Mesoporous Mordenite Research Articles

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.

Preparation of mesoporous mordenite for the hydroisomerization of n-hexane

A mesoporous mordenite (MOR) zeolite was prepared from a commercially available MOR sample by a sequential acid-alkaline-acid post-treatment. The latter was used as support of Pt to prepare a bifunctional Pt/H-MOR catalyst for the hydroisomerization of n-hexane. The results showed that the available mesopores in the catalyst shorten the diffusion length of reactants and of the produced branched hexanes inside the micropores. In addition, the dispersion of supported Pt in the zeolite was increased and an enhancement in the conversion of n-hexane and at the same time the reduction of the non-selective cracking of hexane isomers and of the formation of coke (catalyst deactivation) was observed.

Hydrolysis of cellulose to glucose by supercritical water and silver mesoporous zeolite catalysts

The hydrolysis of cellulose into glucose is a critical step for the conversion of lignocellulosic biomass into fuels and chemical products. The combination of supercritical water hydrolysis in ultrafast reactors, with the subsequent hydrolysis of the cello-oligosaccharides on silver-exchanged mesoporous mordenite zeolite, offers the possibility of a clear enhancement in the conversion of cellulose and in glucose formation. Complete dissolution of cellulose is achieved in the supercritical step and 81.8% of formed oligosaccharides are hydrolyzed in the catalytic step, with a yield into glucose of 77.0%. A fraction of Al is octahedrally coordinated, indicating a distribution of acid sites after the silver exchange. A deactivation of the catalyst between the first and third reaction cycle is observed, with a reduction in hydrolyzed carbon from 81.8% up to 45.6%. However, the selectivity to glucose only varies from 94.1 to 81.8%. Afterwards, the activity remains constant up to the fifth cycle. The presence of Ag(0) particles, together with the formation of coke, are responsible for the partial blockage of the pores of the support and loss of catalytic activity.

Synthesis and Characterization of Mesoporous Mordenite Zeolite Using Soft Templates

Mesoporous mordenite zeolite samples were prepared by steam assisted conversion (SAC) method using soft templates (Brij 58, Pluronic P123, Pluronic F127 and CTABr) as drivers for mesopore generation. Samples were characterized by physical adsorption and desorption of N2, X-ray diffraction (XRD), temperature programmed desorption of ammonia (TPD/NH3) and infrared spectral analyses (FT-IR). Results indicated that samples using CTABr surfactants template showed significant mesoporosity, which was evidenced by an increase in the mesopore volume determined by the Barrett–Joyner–Halenda (BJH) method. XRD analysis and TPD/NH3 confirmed that almost all samples had mordenite structure and that total acidity was maintained. However, when a large amount of CTABr was used, a crystallinity loss was observed. Furthermore, samples were evaluated in a catalytic cracking reaction of n-heptane at 653 K and mesoporous mordenite sample showed higher catalytic activity and low deactivation rate as compared with a standard mordenite sample.

Template free facile synthesis of mesoporous mordenite for bulky molecular catalytic reactions

The synthesis of highly stable mesoporous zeolites is one of the great challenges in materials science. Soft and hard templating methods have widely been applied to synthesize mesoporous zeolites having different pore diameters and structures. Here, we report a facile and template free hydrothermal synthesis of mesoporous mordenite (MOR) by controlling synthesis conditions. The small nanoparticles of ∼50–80nm were self-assembled into 2–3μm MOR. Intracrystalline mesopores of ∼3–5nm were abundantly observed throughout the MOR nanoparticles. Synthesized mesoporous MOR demonstrated significantly improved catalytic efficiencies (∼100%), 3–5 times higher than its conventional counterparts (CBV 10A and CBV 21).

High performance of carbon dioxide adsorption of mesoporous mordenite synthesized in the presence of N,N-dimethylaniline

Mesoporous Na-mordenite zeolite was successfully synthesized by soft templating method in the presence of N,N-dimethylaniline and characterized using several techniques (XRD, SEM, BET, FTIR, and TG/dTG). The prepared material then underwent ion exchange with two alkali metal cations (K+, Cs+). Intracrystalline diffusion and alkalinity of zeolites were attributed to high adsorption capacities of CO2. Carbon dioxide capturing capacity increased in the sequence Cs-MOR > K-MOR > Na-MOR. Langmuir and Freundlich models were used to describe the adsorption behavior of CO2 over alkali-mordenite samples, and good agreement with experimental data was found.

Synthesis of large pores zeolite by soft templating strategy in the presence of novel organic template

Zeolites have a great importance in catalytic process such as isomerization and alkylation. Large pores mordenite zeolite was hydrothemally prepared by soft templating strategy using N,N-dimethylaniline as a novel structure-directing agent. The synthetized mesoporous mordenite was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N2 physical adsorption (BET), and Fourier transform infrared spectroscopy (FTIR). XRD and FTIR have been used to inform on the mordenite structure. SEM shows the crystals morphology and expanded pore opening, and N2 physical adsorption confirms the presence of mesoporous channels. The results show that in presence of N,N-dimethylaniline as organic template, mesoporous mordenite can be succefully synthesized.

