Facile preparation of nanocrystal-assembled hierarchical mordenite zeolites with remarkable catalytic performance

The present study reports a novel strategy to fabricate nanocrystal-assembled hierarchical MOR zeolites. This is the first demonstration of hierarchical MOR without preferential growth along the c-axis, which facilitates mass transfer in the 12-membered ring channels of MOR zeolite for the conversions involving bulky molecules. The facile method involves the combined use of tetraethylammonium hydroxide （TEAOH） and commercial surfactants, in which TEAOH is essential for the construction of nanocrystal assemblies. The surfactant serves as a crystal growth-inhibiting agent to further inhibit nanocrystalline particle growth, resulting in enhanced mesoporosity. The hierarchical MOR assembled particles, constructed of 20-50-nm crystallites, exhibit superior catalytic properties in the alkylation of benzene with benzyl alcohol compared with the control sample, as the hierarchical MOR possesses a larger external surface area and longer c-axis dimension. More importantly, the material shows improved activity and stability in the dimethyl ether carbonylation to methyl acetate reaction, which is a novel route to produce ethanol from syngas.

Activity and basic properties of KOH/mordenite for transesterification of palm oil

The catalytic performance of KOH/mordenite has been studied for transesterification of palm oil using a batch reactor and a packed-bed reactor at 60 C and atmospheric pressure.The KOH/mordenite processed transesterification in the batch reactor gave the highest methyl ester yield of96.7%under optimum conditions,while a methyl ester content over 94.5%was obtained in the packed-bed reactor.This comparison indicates that transesterification in a batch-type reactor gives a higher methyl ester yield than that of a continuous-flow reactor.Dealumination was found in the calcined catalysts and had a significant effect on the physical structure and chemical composition of the catalysts.Leaching of the potassium species was negligible,whereas depositing and washing of the reacted mixture with acetone on the catalyst surface were observed by FTIR.

Distribution of Fe and adsorption of NH_3 in mordenite:a computational study

The distribution of Fe and the adsorption of NH3 in H-[Fe]MOR （mordenite） were investigated using dispersion corrected density functional theory （DFT-D2）.Based on the results,it can be found that the most favorable site for the distribution of Fe is T1O6,followed by T2O5,T4O2 and T3O1,and energy differences for Fe in different T sites are less than 0.09 eV,indicating that Fe atoms may distribute in all kinds of T sites in MOR.In addition,the adsorption energies for NH3 at each crystallographic position of H-[Fe]MOR were also determined.Finally,it can be concluded that the Br（o）nsted acid site at T2O5 is stronger than the other acid sites,and the adsorption of NH3 on Br（o）nsted acid sites is more stable than on Lewis acid sites.

Selective conversion of methanol to propylene over highly dealuminated mordenite:Al location and crystal morphology effects

The growing consumption of light olefins has stimulated intensive researches on methanol to olefin(MTO)process which possesses great advantages for coal conversion to value‐added chemicals in an environmentally benign way.The catalysts commonly used for MTO process faces several challenges such as poor selectivity control,low hydrothermal stability and short lifetime.In the present study,we prepared a series of mordenite zeolites with variable Al contents(Si/Al molar ratios of 51−436)by a sequential dealumination treatment of air‐calcination and acid leaching.The textural properties,acidity and Al location before and after the dealumination treatment have been systematically studied and their effect on MTO especially the methanol to propylene(MTP)performance was thoroughly investigated.The mordenite zeolites with the Si/Al ratios over 150 selectively catalyzed methanol conversion in the MTP pathway,providing a high propylene selectivity of 63%and propylene/ethylene ratio of>10.Compared to the low‐silica MOR catalysts,highly dealuminated MOR showed much higher stability and longer lifetime,which can be further enhanced via harsh hydrothermal pretreatment.Furthermore,the lifetime was highly related to the crystal size along c‐axis.The excellent performance of highly dealuminated MOR is likely ascribed to the mesopores formed upon dealumination and the scarce Al sites located in the T sites shared by the 8‐member ring(MR)side pockets and 12‐MR pore channels.

Preparation, Characterization and Optical Properties of Host-guest Nanocomposite Material Mordenite-silver Iodide

Silver iodide nanoclusters were successfully prepared in the channels of mordenite by a heat diffusion method. Powder X ray diffraction, adsorption technique and infrared spectroscopy were used to characterize the prepared materials, which showed that the guest silver iodide had been encapsulated in the channels of mordenite. The optical properties of the solid phase diffuse reflectance absorption of nanocomposite material NaM AgI were studied, showing that the absorption bands of the diffuse reflectance absorption of the prepared material moved to the region of high energy. The absorption peak of the material prepared shifted to the region of high energy. Namely, blue shift was caused. This has demonstrated the incorporation of silver iodide into the channels of the zeolite. We observed the luminescence and surface photovoltage spectra of NaM AgI sample, proposing the mechanisms of the photoluminescence and photovoltaic responses.

