Hierarchical Mordenite Research Articles

Soft-templating synthesis of hierarchical mordenite as high-performance catalyst for cyclic acetals production via acetylation of glycerol and benzaldehyde

Highly active hierarchical mordenite zeolite with micro/mesoporosity (TM-n) for selective synthesis of cyclic acetals via acetylation reaction is reported. The hierarchical zeolite is synthesized using soft-templating approach with variations in octadecyltrimethoxysilane (OTMS/Al2O3 ratio, n = 0.2, 0.3 and 0.4) in precursor hydrogels. The results reveal that OTMS not only creates secondary mesoporosity in zeolite framework (larger mesopore volume, external surface area, average pore diameter), but also influences the crystallization process, altering the crystal morphology, crystallinity and Si/Al ratios. Among TM-n zeolites prepared, TM-0.3 hierarchical mordenite has the optimum OTMS amount incorporated while further increasing the OTMS amount leads to the formation of ANA/GIS intergrowth. Thanks to the accessible hierarchical porosity, reduced acidity and morphological effects, the TM-0.3 hierarchical mordenite exhibits excellent catalytic performance (84.1% conversion, TOF = 0.087 s−1, 61.5% dioxolane selectivity) in acetylation of glycerol and benzaldehyde (160 °C, 20 min) better than pristine mordenite. The catalyst is reusable for five runs with minimal loss of activity (TOF = 0.087 → 0.084 s−1), making it a promising catalyst for chemical productions involving bulky molecules. In addition, comparative catalytic tests with classical homogeneous and heterogeneous catalysts, including H2SO4, HCl, CH3COOH, H–Y, H-LTL, Na-X, Na-A, were performed.

Synthesis of hierarchical mordenite by solvent-free method for dimethyl ether carbonylation reaction.

A series of hierarchical mordenite (MOR) catalysts were synthesized by adding soft templates via the solvent-free method. The influence of different kinds of soft templates on the structure, morphology and acid sites of mordenite were systematically characterized. The characterization results revealed that the addition of soft templates could successfully introduce hierarchical structure into the system while maintaining good crystallinity. The specific surface area and pore volume became larger. Surfactants could also affect the amount and distribution of acid sites, which in turn would affect the dimethyl ether carbonylation activity. Compared with cationic and nonionic surfactants, the addition of anionic surfactants such as sodium dodecyl benzene sulfonate could result in more Al species to preferentially enter into the 8 member ring, thus enhancing the amount of active sites for the carbonylation reaction while weakening the strength. Meanwhile, the addition of sodium dodecyl benzene sulfonate could also reduce the number of strong acid sites in the 12 member ring and obviously improve the carbonylation performance.

Post-synthetically modified hierarchical Mordenite and ZSM-5 zeolite and their catalytic performances in benzylation of acetic acid to benzyl acetate

Post-synthetically modified hierarchical Mordenite and ZSM-5 zeolite and their catalytic performances in benzylation of acetic acid to benzyl acetate

Liquid-phase benzylation of toluene by benzyl alcohol over micro-mesoporous hierarchical mordenite zeolite.

In this work, post-synthetic effective acid (HNO3) and base (NaOH) etching technique are used to create hierarchical mordenite having different pore structure. The powder X-ray diffraction (P-XRD) technique was used to confirm the crystalline structure of the base-modified and acid-modified mordenite. Field emission-scanning electron microscope (FE-SEM) was employed to confirm the structural morphology of the materials. The modified mordenite was further characterised by inductive coupled plasma-optical emission spectrometry (ICP-OES), N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), and acid-base titration, to confirm the structural integrity, presence of active acidic sites, and other vital parameters. The structure was well conserved after the change, as evidenced by the characterisation. The toluene benzylation with benzyl alcohol using hierarchical mordenite and H-mordenite produced mono-benzylated toluene. Comparison between acid treated, base treated, and H-mordenite was done. All samples were catalytically active as proved by the catalytic result in the benzylation reaction. The results show that the base alteration dramatically enhances the mesoporous surface area of H-mordenite. Furthermore, the acid-treated mordenite had the highest benzyl alcohol conversion (75%), but the base-modified mordenite had benzyl alcohol conversion of 73% with the highest mono-benzylated toluene selectivity (61%). The process was further optimised by varying the reaction temperature, duration, and catalyst quantity. Gas chromatography (GC) was used to evaluate the reaction products and gas chromatography-mass spectrometry (GC-MS) was used to confirm them. Introduction of mesoporosity in the microporous mordenite was found to have significant effect on their catalytic activity.

