synthesis of different industrial interest compounds.

Mini Review on Synthesis, Characterization, and Application of Zeolite@MOF Composite

Zeolite@MOF composite is a bifunctional composite formed from thermal and structural stable inorganic zeolite and high tunable surface area and structural flexible MOF. The parent material “MOF” has a higher surface area and structural elasticity than zeolite. Nevertheless, MOF is more structurally and mechanically unstable than zeolite. Thus, compositing of structural stable zeolite with tunable porous MOF has enhanced the applications of Zeolite@MOFcomposite over its parent materials. The Zeolite@MOF composite was synthesized through the hydrothermal method, the solvothermal method, the refluxing method, and the microwave-assisted method. The synthesized Zeolite@MOF composite also further modified via postsynthesis or presynthesis modification method to bring them extra functionality. Recently, researchers have synthesized Zeolite@MOF composite using hydrothermal method for zeolite crystallization and then solvothermal growth of MOF over presynthesized zeolite surface to reduce competitions between zeolite and MOF precursors through nucleation and crystal formation. The structure of Zeolite@MOF composite, such as morphology, microstructure, functional group, particle size, elemental composition, and weight loss was also analysed using SEM, TEM, FTIR, X-RD, EDX, and TAG, respectively. After exploring the characterization techniques of Zeolite@MOF composite, a performance application of Zeolite@MOF was also reviewed. Zeolite@MOF is used for the degradation of organic dyes (methyl blue and methyl orange) from wastewater; zeolite@MOF is also used as a catalyst in the synthesis of organic compounds. Zeolite@MOF composites showed higher catalytic activity, high selectivity, and high product yield than the corresponding zeolite and MOF parent materials. Hence, the compositing of zeolite and MOF is promising to overcome the individual limitations of zeolite and MOF. Zeolite@MOF composite has a synergic performance advantage over its parent materials.

Does Water Enable Porosity in Aluminosilicate Zeolites? Porous Frameworks versus Dense Minerals.

Recently identified zeolite precursors consisting of concentrated, hyposolvated homogeneous alkalisilicate liquids, hydrated silicate ionic liquids (HSIL), minimize correlation of synthesis variables and enable one to isolate and examine the impact of complex parameters such as water content on zeolite crystallization. HSIL are highly concentrated, homogeneous liquids containing water as a reactant rather than bulk solvent. This simplifies elucidation of the role of water during zeolite synthesis. Hydrothermal treatment at 170 °C of Al-doped potassium HSIL with chemical composition 0.5SiO2:1KOH:xH2O:0.013Al2O3 yields porous merlinoite (MER) zeolite when H2O/KOH exceeds 4 and dense, anhydrous megakalsilite when H2O/KOH is lower. Solid phase products and precursor liquids were fully characterized using XRD, SEM, NMR, TGA, and ICP analysis. Phase selectivity is discussed in terms of cation hydration as the mechanism, allowing a spatial cation arrangement enabling the formation of pores. Under water deficient conditions, the entropic penalty of cation hydration in the solid is large and cations need to be entirely coordinated by framework oxygens, leading to dense, anhydrous networks. Hence, the water activity in the synthesis medium and the affinity of a cation to either coordinate to water or to aluminosilicate decides whether a porous, hydrated, or a dense, anhydrous framework is formed.

Effects of Curing Temperature and Water Glass Modulus on the Preparation of Hierarchical Zeolite Precursors

Effects of Curing Temperature and Water Glass Modulus on the Preparation of Hierarchical Zeolite Precursors