Highly selective methanol-to-olefin reaction on pyridine modified H-mordenite

The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity（> 65.3%） of C;-C;, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30 min to more than 120 min after the modification with pyridine.1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts’ lifetime. It can be concluded from ex-situ;C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.

Syntheses of Ferrierite and Mordenite Zeolites from Dried Gel in Alcoholic System

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N-Hexane Isomerization on Ni-Pt/Catalysts Supported on Mordenite

The aim of this work was to evaluate the catalytic properties for n-hexane isomerization of bifunctional monometallic (Ni or Pt) and bimetallic catalysts (Pt-Ni), using HMOR zeolite as support. The method used for metal dispersion in the zeolite was competitive ion exchange using ammine complexes [Ni(NH3)6]Cl2 and [Pt(NH3)4]Cl2 as precursors. The catalysts were characterized by X-Ray diffraction, X-Ray energy dispersion spectroscopy, temperature-programmed reduction and transmission electron microscopy. The n-hexane isomerization reaction using the catalysts was carried out to evaluate the catalyst activity. The reaction was carried out in a fixed bed reactor operating at 250?C, 1 atm, H2/C6 = 9 molar ratio. The profiles obtained from TPR suggest that, for bimetallic catalysts, the presence of platinum facilitates the reduction of Ni2+ cations. The bimetallic catalysts presented a higher activity in the isomerization of n-hexane when compared to the monometallic ones, as well better stability as the Pt content in the solid increases.

Influence of γ-Alumina Binder on Acidic Properties of Mordenite Catalysts

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Growth mechanism of a preferentially oriented mordenite membrane

A preferentially oriented mordenite membrane was successfully prepared on a seeded porous α-alumina support. Characterization results of XRD (X-ray diffractometer) and FE-SEM (field emission scanning electron microscope) revealed that evolutionary selection might predominantly contribute to the formation of the sharply oriented mordenite membrane. The nec- essary conditions under which evolutionary selection occurs are: (a) the number density of nuclei on the support surface should be high enough at the early stage; (b) the crystals should grow fastest along one direction; and (c) the zeolite layer should proceed via the successive growth of the crystals nucleated on the support surface instead of the accumulation of the crystals formed in the bulk solution.

Study on RE-Modiffied Mordenite Catalysts for Amination Reaction

The effects of RE modified mordenite catalysts on the activity and selectivity of amination reaction at atmospheric pressure in a fixed bed reactor were studied. The experimental result shows that the Y modified mordenite catalyst exhibits very good activity and selectivity to dimethylamine(DMA). The results of the catalyst characterization demonstrate that the rare earth modification of mordenite mainly causes the changes of B acidic sites in mordenite. The crystal structure and the Si/Al ratio on the surface of mordenite basically remain unchanged after mordenite is modified by rare earth elements. Rare earth modification improves the thermal stability and prolongs the life of the catalyst.

Natural Mordenite Catalyst Used on the Ammoniation of Methanol

The catalytic properties of natural mordenite as acidic catalysts were investigated using the ammoniation of methanol.

Alkylation of o-Xylene with Styrene over Modified Mordenite for Environmentally Friendly Synthesis of PXE

Effects of hydrochloride acid dealumination of mordenite(MOR) catalysts for the synthesis of 1-phenyl-1-xylyl ethane(PXE) were investigated. The structure and acidity of catalysts were characterized by XRD, BET, XRF, FT-IR, 27Al NMR and NH3-TPD techniques. The catalytic performance of the acid-treated MOR zeolites was studied through using the alkylation of o-xylene with styrene. The test results showed that the strength of remaining Br?nsted acid sites increased despite the reduction of total number of acid sites after dealumination, and the micropores of HMOR were slightly enlarged coupled with the formation of secondary mesopores. Additionally, the modified HMOR zeolites showed longer catalyst life with the styrene conversion rate retained. Among the catalysts employed in this study, the modified mordenite that was dealuminated by HCl(2 mol/L) could be used repeatedly without significant loss of activity and selectivity during six catalytic runs, which have been ascribed to its specific acidity and structural properties.

A Novel Friedel-Crafts Acylation Reaction of Anisole for Production of 4-Methoxyacetophenone with High Selectivity and Sufficient Reusability of Mordenite Zeolite Catalyst

Zeolite catalyzed Friedel-Crafts reactions were examined using acetic anhydride as an acetylating agent and an acetic acid as a solvent. It revealed that the reaction of anisole smoothly occurred quantitatively for 3 h using mordenite zeolite with SiO2/Al2O3 = 200, and with SiO2/Al2O3 = 110, the increasing of Br?nsted acidity allowed to completely react within 2 h. Furthermore the selectivity of 4-methoxyacetophenone (4-MA) among the isomers was found to be quantitative, no by-products and/or isomers were not detectable. With the excellent recyclability and reusability, the mordenite zeolite exhibited at least 30 times quantitatively both conversion of anisole and selectivity of 4-MA. The mordenite catalysts of fresh and the used after 30 times were characterized. This opportunity obviously indicates the sufficient shape selective catalyst of mordenite zeolite and gives a green synthetic tool for heterogeneous acylation reaction.

