Dealuminated Mordenite Research Articles

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.

Selective synthesis of dimethyl ketone oxime through ammoximation over Ti-MOR catalyst

Titanosilicate with the MOR topology (Ti-MOR), postsynthesized from highly dealuminated mordenite and TiCl4 vapor through a solid–gas reaction, was highly active and selective for the liquid-phase ammoximation of dimethyl ketone (DMK) with ammonia and hydrogen peroxide. The parameters effecting the formation of the ammoximation product of dimethyl ketone oxime were investigated systematically in a batch-type reactor, and the optimized conditions were further applied to continuous ammoximation of DMK in a slurry reactor. Ti-MOR was superior to other titanosilicates in terms of activity and lifetime. TS-1 was not suitable for the ammoximation of DMK, whereas Ti-MWW required a higher catalyst loading to reach a reasonable activity, and they both easily produced a main byproduct of oxidative coupling of dimethyl ketone oxime. The deactivation behavior of Ti-MOR was investigated. Ammonia-induced structural desilication and accompanied Ti sites migration altered a more serious influence on the catalyst duration than coke deposition during continuous ammoximation.

Metal Promoted Mordenite Catalyst for Methanol Conversion Into Light Olefins

Methanol conversion was investigated on dealuminated mordenite (DM) as well as a series of promoted DM (i.e., metal/DM) catalysts prepared by impregnation. Prepared catalysts characterized by the powder XRD, BET, and NH3-TPD techniques. Chemical analysis was performed using induced coupled plasma (ICP) method. The conversion of methanol over different metal/mordenite catalysts was compared at 460°C and WHSV of 1 h−1. Several metals including Fe, La, and Ca had been used to prepare metal/DM catalysts, which displayed high selectivity toward propylene production. Ultimately, La/DM catalyst was determined to be the best material amongst those investigated for methanol conversion based upon its durability and resulting conversion.

Highly efficient synthesis of methyl ethyl ketone oxime through ammoximation over Ti-MOR catalyst

The liquid-phase ammoximation of methyl ethyl ketone(MEK) to methyl ethyl ketone oxime(MEKO) with ammonia and hydrogen peroxide was conducted over MOR-type titanosilicate(Ti-MOR),which was prepared from highly dealuminated mordenite and TiCl4 vapor by a secondary method of gas-solid phase reaction.The effects of reaction parameters on this reaction were studied systematically in a bath-type reactor.Based on the optimized reaction conditions,Ti-MOR was further employed as the catalyst for the ammoximation of MEK to MEKO in a continuous slurry reactor.This catalyst exhibited good catalytic activity and excellent MEKO selectivity in comparison to TS-1.Moreover,in terms of ketone conversion,oxime selectivity,coke resistance,and lifetime,Ti-MOR possessed the same advantages as the Ti-MWW catalyst prepared by structural rearrangement.

Clean synthesis of acetaldehyde oxime through ammoximation on titanosilicate catalysts

Acetaldehyde oxime has been synthesized though the liquid-phase ammoximation of acetaldehyde with ammonia and hydrogen peroxide over various titanosilicate catalysts. Titanium mordenite (Ti-MOR), prepared from highly dealuminated mordenite and TiCl4 vapor by a secondary synthesis method, was superior to TS-1 and Ti-MWW catalysts both in aldehyde conversion and in oxime selectivity. The reaction parameters were investigated systematically in a batch-type reactor for Ti-MOR, such as solvent effect, temperature, time, catalyst loading, amounts of ammonia and hydrogen peroxide relative to aldehyde as well as addition methods of the reactants. Under optimized conditions, Ti-MOR was capable of showing an aldehyde conversion of 99% and an oxime selectivity of 97%. In comparison with TS-1 and Ti-MWW, the advantage of Ti-MOR in acetaldehyde ammoximation was mainly attributed to its lower ability for oxidation to convert the aldehyde to acetic acid. There was almost no effect resulting from the addition mode of the reactants; Ti-MOR with its special characteristics was unique in catalytic behavior and easy handling. An overview of the reaction routes involved in acetaldehyde ammoximation has been provided.