Enhanced catalytic properties of mesoporous mordenite for benzylation of benzene with benzyl alcohol

Zeolite mordenite has been treated with nitric acid at different severities so as to facilitate the framework dealumination and optimization of the textural properties such as acidity and porosity. The samples obtained have been characterized by X-ray diffraction, FTIR, SEM, TEM, surface area, porosity by N2 adsorption and ammonia TPD. The resultant samples have been evaluated towards the bulky alkylation reaction of benzylation of benzene with benzyl alcohol. The studies indicated the improvement in the textural properties such as surface area, pore volume and acidity of the samples after the acid treatment. While, the phenomenon of enhancement in properties was exhibited by all the acid treated mordenite samples, the highest improvement in properties was observed at a particular condition of acid treatment (SM-2 sample). This particular sample also exhibited highest acidity and the presence of ∼10nm size pores that resulted in the effective catalytic activity towards the bulky alkylation reaction of benzene with benzyl alcohol to produce high yields of di-phenyl methane.

Mesoporous mordenites obtained by desilication: Mechanistic considerations and evaluation in catalytic oligomerization of pentene

Desilication of mordenite crystals previously enriched in silica by dealumination has been investigated in order to better understand the process of mesopore formation. Pentene oligomerization in the liquid phase in the presence of an alkane solvent has been used to evaluate the catalytic activity of the desilicated zeolite. Relevant physico-chemical characteristics such as texture, porosity, acidity and composition of zeolite samples desilicated at 80 °C in NaOH solutions at different base concentrations were analyzed quantitatively. The generation of mesoporosity is due to the hydrolysis and dissolution of the surface of the crystals, probably initiated by the formation of etch pits at low coordination atoms, followed by surface roughening, formation and growth of internal mesopores, fragmentation and, ultimately, by a complete dissolution of the crystal. Such a process which is similar to the one involved in the chemical weathering of rocks, results in a severe loss of crystalline material and of the strong acidity associated to it. The oligomerization catalyst prepared from desilicated mesoporous mordenite proved highly stable and selective for the production of C15–C30 oligomers from pentene.

Benzylation of benzene with benzyl chloride on iron-containing mesoporous mordenite

Abstract Microporous mordenite with a low Si/Al ratio was synthesized by using silicic acid powder as silica source under hydrothermal condition. By treating the mordenite with acid and base, mesoporous mordenite (M-Mor) was obtained, which was characterized by X-ray diffraction (XRD), N 2 sorption experiments, and scanning electron microscopy (SEM). Based on the M-Mor material, iron-containing mesoporous mordenite (Fe-M-Mor) was prepared by ion-exchanged method. The benzylation of benzene by benzyl chloride showed that Fe-M-Mor was a highly active catalyst in this reaction and could be reused. These results indicate that Fe-M-Mor has potential applications in Friedel–Crafts alkylations, especially of large molecules.

Synthesis of mesoporous MOR materials by varying temperature crystallizations and combining ternary organic templates

An approach, which involved perturbations of synthesis conditions in crystallization temperature and organic template composition, has been proposed for derivation of mesopores from bulk structural defects formed in mordenite (MOR) phases, based on the character of intrinsic crystal defects and tensional distortions of two compressed 8-membered rings in MOR framework. Consequently, hierarchically porous materials with MOR structures were prepared by varying temperature synthesis and using ternary organic micelles templates. The synthesized materials were characterized by powder X-ray diffraction, nitrogen adsorption at 77 K and transmission electron microscopy. These crystalline materials combined the advantages of both mordenites with the micropore system and mesoporous materials by featuring an additional intracrystalline mesopore system in MOR single crystals, resulting in a hierarchical pore distribution in range of 1.7–80.0 nm together with the significant specific surface areas. In particular, individual crystal morphologies of typical mesoporous MOR materials showed the defect-rich structures responding essentially to the mesoporosity; the mesoporous materials were substantiated matchable well to normal mordenites in acid capacity and acid strength distribution. Furthermore, several factors acting on intracrystalline mesopore formation were elucidated for explicating the perturbation synthesis approach, and whole reaction routes for synthesizing different solid products under related crystallization conditions were summarized coupling with a demonstration of part TEM micrographs. The overall results suggested that the investigative approach of perturbation imposed on crystal growth provides an alternative route for direct hydrothermal synthesis of mesoporous zeolite materials and implied that bulk structural defects within single crystals lead to the formation of intracrystalline mesopores in various sizes.

