Nano-sized ZSM-5 Research Articles

Facile synthesis and mechanistic insights into ZSM-5 aggregates via a mesoporogen-free route

Developing hierarchical zeolites is highly important for catalytic applications. In this study, micro- and submicron-sized hierarchical ZSM-5 zeolites, composed of aggregated nanosized ZSM-5 crystals, were facilely synthesized without any mesoporogen. The effects of the gel composition in a mesoporogen-free system on the formation of ZSM-5 aggregates were studied. The results revealed that the Na2O/SiO2 molar ratio and the aluminum source exerted significant impacts. Furthermore, we demonstrated that the morphology and size of the ZSM-5 aggregate could be easily adjusted by varying the gel composition. Mechanistic insights indicated that the formation of hierarchical ZSM-5 aggregates in the mesoporogen-free system likely followed a space-confined growth mechanism.

Enhancing the catalytic performance of H-ZSM-5 in bio n-butanol dehydration by zeolite crystal engineering

NH4F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5’s, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH4F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes.

Disinfectant-Assisted Preparation of Hierarchical ZSM-5 Zeolite with Excellent Catalytic Stabilities in Propane Aromatization.

A series of quaternary ammonium or phosphonium salts were applied as zeolite growth modifiers in the synthesis of hierarchical ZSM-5 zeolite. The results showed that the use of methyltriphenylphosphonium bromide (MTBBP) could yield nano-sized hierarchical ZSM-5 zeolite with a "rice crust" morphology feature, which demonstrates a better catalytic performance than other disinfect candidates. It was confirmed that the addition of MTBBP did not cause discernable adverse effects on the microstructures or acidities of ZSM-5, but it led to the creation of abundant meso- to marco- pores as a result of aligned tiny particle aggregations. Moreover, the generation of the special morphology was believed to be a result of the coordination and competition between MTBBP and Na+ cations. The as-synthesized hierarchical zeolite was loaded with Zn and utilized in the propane aromatization reaction, which displayed a prolonged lifetime (1430 min vs. 290 min compared with conventional ZSM-5) and an enhanced total turnover number that is four folds of the traditional one, owing to the attenuated hydride transfer reaction and slow coking rate. This work provides a new method to alter the morphological properties of zeolites with low-cost disinfectants, which is of great potential for industrial applications.

Nonionic polymer and amino acid-assisted synthesis of ZSM-5 nanocrystals and their catalytic application in the alkylation of 2-methylnaphthalene.

The synthesis of nanosized ZSM-5 zeolites with high crystallinity and suitable acidity is very significant for their great potential in various catalytic applications. Herein, a series of zeolite ZSM-5 crystals with different particle sizes and SiO2/Al2O3 ratios (10-30) were synthesized by a temperature-varying two-step crystallization method in a concentrated gel system containing L-lysine and/or polyvinylpyrrolidone (PVP) additives. By optimizing the addition amounts of the two additives, the crystal size of the ZSM-5 zeolite could be reduced to less than 100 nm. Meanwhile, relatively high crystallinity and framework Al incorporation rates could be achieved, resulting in the generation of high-quality ZSM-5 nanocrystals. The nanosized H-form ZSM-5 zeolite with a SiO2/Al2O3 ratio of 20 showed enhanced catalytic efficiency and stability for the alkylation of 2-methylnaphthalene (2-MN) with methanol to produce an important intermediate, 2,6-dimethylnaphthalene (2,6-DMN). A relatively high and steady yield of 2,6-DMN (above 7.2%) could be achieved during 20 h time-on-stream at 400 °C. The smaller crystal size, higher crystallinity and framework Al content could provide more accessible Brønsted acid sites in the 10-membered ring channel of the ZSM-5 nanocrystals, which are the main active sites responsible for the shape-selectivity of the targeted product of 2,6-DMN. As a result, the formation of other side products like 1-MN and poly-MN could be effectively inhibited, thus leading to an improved 2,6-DMN yield and coke resistance over the nanosized ZSM-5 catalyst.

