Forms Of Mordenite Research Articles

Catalytic dehydromethylation of methylcyclohexane and the simultaneous transformation of fractions of straight-run gasoline and methanol with modified forms of mordenite and pentasil

Results are presented from studies of the dehydromethylation (DHM) of methylcyclohexane (MCH) and the simultaneous transformation of straight-run gasoline fractions and methanol on modified forms of mordenite and pentasil in the presence of various hydrogen acceptors (O2, CO2). High selectivity on xylene isomers is observed for polycationic modifications of HNa-TsVM. On such catalytic systems, the degrees of DHM and dehydrodisproportionation (DHD) of MCH grow with an increase in O2-to-CO2 ratio in the range of 0.05 : (1–1.5), while the degree of its dehydrogenation to toluene is virtually constant. High yields of di- and trimethylbenzenes are achieved in the reactions between methanol and gasoline fractions composed mainly of C7–C8 hydrocarbons at 100–140 °C. The results from this study can be used for straight-run gasoline reforming with the aim of increasing the yield of C8-C9 aromatic hydrocarbons.

Gas-phase and supercritical n-pentane isomerization on H-mordenite

The skeletal isomerization of supercritical n-pentane on the H form of mordenite under flow conditions was studied for the first time. It was found that the conversion of supercritical n-pentane was 30–35% at 90% selectivity for isopentane at 260°C, 130 atm, and a liquid hourly space velocity of 30 h−1. The catalyst was deactivated as the temperature was increased above 280°C. According to differential thermal analysis data, the deactivation was related to the deposition of condensation products on the surface. The resistance of the H form of the zeolite to poisoning in n-pentane isomerization in a gas phase at 1–8 atm was lower than that under supercritical conditions. It was found that H-mordenite deactivated under gas-phase reaction conditions at 260°C and 8 atm can be regenerated by passing to supercritical isomerization conditions (260°C and 130 atm).

IR Spectroscopic Study of Ethylene Adsorption and Oligomerization on the Hydrogen Form of Mordenite

Diffuse-reflectance IR spectroscopy is used to study adsorption and oligomerization of ethylene on the hydrogen form of mordenite at room temperature. Ethylene adsorbs on bridging acid hydroxyl groups of the zeolite and forms π-complexes with a firm hydrogen bond. The interaction with hydroxyl groups most strongly excites composite vibrations in adsorbed molecules. These vibrations are a combination of the stretching vibration of a double bond and the deformational vibrations of the CH2 group. A conjecture is drawn that these composite vibrations correspond to the reaction coordinate of ethylene transformation to the ethoxy groups. Their further reactions with weakly adsorbed molecules result in ethylene oligomerization. A linear oligomer is formed, grafted on the zeolite surface and filling the pores of zeolites.

Preparation and Characterization of a Composite of Silver Iodide and Synthetic Mordenite

A composite material made up of AgI and the potassium form of mordenite has been prepared by treating the silver form of synthetic mordenite with potassium iodide. The composite as well as the silver and potassium forms of mordenite have been characterised by X-ray powder diffractometry, X-ray photoelectron spectroscopy, EDS analyses and ac conductivity measurements. It has been inferred that, in the composite material, AgI grows at the entrance of the zeolite channels without forming a continuous conducting phase. The silver form of mordenite has been proved to be a silver ion conductor by dc conductivity measurements.

Influence of Brnsted acidity on the redox properties of silver species in zeolite mordenite

The redox behaviour of Ag+ ions exchanged into zeolites is strongly influenced by the presence and concentration of Bronsted acid sites (BS). This is demonstrated by a temperature programmed reduction study of various samples prepared by ion exchange into the Na+ form or by impregnation of the H+ form of mordenite with AgNO3 solution. The Bronsted acidity of the latter was varied by different ways of transforming the NH4+ form to the H+ form. High concentration of BS as well as a high Ag loading favours the reoxidation of A formed in the reduction process. On acidic, Ag-loaded mordenites, a complete reduction of Ag+ occurs only at relatively high temperatures (above 600°C) where the BS are progressively destroyed.

Electron spin-echo and electron spin-resonance studies of cupric ion-adsorbate interactions in H-, Na-, K-, and Ca-mordenite

The interaction between cupric ion and both polar and nonpolar adsorbates in mordenite-type zeolite was studied as a function of the cocation. Cu{sup 2+} was able to coordinate to three molecules of either water or ammonia in H-mordenite but to only two molecules of each in Na-, K-, or Ca-mordenite. These results suggest that Cu{sup 2+} is located in a site off the main channel in H-mordenite but in a highly twisted 8-ring site in the other forms of mordenite. Evidence based on adsorption and activation studies also suggests that some Cu{sup 2+} is located in an additional, unidentified site in H-mordenite. These results are compared to the results of similar studies of cupric ion in zeolite ZSM-5.

THE ELECTRICAL CONDUCTIVITY OF MORDENITE

The electrical conductivity and electron electrical conductivity of mordenite has been measured. The electrical conductivity and the activation energy of mordenite containing different water and ion-exchanged forms of mordenite have also been measured. The results show an ionic conductivity: the specific conductivity of mm denite is 10-6 to 10-5(Ω·cm)-1 in natural environment. The electrical conductivity of mordenite shows the change of its structure.