Synthesis of Hierarchical MOR-Type Zeolites with Improved Catalytic Properties.

Hierarchical MOR-type zeolites were synthesized in the presence of hexadecyltrimethylammonium bromide (CTAB) as a porogen agent. XRD proved that the concentration of CTAB in the synthesis medium plays an essential role in forming pure hierarchical MOR-type material. Above a CTAB concentration of 0.04 mol·L−1, amorphous materials are observed. These hierarchical mordenite possess a higher porous volume compared to its counterpart conventional micrometer crystals. Nitrogen sorption showed the presence of mesoporosity for all mordenite samples synthesized in the presence of CTAB. The creation of mesopores due to the presence of CTAB in the synthesis medium does not occur at the expense of zeolite micropores. In addition, mesoporous volume and BET surface seem to increase upon the increase of CTAB concentration in the synthesis medium. The Si/Al ratio of the zeolite framework can be increased from 5.5 to 9.1 by halving the aluminum content present in the synthesis gel. These synthesized hierarchical MOR-type zeolites possess an improved catalytic activity for n-hexane cracking compared to large zeolite crystals obtained in the absence of CTAB.

Recent Progress in Synthesis and Application of Nanosized and Hierarchical Mordenite—A Short Review

Zeolites with their unique properties find applications in various fields, including medicine, agronomy, ecology, production of detergents and drying agents, and in a number of industrial processes. Among zeolites, mordenite is particularly widespread because of its high silica/alumina ratio, which allows it to resist exposure to high temperatures and to acidic gases and liquids. Mordenite is commercially available as a natural mineral and as a synthesized material. This zeolite is mostly used in its synthetic form as an acid catalyst in the petrochemical industry for the isomerization of alkanes and aromatics. In this review, we consider the scientific literature on the structure, synthesis, and two main types of modifications that solve the diffusion difficulties during catalytic processes. The first type of modifications is related to a reduction of the size of the mordenite crystals obtained to submicron or nanometric range, whereas the second ones aim to obtain hierarchical mordenite samples by appropriate post-synthetic treatments. Both types of modifications find many other applications besides solving diffusion constraints in catalytic processes. Attempts to fine-tune and control the particle size in the first type of modifications or the pore size in the second ones by adjusting various parameters during the synthesis are described.

Recent Progress in Synthesis and Application of Nanosized and Hierarchical Mordenite—A Short Review

Recent Progress in Synthesis and Application of Nanosized and Hierarchical Mordenite—A Short Review

Effect of Pore Connectivity of Pore-Opened Hierarchical MOR Zeolites on Catalytic Behaviors and Coke Formation in Ethanol Dehydration.

The hierarchical zeolite is one of the most promising materials for catalytic applications. However, the effect of its pore connectivity on catalytic behaviors and coke formation has not clearly been revealed. In this contribution, we demonstrate the visualization of the mesopore architecture in three-dimensional perspectives together with the pore connectivity network of pore-opened hierarchical mordenite (MOR), fabricated by the seed-assisted template-free synthesis followed by the fluoride treatment via the electron tomography (ET) technique. Interestingly, the pore-opened zeolites clearly display higher catalytic performance (approximately 80% of ethylene yield) in ethanol dehydration with respect to the parent one due to their additional pore-opened structures connected to the external surfaces of zeolites. In addition, the effect of pore connectivity network on the coke location and type obtained from ethanol conversion has been observed. It was found that the porous structure of the etched sample is directly connected to the external surface, and then, the large area of crystals can contribute to the reaction. Conversely, only a small amount of closed mesopores is observed inside the crystals in the case of the untreated sample, and therefore, the molecules cannot easily penetrate inside crystals for the catalytic reaction. These results open up promising perspectives for the development of hierarchical catalysts including fabrication by the template-free synthesis approach, pore-architecture characterization, and catalytic applications.