Friedel-Crafts Acylation of Aromatics with Acetic Anhydrideover Nano-Sized Rare Earth Cation Exchanged ZSM-5 Catalysts

Friedel-crafts acylation of aromatic compounds used to synthesize aromatic ketones and significance has commercial importance in diverse areas of fine chemical synthesis and pharmaceutical manufacturing industry. Conventionally, acylation reactions are catalysed by corrosive metal halides or mineral acids. The present work reports on the catalytic activity of nanocrystalline ZSM-5 and rare earth metal cation such as La3+, Ce3+ and Nd3+ exchanged ZSM-5 in the liquid phase acylation of veratrole with acetic anhydride. The catalyst was thoroughly characterized for its structure. The nanocrystalline Ce-ZSM-5 displayed highest activity towards the acylation of veratrole. The catalytic performance of Ce-ZSM-5 was used to compare its activity for the acylation of other aromatics; such as toluene, anisole and veratrole. The nanocrystalline Ce-ZSM-5 shows highest activity over nanocrystalline ZSM-5 in acylation reactions of aromatics. It was established that smaller size crystal of Ce-ZSM-5showed superior activity, which is due to the enhanced density of acidic sites along with increased external surface area of smaller crystal which facilitate the activity of the acylation reaction. The catalysts used in this study are reusable without any loss of activity.

Effects of different phosphorus modification methods on acid and catalytic properties of nano-sized ZSM-5 zeolite in toluene alkylation with methanol

Effects of different phosphorus modification methods on acid and catalytic properties of nano-sized ZSM-5 zeolite in toluene alkylation with methanol

Core-shell SAPO-34@ZSM-5 composite via in situ solid-solid transformation of pre-coating MCM-41 shell and its application in methanol-to-olefins

Hierarchically core-shell-structured SAPO-34@ZSM-5 composite zeolite was successfully achieved by an in situ solid-solid transformation of a pre-coating MCM-41 shell layer with the help of ZSM-5 seeds under a traditional hydrothermal crystallization route. As a result, a uniform nano-sized polycrystalline ZSM-5 shell closely grows on the core SAPO-34 microsphere, thus forming a desirable core-shell structured zeolite composite. Besides, the SAPO-34 core and the polycrystalline ZSM-5 shell are intimately connected through mesosilica substrates as a “bridge” which guarantees the integrity of the core-shell structure very well, even under harsh ultrasonic treatment at a high frequency. More crucially, this innovative method effectively overcomes the chemical and structural incompatibility between the core crystals and the shell zeolite during synthesis, and simultaneously avoids the collapse and dissolution of SAPO-34 crystals mainly derived from the shielding effect of MCM-41 shell layer under a highly alkaline gel precursor yielding ZSM-5. Furthermore, the methanol-to-olefins (MTO) was selected as a probe reaction so as to investigate the catalytic performance of the core-shell SAPO-34@ZSM-5. It is found that besides obtaining high light olefins yield (12.3% more than that on the reference catalyst), the catalytic lifetime over core-shell SAPO-34@ZSM-5 catalyst is greatly improved, about 3 times as long as that over the pristine SAPO-34 and 2.6 times as long as that on the corresponding physically-blended SAPO-34+ZSM-5. The superior catalytic performances on the core-shell SAPO-34@ZSM-5 can be attributed to the synergetic effects between SAPO-34 (core) and ZSM-5 (shell) including different framework structures, moderate acidic properties, and well-defined hierarchical architectures.

Direct synthesis of Al-rich ZSM-5 nanocrystals with improved catalytic performance in aromatics formation from methane and methanol

Nanosized ZSM-5 (<100 nm) zeolites with high acidity (Si/Al < 15) can bring distinct advantages as catalysts for obtaining aromatics in C1 chemistry. Synthesis of such nanosized zeolites in a cheap and scalable manner remains a challenge. Herein, nanosized ZSM-5 (20–50 nm) with high acidity (Si/Al = 11) was hydrothermally synthesized in high yield using p-phenylenedimethylene-bis(tripropylammonium) dichloride (Pr3N-benzyl-NPr3) as the sole organic structure-directing agent (OSDA). By investigating the solid products formed during zeolite synthesis, it was found that crystallization follows a solid-state transformation mechanism. An in-depth NMR study combined with TGA measurements reveals that, after early electrostatic interaction between condensed aluminosilicate and the ammonium groups of OSDA, ZSM-5 crystallizes around the OSDA. Owing to its high acidity and shortened diffusion paths, such nanosized ZSM-5 demonstrates, compared to bulk ZSM-5, enhanced aromatics formation in methanol dehydration and non-oxidative dehydroaromatization of methane reactions.