Fine control of the pore-opening size of the zeolite mordenite by chemical vapour deposition of silicon alkoxide

Chemical vapour deposition (c.v.d.) of Si(OCH3)4 on the H form of mordenite has been carried out in order to control the pore-opening size without affecting its acidic properties. It has been shown that Si(OCH3)4 is deposited irreversibly on the zeolite. Because the molecular size of the alkoxide is larger than the pore size, the alkoxide does not enter the pore and the silicon compound is deposited on the external surface. The alkoxide may be deposited by reaction with hydroxide, thus covering the external surface of zeolite crystal after subsequent reactions. Calcination with oxygen removes the hydrocarbon residue and produces silica-coated H-mordenite (SiHM). The SiHM thus obtained has been characterized by temperature-programmed desorption (t.p.d.) of NH3, adsorption experiments and X-ray photoelectron spectroscopy. The deposition of the alkoxide does not change the acidity but reduces the size of pore opening. Enrichment of Si on the external surface of the zeolite is confirmed. One can therefore conclude that SiO2 covers the external surface of the zeolite, thus reducing the effective size of the pore opening. The pore size is effectively reduced by ca. 0.1 and 0.2 nm upon formation of 1–2 and 3 molecular layers of silicon oxide, respectively.

X-ray diffraction criteria for evaluation of the concentration and state of aluminum in mordenites

1. The x-ray diffraction patterns of dealuminized mordenites in the range of small and intermediate angles contain reflections whose intensities correlate with the change of the aluminum content in the framework. 2. During heat treatment of the ammonium form of mordenite at 500–650°C, up to 50% of the aluminum atoms can be removed from the framework.

Study of the adsorption properties of a natural Hungarian mordenite and its ion-exchanged derivatives

The texture and adsorption properties of a natural, Hungarian mordenite were investigated by electron microscopy and BET adsorption measurements. The properties of the ion-exchanged adsorbents were characterized by CO2 and SO2 isotherms. The measurements were evaluated on the basis of the pore-filling theory of Dubinin. We have found that at 20°C the H+-form of mordenite interacts preferably with CO2, while on the Na+- and Ca2+-derivatives stronger adsorption of SO2 takes place. This fact accounts for their applicability as selective adsorbents.

Investigation of the catalytic conversions of acetone on cationic forms of faujasite and mordenite

1. At 200–450° and a pressure of 30 atm, type-Y zeolites, containing cations of metals of groups I, II, and the rare earth elements are active in the hydrogenation of acetone. A correlation of the activity of the catalysts with the value of the electrostatic potential of the anions (e/r2) was noted. 2. The activity of samples of NaHY and NaHM, produced by decationization of Na forms of zeolites and recationization of NH4Y and NH4M, increases with increasing concentration of Na+ cations, which indicates the participation of these cations in hydrogenation reactions. 3. The catalytic properties of decationized and recationized forms of mordenite of the same composition do not differ. NaHY zerolites, produced by recationization of NH4Y, are more active than HNaY prepared by decationization of NaY, which is evidently due to the different arrangement of the Na+ ions in the structure of the indicated catalysts.

Formation and properties of the hydrogen form of mordenite Communication 9. Thermal stability of certain cationic forms of synthetic mordenite

1. The degree of exchange of Na+ of synthetic mordenite for other cations decreases with increasing polarizing ability of the cation. 2. The acid resistance of cationic forms of mordenite increases with increasing polarizing ability of the exchange cation. 3. Thermal decomposition of the ammonium form of mordenite in air leads to the formation of the hydrogen form of mordenite, possessing lower acid resistance than HM produced by the action of acids on the Na-form.

Chemical modification as a method of controlling the adsorption properties of the sodium form of mordenite

1. The process for the recationization of a slightly dealuminized mordenite leads to obtaining a sample, the adsorption properties of which are close to the properties of the “wide-pored,” mordenite described in the literature. 2. The recationized mordenite differs from the Na form of the “narrow-pored” mordenite by a different arrangement of the cations.

Investigation of the kinetics of the isomerization of n-pentane on the hydrogen form of mordenite at low partial pressures of hydrogen

1. The kinetics of the isomerization of n-pentane on the H-form of mordenite was investigated at partial pressures of hydrogen of 2–6 atm. 2. The degree of deactivation of the catalyst and the corrected reaction rate under these conditions were determined. 3. The heat and entropy of the formation of the n-amyl cation were determined, and an independent approximate calculation of these parameters was performed.

Formation and properties of the hydrogen form of mordenite

Formation and properties of the hydrogen form of mordenite

Formation and properties of the hydrogen form of mordenite

1. The adsorption of vapors of n-pentane and diethyl ether by sodium and modified hydrogen forms of mordenite experiences a strong kinetic inhibition, which makes it difficult to obtain reversible isotherms of equilibrium adsorption. 2. Despite the low rate of adsorption and difficulty of achieving adsorption equilibrium, the bulk of the adsorbed substance is adsorbed at very low relative pressures. 3. An increase in the degree of dealumination, leading to an enlargement of the micropores, promotes an increase in the magnitude and rate of adsorption of n-pentane and diethyl ether vapors. 4. The adsorbability of diethyl ether vapors on samples of H-mordenite with a high degree of dealumination is 30–40% higher than that of n-pentane vapors.

Method for increasing the adsorption capacity of the sodium form of mordenite

Method for increasing the adsorption capacity of the sodium form of mordenite

Formation and properties of the hydrogen form of mordenite

Formation and properties of the hydrogen form of mordenite

Formation and properties of the hydrogen form of mordenite

Formation and properties of the hydrogen form of mordenite