Shape-selective alkylation of biphenyl with propylene using zeolite and amorphous silica–alumina catalysts

The influence of zeolite structure for the alkylation of biphenyl with propylene was studied over various zeolites such as HY, HZSM-5, and dealuminated mordenite (DMOR), as well as amorphous SiO2/Al2O3, in a stirred tank reactor. Biphenyl conversion was found to increase with reaction time for HZSM-5 and DMOR zeolites and reach a leveling off in 4h, whereas for HY and amorphous SiO2/Al2O3 a leveling off was reached within an hour. DMOR displayed the highest selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) even at temperatures as high as 300°C, whereas for HY, HZSM-5 and amorphous SiO2/Al2O3 selectivities fell in the range of 10–35%; they were significantly lower than observed for DMOR. These differences in selectivity might be due to the structure and pore channels of the zeolites. DMOR was found to be an active catalyst, the selectivity for 4-isopropylbiphenyl (4-IPB) and (4,4′-DIPB) was high among isopropylbiphenyl (IPB) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating DMOR possesses shape-selectivity. The selectivity of 4,4′-DIPB increased with time, while the corresponding selectivity of 4-IPB decreased for DMOR catalyst. Alkylation of biphenyl with propylene occurred with predominant formation of 4-IPB in the first step. 4-IPB is only a source in the second step of alkylation of biphenyl with propylene for the formation of 4,4′-DIPB, while 3-IPB does not participate in the formation of DIPB isomers.

An Explanation for the Enhanced Activity for Light Alkane Conversion in Mildly Steam Dealuminated Mordenite: The Dominant Role of Adsorption

This paper presents a catalytic, spectroscopic, calorimetric study of mildly steam-dealuminated mordenite (H-MOR). With increasing steam partial pressures at 673 K there is increasing dealumination, the loss of Brønsted acid sites and the presence of extra-framework Al (AlEF) likely in the zeolite pores. Additionally, the number of Lewis sites increases with increasing AlEF. As observed in previous studies, the catalytic activity for hydroisomerization of n-hexane and monomolecular cracking of n-butane and n-hexane initially increases and goes through a maximum with increasing steam severity. While the maximum increase in the rate of hexane cracking is about 5 times, the activation energies indicate that steaming does not significantly change the strength of the Brønsted acid sites. In the absence of AlEF, the enthalpy of alkane adsorption is constant at all surface coverages. However, in the presence of AlEF, the initial heat of alkane sorption increases by about 5–10 kJ/mol. After covering these adsorption sites, the heat of adsorption is identical to that on the unsteamed H-MOR until saturation coverage has been reached. The increased enthalpies of adsorption are suggested to occur on the AlEF, Lewis acid sites. Since the surface coverage of paraffins under typical reaction conditions is low, it is proposed that the enhanced rate is due to the increased initial heat of adsorption leading to a higher concentration of reactants in the steamed H-MOR zeolites.

Infrared Study of Acetophenone Adsorption on Mordenite and Dealuminated Mordenite

Infrared spectra of acetophenone adsorbed on mordenite and acid-leached mordenite are reported. The effects of dealumination were characterized by pyridine adsorption and29Si and27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). Adsorption of pyridine gave bands at 1634 and 1545 cm−1due to vibrations of pyridinium ions and a band at 1621 cm−1characteristic of pyridine ligated to Lewis acidic Al3+sites.27Al NMR gave peaks at 55 ppm due to tetrahedral framework Al and at 0 ppm due to octahedral extraframework Al.29Si NMR gave peaks at −106 and −112 ppm due to Si(1Al) and Si(OAl) species, respectively. For acetophenone on mordenite, spectra contained ν(CO) bands at 1685, 1671, 1650, and 1630 cm−1due to physisorbed acetophenone containing unperturbed CO groups, acetophenone hydrogen bonded with external and internal silanol groups, acetophenone hydrogen bonded to Brønsted acidic Si(OH)Al groups, and acetophenone ligated to Lewis acidic Al3+ions, respectively. Dealumination converted 56% of the Si(1Al) species to Si(OAl), reduced the concentrations of both framework and extraframework Al, reduced the concentration of Si(OH)Al groups, and greatly reduced the population of Lewis acidic sites, but generated internal silanol groups which formed hydrogen bonds with acetophenone molecules. Residual Al3+sites and Si(OH)Al groups after dealumination could interact with adsorbed pyridine molecules but for steric reasons were unable to form adsorption complexes with acetophenone. Evidence for the protonation of acetophenone was inconclusive.