Rational Design of Bimetal Mn-Ce Nanosheets Anchored on Porous Nano-sized ZSM-5 Zeolite for Adsorption-Enhanced Catalytic Oxidation of Toluene

Catalytic oxidation is one of the most promising methods to remove toluene; manganese-cerium catalysts have high activity in the catalytic oxidation of toluene. Herein, nano-sized ZSM-5 was synthesized using a simple hydrothermal method, and catalysts with different Mn and Ce contents were prepared via alcohol-induced redox precipitation at room temperature. In addition, zeolite provides sufficient surface area for the dispersion of manganese cerium catalysts and plays a role in concentration and enrichment in the catalytic conversion of toluene. Based on the experimental characterization results, the 20Ce/M1Z1 catalyst exhibited the best catalytic activity, achieving 90% toluene conversion at 215 °C. Moreover, the catalyst still has excellent catalytic activity in humid environments. This work provides a new strategy to expose more active sites and enhance toluene adsorption, which provides a reference for the development of more efficient catalysts in the future.

Effect of ZSM-5 Particle Size and Framework Silica-to-Alumina Ratio on Hexane Aromatization

Parent ZSM-5 and Ga-modified ZSM-5 catalysts with different Si/Al ratios and particle sizes were prepared. The physicochemical properties of the prepared catalysts were investigated by performing X-ray powder diffraction analysis, BET surface area analysis, and NH&lt;sub&gt;3&lt;/sub&gt;-TPD analysis. The performance of the aromatization reaction of the prepared catalysts was evaluated with 1-hexane as a model compound. The zeolite catalysts with a low SiO&lt;sub&gt;2&lt;/sub&gt;/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ratio possessed better activity than those with a high SiO&lt;sub&gt;2&lt;/sub&gt;/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ratio. Ga modification significantly improved the catalyst aromatization selectivity. Through aromatization, the acid sites of Ga-modified nano-sized zeolites promoted the selective conversion of produced olefin to aromatics by removing H-atoms. For the parent ZSM-5 and Ga-modified catalysts, the catalyst stability increased with an increase in the SiO&lt;sub&gt;2&lt;/sub&gt;/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; molar ratio. The nano-sized ZSM-5 catalyst with a high SiO&lt;sub&gt;2&lt;/sub&gt;/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ratio exhibited better catalytic stability than the microscale ZSM-5, and the nano-sized catalyst with a low SiO&lt;sub&gt;2&lt;/sub&gt;/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ratio showed very low stability.

Selective production of aromatics from catalytic pyrolysis of biomass wastes: Effects of feedstock properties and key oxygenated intermediates on aromatics formation

The catalytic pyrolysis is a promising method for obtaining value-added aromatics, especially benzene, toluene and xylene (BTX). For different biomass-based materials, the dual catalyst system composed of CaO-based and ZSM-5-based catalysts showed an obvious selectivity for the BTX production. This study chose CaO derived from organic calcium precursors (Org-CaO) and nano-sized ZSM-5 (NZSM-5), and comprehensively investigated the effects mechanism of biomass components on the formation pathways of BTX via Py-GC/MS. Under the catalysis of NZSM-5, the BTX yields were only 7.8–30%. The BTX yields on Org-CaO/NZSM-5 were as follows: lipid (63.1%) > hemicellulose (55.4%) > cellulose (40.2%) > lignin (21.7%). Typical pyrolysis intermediates were employed to quantitatively reveal the intermediate reactions. Pyrolysis intermediates exhibited low BTX-forming reactivity over NZSM-5. The pre-catalysis of Org-CaO selectively converted part undesired intermediates (fatty acids and furans) into BTX precursors (short-chain olefins and ketones), facilitating the remarkable increase of BTX yield in the subsequent NZSM-5 catalysis process. However, the pre-catalysis of Org-CaO can hardly make the ring opening reaction of lignin-derived phenolic compounds that have very low reactivity on NZSM-5, and thence high-lignin biomass obtained low BTX production during catalytic pyrolysis by Org-CaO/NZSM-5. These findings afforded a new route for increasing the BTX yields by directionally forming BTX precursors or controlling biomass components.