Generation of mesoporosity in MOR zeolites synthesized under perturbation conditions

The hydrothermal synthesis of various mesoporous materials with mordenite (MOR) structures is performed under perturbation conditions involving varying-temperature crystallizations and the use of ternary organic templates, and at least three types of mesoporous materials are obtained from the same starting gel containing the ternary organic templates. The greater structural diversities of these materials are found to correlate remarkably with the second-staged crystallization temperature and time. Among these materials, the two mesoporous materials crystallized incompletely over low temperature periods are differently structural composites consisting of MOR crystallites within disordered mesoporous phases, whereas the mesoporous mordenite crystallized completely over relatively high temperature period possesses the intrinsic microporosity and hierarchical mesoporosity. TEM morphological investigations on the mesoporous mordenite crystals demonstrate the formation of intracrystalline mesopores. Furthermore, an entirely new approach to synthesize mesoporous MOR zeolites is proposed based on the pore-inducing role of MOR structure defects and the adequate perturbation towards synthesis conditions.

Postsynthesis of mesoporous MOR-type titanosilicate and its unique catalytic properties in liquid-phase oxidations

Mesoporous titanosilicate with the MOR topology, denoted as Ti-Meso-MOR, was postsynthesized from commercially available mordenite by sequential acid, alkaline, acid, and TiCl 4 vapor treatments, and its catalytic oxidation properties were investigated in detail in liquid-phase oxidation reactions with hydrogen peroxide as an oxidant. A controllable acid leaching was first carried out on H-mordenite (Si/Al = 7.8) to induce a partial dealumination to Si/Al = 80, which was suitable for constructing secondary mesopores by subsequent alkaline treatment. Alkaline treatment-induced desilication introduced a large number of intracrystal mesopores. Tetracoordinated Ti species were then inserted into the resultant mesoporous mordenite with a high dealumination degree (Si/Al = 145) through the gas–solid reaction with TiCl 4 vapor at elevated temperatures. In comparison with conventional Ti-MOR and TS-1, Ti-Meso-MOR thus prepared exhibited an improved catalytic activity in the hydroxylation of toluene and the ammoximation of cyclohexanone as well. Moreover, Ti-Meso-MOR proved to be a robust catalyst for continuous ammoximation since the mesopores minimized diffusion limitation and suppressed coke formation efficiently.

Mesoporous mordenites obtained by sequential acid and alkaline treatments – Catalysts for cumene production with enhanced accessibility

Two commercially available mordenites, obtained from Zeolyst (Si/Al = 10 at/at) and BASF (Si/Al = 8 at/at), were subjected to post-synthesis treatments. The impact of acid treatment, alkaline treatment (desilication) and a combination of both on porosity, crystallinity and catalysis were studied in detail. It was found that sequential acid and alkaline treatments were most effective to obtain mesoporous mordenite with external surface areas up to 250 m 2 g −1. Electron tomography was used to visualize the mesoporosity of a series of sequential acid- and alkaline-treated mordenite samples. Mesopore formation started close to the external surface area and progressed toward the center of the crystallites for higher porosities. Liquid-phase alkylation of benzene with propylene to cumene was chosen to study the catalytic performance of the enhanced accessibility of various mordenite samples. The activity of the most porous mordenite was found to be close to that of a commercial zeolite beta, while selectivity toward the undesired n-propylbenzene was found to be significantly lower for mordenite (∼70 ppm) than for zeolite beta (∼175 ppm). These catalytic data indicate that the acid- plus alkaline-treated mordenite could be a viable catalyst in the cumene process.

Synthesis and characterization of mesoporous mordenite

Three methods were investigated to synthesize mesoporous mordenite. XRD, N 2 physisorption, SEM, and TEM showed that the mordenite obtained by acid leaching followed by base leaching of a conventional mordenite is a crystalline mesoporous material with MOR framework. The higher diffusivity of toluene indicated that mesopores benefited molecule transport through the zeolite crystal. Measurement of the number of Brønsted acid sites by n-propylamine TPD and 27Al NMR showed that the mesoporous mordenite had less extra-framework aluminum and a large number of Brønsted acid sites, while the isomerization of 2-methyl-2-pentene indicated that the mesoporous mordenite possessed a higher reactivity than conventional mordenite. The mesoporous mordenite had a much higher catalytic activity than conventional mordenite in the alkylation of benzene with benzyl alcohol. At 353 K and under atmospheric pressure, the conversion of benzyl alcohol over hierarchical mesoporous mordenite was 100% in 3 h, whereas the conversion over conventional mordenite was less than 2%. Synthesis of mesoporous mordenite with amphiphilic organosilane and carbon as secondary template did not give real mesoporous mordenite.

Alkaline-mediated mesoporous mordenite zeolites for acid-catalyzed conversions

The preparation of mesoporous mordenite zeolite and its subsequent application in the liquid-phase alkylation of benzene with ethylene is discussed. Mesoporous mordenite was obtained by controlled silicon extraction on alkaline treatment of successfully synthesized high-silica mordenite zeolites with molar Si/Al ratios in the range of 20–30. Besides substantial mesoporosity development, the combined microporous and mesoporous zeolites show preserved Brønsted acidic properties, which are highly attractive when acid-catalyzed reactions are targeted. Catalytic testing of the mesoporous mordenite found superior performance in benzene alkylation due to the unique interplay between improved physical transport in the shortened micropores and the preserved high density of acid sites.