Isolated zinc in mordenite stabilizing carbonylation of dimethyl ether to methyl acetate

Herein, we prepared a series of H-Zn-mordenite (H-Zn-MOR) catalysts by adding zinc source into the initial sols during the synthesis of mordenite (MOR). The results indicated that isolated Zn ions were highly dispersed in the catalysts. The addition of zinc led to the increase of Si/Al in the framework of MOR,the change of the distribution of acid sites and the change of acid strength. We investigated the catalytic performance of the H-Zn-MOR catalysts and the HMOR catalysts for carbonylation of dimethyl ether to methyl acetate. The addition of zinc improved the catalytic performance and made the drop of the conversion over the Zn-0.003 and Zn-0.005 catalysts to be about the half of that over the HMOR catalyst.We attributed it to the change of the acid properties, which further change the rate of coke deposition.

Direct conversion of methane to methanol over Cu exchanged mordenite:Effect of counter ions

Direct conversion of methane(CH4)to methanol(DMTM)is a promising,but very challenging process for the utilization of abundant CH4 as a low carbon resource.In this context,Cu loaded zeolites,mordenite(MOR)in particular,were recognized as the most effective system to perform DMTM.In this work,different Cu salts were used to exchange with MOR,by which the effect of counter ions on the catalytic performance towards DMTM was investigated.The prepared catalysts were characterized and evaluated systematically.It was found that the counter ions affected the speciation of Cu sites,probably due to their capability in extraction of protons from MOR and the influence on the hydrolysis state of the Cu2+in aqueous solution.These behaviors adjusted the association between Cu2+and the exchangeable protons in MOR.As a result,varied DMTM performance was observed.Among the used Cu salts,Cu(CH3COO)2 exchanged MOR showed the highest performance,achieving stable CH3 OH yield of 117±28μmol/g in 5 consecutive cycles,these values are among the highest for Cu loaded MOR zeolites in open publications.

Superior Storage Performance for NO in Modified Natural Mordenite

Natural mordenite （NMOR）, modified by acid treatment and ion-exchange, was employed for NO adsorption in the present study. The NO storage capacity of modified NMOR was greatly improved compared with its original correspondents, mainly due to the preservation of crystalline structure and the improvement of surface area of NMOR. Among all the modified NMOR, Ni-NMOR exhibited the highest adsorption capacity for NO （1.20 mmol-g^ 1） in the presence of 10% 02 at 308 K. The influence of the main ingredients in flue gas on the storage capacity of NMOR for NO had also been investigated. In general, H2O, CO2 and SO2 all displayed negative impact on NO adsorption due to their competitive adsorption on the surface of NMOR with NO, while the presence of 02 greatly improved the adsorption of NO because of the formation of NO2 and N203. Moreover, Ni-NMOR exhibited high efficiency for NOx removal through the NOx adsorption-plasma discharge process.

Synthesis of ultra-small mordenite zeolite nanoparticles

The mordenite（MOR） nanoparticles（MNPs）with ultra-small crystallites（~30 nm） were synthesized by using tetraethylammonium bromide（TEAB） as structure directing agent at low temperature（403K）. The formation of MNPs was considered to be due to high concentration of TEAB and occurrence of limiting Ostwald ripening at low temperature. The MNPs exhibited not only higher catalytic activity at low temperature for selective catalytic reduction of NOx but also higher catalytic activity and longer lifetime for disproportionation of toluene than conventional MOR（cMOR） bulk crystals.

NMR invisible" aluminum species in dealuminated mordenite zeolite:a ~1H/^(27)Al TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced 1 H/ 27 Al TRAPDOR method as well as 27 Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0±0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non framework aluminum species Al(OH) n , respectively. The source of the "invisible Al" is discussed on the basis of the NMR experimental results.

Synthesis and ion exchange properties for Cs^+ of ammonium-type mordenite

Cesium content in the seawater is 3.0 9 10-4 mg·L-1, and ammonium-type mordenite was used to exchange cesium from cesium source. K-type mordenite was obtained by hydrothermal synthesis method. After ammonium-modified, ion exchange properties such as saturated ion exchange capacities and selectivity coefficients for alkali metal ions were determined. At the same time, ion exchange isothermal curves of ammonium-type mordenite for Cs+ and NH4+ were determined at 25°C.Pitzer electrolyte solution theory was used to work out activity coefficients of the system, and the Kielland diagram of the ion exchange system was obtained. The calculated equilibrium constant(Ka) and ion free enthalpy(DG0) of mordenite for Cs+ and NH4+ are 1.455 and -930.3J·mol-1, respectively, indicating that ion exchange process of ammonium-type mordenite for cesium is a spontaneous process.