ZSM-5 nanocrystal promoted low-temperature activity of supported manganese oxides for catalytic oxidation of toluene

• Nano-sized ZSM-5 zeolite was prepared by amino acid assisted method. • Effect of the support size on the formation of MnO x species was studied. • Small-sized ZSM-5 can highly disperse active MnO x species. • Abundant oxygen vacancies are formed on the MnO x supported by small-sized ZSM-5. • MnO x /Z5-L 0.2 shows excellent low-temperature activity in toluene combustion reaction. Nanoscale zeolites are of great practical interest due to their advantages of favorable mass transfer, accessibility to active sites, and large external surface area. Herein, ZSM-5 ( MFI -type) nano-sized zeolites were prepared by conventional hydrothermal and amino acid-assisted approaches to support MnO x species. The morphology, acidity, textural properties, and chemical state of the prepared MnO x /ZSM-5 samples are comprehensively characterized. The size effect of ZSM-5 nanocrystals on the physicochemical properties of supported MnO x species and on their catalytic oxidation behavior for the combustion of toluene is investigated. Beneficially from the larger surface area and smaller crystal size, the smaller-sized ZSM-5 zeolite (Z5-L 0.2 , ∼100 nm) prepared by the amino acid-assisted method can highly disperse more active MnO x species than the larger ZSM-5 counterpart (∼500 nm). Owing to abundant surface oxygen vacancies and surface adsorbed oxygen, as well as superior low-temperature reducibility, the MnO x supported on nanosized Z5-L 0.2 zeolites exhibits remarkably enhanced low-temperature activity for the catalytic oxidation of toluene.

Preparation of Ga Isomorphic Substituted Ultrafine Nanosized ZSM-5 Zeolite and Its Catalytic Performance for MTG Reaction

Preparation of Ga Isomorphic Substituted Ultrafine Nanosized ZSM-5 Zeolite and Its Catalytic Performance for MTG Reaction

One Step Dimethyl Ether (DME) Synthesis from CO2 Hydrogenation over Hybrid Catalysts Containing Cu/ZnO/Al2O3 and Nano-Sized Hollow ZSM-5 Zeolites

The study has focused on the development of bifunctional catalytic materials for the direct DME synthesis from CO2/H2. The industrial Cu/ZnO/Al2O3 is used as the copper based catalyst for the first step of the methanol synthesis from CO2/H2. It will be combined with hollow nano-ZSM-5 zeolites with mesoporous shell as the acid catalyst of the second step the methanol dehydration to DME. The bifunctional materials will be tested in the direct DME synthesis from CO2/H2 under the following conditions: T = 225 °C, p = 30 bar, H2/CO2 = 3. Under our reaction conditions, CO was not observed, only the DME majority product (77.5%) and CH3OH (22.5%) were obtained.

Rapid solvent-free synthesis of nano-sized ZSM-5 with a low Si/Al ratio at 90 °C

A liquid seed containing tremendous amounts of four- and five-membered silicon rings boosts the ZSM-5 crystallization and Al incorporation into the framework.

Hierarchical zeolites obtained by alkaline treatment for enhanced n-pentane catalytic cracking

This study manufactured various hierarchical ZSM-5 zeolites using NaOH, NaAlO2, Na2CO3, K2CO3 and NaHCO3 solutions through post-treatment. Later, X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray fluorescence (XRF), N2 adsorption and desorption, solid state 29Si and 27Al MAS NMR, ammonia temperature programmed desorption (NH3-TPD) as well as pyridine adsorption infrared spectra (Py-FTIR) were carried out to characterize their structure properties and acidities. Further, this study investigated n-pentane catalytic cracking for producing the light olefins over hierarchical nano-sized ZSM-5 zeolites. Alkaline treatment with milder NaHCO3 was much more controllable and reasonable than treatment with other alkalis, which not only adjusted the acidity to promote n-pentane activation, but also formed hierarchical structures combing micropores and mesopores to reduce diffusion resistance and suppress secondary reaction contributing to an enhanced catalytic ability and anti-coke deposition performance. Among the catalysts, ZNaHCO3 exhibited ∼92% the highest n-pentane conversion and ∼50% light olefins selectivity during n-pentane catalytic cracking under 590 °C for 300 min, simultaneously, and these figures markedly increased relative to those for the parent ZSM-5 zeolite. Most importantly, it was also proved that HTC values are relevant to the degree of effectiveness of NaHCO3 desilication, and that mesopore formation contributes to the desirable selectivity of light olefins and coke amount.