Fast synthesis of hierarchical mordenite templated by nanocrystalline cellulose for isomerization of α-Pinene

Mordenite molecular sieves were employed for the isomerization of α-pinene to produce limonene and camphene. To decrease diffusion resistance of α-pinene molecules, nanocrystalline cellulose (NCC) was employed as the mesoporous filler to prepare hierarchical mordenite within 6 h under microwave radiation. NCC crystals present as a rod-like morphology twining around crystals and interact with Al(OH)xOy and Si(OH)xOy species. Stronger interaction with Al(OH)xOy species inhibits the incorporation of aluminum into zeolitic framework. The acidity decreases due to a lower surface Si/Al ratio. Besides creating mesopores and macropores, NCC inhibits the growth or assembly of crystals in the short transverse direction of particles. Compared to mordenite without NCC, conversion increases by ∼50 % and the total yields of camphene and limonene are ∼52 % using mordenite catalysts with NCC. It indicates that macro/mesopores enhance the diffusion of α-pinene in mordenites, increase the accessibility of α-pinene with acid sites. After 5-times cycle tests, the conversion decreases from 63 % to 43 % due to the destruction of zeolitic structure during thermal treatment. In this study, a green synthesis route templated with NCC and green application in isomerization of α-pinene are proposed. These results are important for the synthesis of zeolites using biomass templates rapidly for biomass conversion process.

Enhanced activity and stability over hierarchical porous mordenite (MOR) for carbonylation of dimethyl ether: Influence of mesopores

The dimethyl ether (DME) carbonylation reaction over mordenite is greatly affected by the mass transfer process. In this research, hierarchical mordenite catalysts were synthesized and characterized to investigate the influence of mesopores on the structure, mass transfer and catalytic performance. The results show that the medium-strong acid sites decrease while strong acid sites increase over the hierarchical samples. The introduced mesopores can significantly improve the mass transfer efficiency and the carbonylation performances are markedly improved on the hierarchical samples. In addition, the polymerization degree of coke deposition on the deactivated samples decreases although the coke amount increases. Excessive usage of mesopore templates can damage the structure of the MOR catalysts, thus leading to the loss of acid sites and the decrease in catalytic performance.

Improved Catalytic Performance in Dimethyl Ether Carbonylation over Hierarchical Mordenite by Enhancing Mass Transfer

Dimethyl ether (DME) carbonylation over mordenite (MOR) is a typical spatial confined reaction, but the superior shape selectivity is accompanied by a diffusion limitation of the microporous channel. Thus, enhancing mass transfer to improve the catalytic performance of MOR is important for its application. In this study, an unbiased chemical etching with a NH4F solution was employed to introduce secondary porosity into MOR. Through altering the etching temperature, a series of hierarchical MOR with different porosities were successfully prepared. XRD, Ar adsorption, and ICP together with the quantification of acid sites confirmed that the microporous structure and acidity of pristine zeolite were preserved after etching. The Weisz–Prater criterion was used to assess the internal diffusion limitation of DME and methyl acetate (MA). Moreover, toluene was chosen as a representative molecule in zero length column measurements, in order to explore the mass transfer of coke precursors in pristine and modified MOR. Combining the catalytic performance (i.e., TOFMA, selectivity, and deactivation rate constant) and diffusivity of molecules within MOR, we obtain insight into the influence of diffusion on zeolite-catalyzed DME carbonylation.

Adsorptive properties in toluene removal over hierarchical zeolites

Three kinds of hierarchical Mordenite Framework Inverted (MFI)-type nanozeolites including Si-MFI, Al-MFI and Ti-MFI were successfully synthesized by two-stage varying temperature hydrothermal treatment. Taking toluene as the probe molecule, a series of methods were used to evaluate the adsorption properties of as-synthesized hierarchical zeolites samples including the adsorption breakthrough curves, simulation of adsorption isotherms as well as kinetics models and toluene-TPD (the temperature programmed desorption of toluene). The dynamic adsorption results showed that Al-MFI exhibited the highest adsorption capacity for toluene (58 mg/gads) under dry gas condition while Ti-MFI had the optimal toluene adsorption performance (45 mg/gads) under the wet gas condition (the relative humidity was 50%). The simulation results indicated that the adsorption behavior of toluene on hierarchical MFI nanozeolites conformed to the Freundlich principle, and the pseudo-first-order adsorption model was suitable to elucidate the adsorption process. Moreover, the fitting result of intraparticle diffusion model indicated that the adsorption process was affected by multiple adsorption steps and the intraparticle diffusion was not the control step.

Organosilane surfactant-directed synthesis of hierarchical mordenite with enhanced catalytic performance in the alkylation of benzene with 1-dodecene

Facile synthesis of mesoporous mordenite with excellent catalytic performance for alkylation of benzene with 1-dodecene was achieved by using an organosilane surfactant as an assistant directing agent.

Catalytic upgrading of beech wood pyrolysis oil over iron- and zinc-promoted hierarchical MFI zeolites

The catalytic upgrading of beech wood pyrolysis oil has been carried out over iron- and zinc-promoted hierarchical Mordenite Framework Inverted (MFI) zeolites to produce a blendable stream with fluid catalytic cracking (FCC) feed. The iron and zinc were introduced to the zeolite structure in different loadings through the impregnation technique using metal nitrate solutions with various concentrations. The aim was to investigate the effect of zeolite acidity control along with mesoporosity of HZSM-5 zeolite on catalytic upgrading parameters. The results showed that the metal doping reduced textural properties through coverage of the catalyst surface by metal species. The existence of metals also altered acid site distribution of the hierarchical zeolite retaining crystallinity. The results of bio-oil upgrading experiments revealed a rather significant effect of extra framework metal species, particularly in 2 wt% loading, on the deoxygenation activity, coke formation potential, and selectivity towards desired products. Indeed, the improved accessibility of original and new weak and strong acid sites, as well as controlled acidity by incorporation of metals caused the enhanced conversion of large oxygenates to desired products. Zn-modified hierarchical HZSM-5 showed high selectivity towards desired oxygenates such as ketones via the promotion of carboxylic acids ketonization and reduced the formation of polycyclic aromatics. The analysis of coke also indicated that the coke yield and oxidation temperature decreased by 15% and 10%, respectively, over Zn-promoted catalyst compared with hierarchical sample showing desirable characteristics for cost-effective catalyst regeneration.

Synthesized hierarchical mordenite zeolites for the biomass conversion to levulinic acid and the mechanistic insights into humins formation

Abstract The hierarchical Mordenite zeolites are synthesized by simple seed-assisted and OSDA-free method. The crystallinity, mesoporosity and the concentration of acid sites increase significantly with hydrothermal time. Formation and growth of the zeolite crystal are observed from electron microscopy. Based on the XRD and FESEM studies, the zeolite growth mechanism is postulated to be via seed surface crystallization. With the hydrothermal time, Si(0Al) species converts to Si(1Al) and Si(2Al), as observed from 29Si and 27Al SS-NMR. The maximum levulinic acid (LA) yields of 61, 56, 52 and 43% are obtained from bamboo sawdust, cellulose, glucose and fructose, respectively, over the hierarchical H-MOR catalyst. The humins are formed from the 5-Hydroxymethylfurfural with 2,5-dioxo-6-hydroxy-hexanal as an intermediate. Even though the yield of humins is lower in the biphasic system, the yield of LA (47%) is also lowered moderately. Lastly, the reaction mechanism is postulated for the conversion of biomass to LA and humins.