Aromatization mechanism of coupling reaction of light alkanes with CO over acidic zeolites: Cyclopentenones as key intermediates

The aromatization of light alkanes (C4-C6) is an important value-added reaction. However, the yield of aromatics is always limited by the simultaneous generation of small alkanes (CH4 and C2H6) due to H/C balance. Herein, we demonstrate that the introduction of CO into light alkanes over zeolites significantly enhanced aromatic selectivity and an aromatics selectivity of 85% was achieved in the case of cyclopentane and CO coupling reaction over H-ZSM-5. Methyl-substituted cyclopentenones were observed and considered as the most important intermediates for aromatics formation. Multiple characterizations revealed the coupling mechanism: (1) CO inserts into carbenium ions to form acylium cations, (2) acylium cations react with olefins to generate unsaturated ketones, (3) unsaturated ketones cyclize to methyl-substituted cyclopentenones, (4) methyl-substituted cyclopentenones convert to monocytic aromatics. Methyl-substituted indanones were also discovered causing the generation of binuclear aromatics, such as naphthalene. Nano-sized ZSM-5 and TEOS modifications were applied to enhance the BTX selectivity.

Quaternary ammonium cellulose promoted synthesis of hollow nano-sized ZSM-5 zeolite as stable catalyst for benzene alkylation with ethanol

Catalytic alkylation of benzene with ethanol has been considered as a sustainable alternative for producing ethylbenzene/diethylbenzene. This paper reports the promoted synthesis of hollow nano-sized (20–80 nm) ZSM-5 zeolite as excellent yet durable catalyst of benzene alkylation, which is achieved by adding N-methyl-2-pyrrolidone (NMP) and quaternary ammonium cationic hydroxyethyl cellulose (JR-400) in its synthesis gel during the synthesis. It is revealed by the ESI–MS and TEM characterization that the NMP promotes the dissolution–recrystallization of the ZSM-5 and a hollow structure is generated during the process. The JR-400 as special promoter further favors the formation of ordered nano-zeolite grain and suitable microstructure, confirmed by the molecular dynamic modeling and characterization. That action corporately contributed to the hollow nano-sized ZSM-5 zeolite that provided hierarchical porous structure and mild acid centers, as evidenced by the 129Xe and 1H NMR spectra. The obtained hollow zeolite ZSM-5 then exhibits enhanced catalytic activities and selectivity for benzene alkylation. Moreover, it also displays an extremely superior stability (deactivation rate constant, −0.06%/h) in the catalysis of benzene alkylation with ethanol. This behavior is attributed to its hierarchical porous structure (namely less diffusion resistance) and mild acid centers, which is beneficial to moderate the carbon deposition and then the catalyst deactivation. Those research results urge the JR-400-promoted synthesis as a facile strategy for the hollow nano-sized ZSM-5 with enhanced catalytic performance during the benzene alkylation with the ethanol.

Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio.

Zeolite crystals offering a short diffusion pathway through the pore network are highly desired for a number of catalytic and molecule separation applications. Herein, we develop a simple synthetic strategy toward reducing the thickness along the b-axis of MFI-type crystals, thus providing a short diffusion path along the straight channel. Our approach combines preliminary aging and a fluoride-assisted low-temperature crystallization. The synthesized MFI crystals are in the micrometer-size range along the a- and c-axis, while the thickness along the b-axis is a few tens of nanometers. The synthesis parameters controlling the formation of platelike zeolite are studied, and the factors controlling the zeolite growth are identified. The synthesis strategy works equally well with all-silica MFI (silicalite-1) and its Al- and Ga-containing derivatives. The catalytic activity of platelike ZSM-5 in the methanol-to-hydrocarbons (MTH) reaction is compared with a commercial nanosized ZSM-5 sample, as the platelike ZSM-5 exhibits a substantially extended lifetime. The synthesis of platelike MFI crystals is successfully scaled up to a kilogram scale.

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.