Methods for reducing flue gas emissions from fluid catalytic cracking unit regenerators

The dimethyl ether (DME) carbonylation reaction over mordenite is greatly affected by the mass transfer process. In this research, hierarchical mordenite catalysts were synthesized and characterized to investigate the influence of mesopores on the structure, mass transfer and catalytic performance. The results show that the medium-strong acid sites decrease while strong acid sites increase over the hierarchical samples. The introduced mesopores can significantly improve the mass transfer efficiency and the carbonylation performances are markedly improved on the hierarchical samples. In addition, the polymerization degree of coke deposition on the deactivated samples decreases although the coke amount increases. Excessive usage of mesopore templates can damage the structure of the MOR catalysts, thus leading to the loss of acid sites and the decrease in catalytic performance.

Mordenite Nanorods Prepared by an Inexpensive Pyrrolidine‐based Mesoporogen for Alkane Hydroisomerization

AbstractWe report the synthesis of hierarchical mordenite zeolite nanorods in one step using inexpensive mono‐quaternary ammonium N‐cetyl‐N‐methylpyrrolidinium (C16NMP) as mesoporogen to the synthesis gel. The presence of a small amount of C16NMP results in the formation of 0.6–1 μm rods‐like crystals oriented along the c‐axis with a high mesoporous volume (0.12 cm3 g−1) and external surface area (∼90 m2 g−1) compared to bulk mordenite. Acidity characterization shows that the presence of C16NMP during mordenite formation leads to a redistribution of aluminum in the zeolite framework: the amount of Brønsted acid sites in the side‐pockets (8MR channels) is increased at the expense of those in the 12MR main channels. As these latter acid sites are the ones involved in the conversion of alkene intermediates in bifunctional hydroconversion of alkanes, an optimized hierarchical mordenite prepared with C16NMP displays a more ideal hydrocracking selectivity than bulk MOR prepared solely with sodium.

New method of synthesis of hierarchical mordenite of high crystallinity and its application in hydroizomerization of benzene-n-heptane mixture

A new approach to the formation of hierarchical porous structure of mordenite without use of templates is suggested in the presented work. The method is based on the crystallization of mordenite in granules consisting of amorphous aluminosilicate (metakaolin), fumed silica and mordenite crystals, provided that the crystalline phase content must be higher than that of the amorphous phase. The synthesized material is characterized by high crystallinity (up to 92%) with the volume of micro-, meso- and macro-pores of 0.15, 0.20 and 0.18 cm3/g, respectively. The research results showed that MOR type zeolite with a hierarchical structure in the H-form has total acidity in ammonia of about 860 µmol/g and after promotion of 0.3% wt platinum exhibits high activity and selectivity in the hydroisomerization of a model mixture of benzene–heptane into methylcyclopentane and isomers of n-heptane.

Synthesis and Characterization of Hierarchical Mordenite Zeolite

Synthesis and Characterization of Hierarchical Mordenite Zeolite

Hierarchical mordenite zeolite nano-rods bundles favourable to bulky molecules

Hierarchical mordenite zeolite nano-rods bundles were successfully synthesized by a novel approach of using organosilane functioned fumed silica as silicon source. The organic moiety linked on the surface of fumed silica inhibits the growth of zeolite crystal into large size, leading to the nano-rods assembled bundles. The mordenite nanorods bundles exhibited significantly improved mesitylene adsorption capacity compared with the conventional mordenite. As a catalyst, the hierarchical mordenite nanorods bundles showed remarkable catalytic performance in the benzylation of mesitylene by benzyl chloride, due to the efficient diffusion rate and improved accessibility of the active sites in the hierarchical mordenite nanorods bundles.