Shape-selective ethylation of biphenyl over a highly dealuminated H-mordenite

The shape-selective ethylation of biphenyl over a highly dealuminated mordenite was examined. The ethylation, occurring stepwise, resulted in the formation of ethylbiphenyls (EBP), diethylbiphenyls (DEBP) and tri- and tetraethylbiphenyls (polyethylbiphenyls, PEBP). In the first step, the ethylation was non-shape-selective and gave 17% 4-EBP, with large amounts of the bulkier 2-EBP and 3-EBP isomers. In the second step, the pores of H-mordenite differentiated the diffusion of the EBP isomers, leading to a preferential ethylation of 4-EBP; 4-EBP was consumed rapidly. 3-EBP gradually and 2-EBP did not participate in the further ethylation. Moreover, the transition state of the ethylation of 4-EBP underwent steric restriction by H-mordenite pores, leading to an increase of the selectivity of 4,4′-DEBP up to 30%. The lack of shape selectivity in the first step and the low selectivity for 4,4′-DEBP over HM220 indicate that the space of a H-mordenite pore is too large for highly shape-selective ethylation.

Shape-selective isopropylation of biphenyl over a highly dealuminated mordenite: effect of propylene pressure

A highly dealuminated H-mordenite (H-M) catalyzed the selective isopropylation of biphenyl to 4,4′-diisopropylbiphenyl (4,4′-DIPB). The high selectivity is ascribed to the shape-selective catalysis in mordenite pores. The selectivity of 4,4′-DIPB decreased during the isopropylation of biphenyl due to isomerization of 4,4′-DIPB under low propylene pressure. The increase of propylene pressure suppressed the isomerization in the isopropylation. 4,4′-DIPB itself was isomerized over highly dealuminated H-M under low propylene pressure.

Mordenite with long life and selectivity for methanol conversion to gasoline: mordenite modified by barium ion exchange, dealumination and chemical vapor deposition of silicon methoxide

In order to develop a long-life and selective mordenite catalyst for methanol conversion to gasoline, the physico-chemical properties of mordenite were modified by three methods: dealumination, barium ion exchange and chemical vapor deposition (CVD) of silicon methoxide. Catalyst life was improved significantly by controlling acid properties both by dealumination and barium exchange. Barium ion-exchanged dealuminated mordenite with low acid site density and weak acid site strength showed the longest life amongst the catalyst so far studied by the authors. On the other hand, in order to improve the selectivity, by suppression of the formation of heavy aromatics such as pentamethylbenzene, the pore-opening sizes of dealuminated mordenite and barium ion-exchanged dealuminated mordenite were modified by CVD of silicon methoxide. In dealuminated mordenite, activity was decreased rapidly by the CVD method. In the barium ion-exchanged dealuminated mordenite, however, the formation of heavy aromatics with more than 11 carbon atoms was almost inhibited by the CVD method, while the lifetime was unchanged.

Hydrogenation of Carbon Monoxide on CO Reducing Catalyst and Solid Acid (III). The Effect of the Pore Size and Acid Properties of Zeolite on the Product Distribution

Abstract Synthesis gas reactions over hybrid catalysts composed of Pd/SiO2 and zeolites and methanol conversion on the same zeolites were studied. The selectivities to aromatic hydrocarbons were about 30% for the methanol conversions over ZSM-5, de-aluminated mordenite, and de-aluminated Y type zeolite (DAY), which possess strong acid sites. When ZSM-5 or mordenites were combined with Pd/SiO2 and subjected to synthesis gas conversion, the selectivities to aromatic hydrocarbons were between 10% and 30%. However, the synthesis gas reaction over the hybrid catalyst composed of Pd/SiO2 and DAY, gave few aromatic hydrocarbons, but aliphatic paraffins with 2 to 6 carbon atoms. Over large pore zeolites like DAY, the diffusion of olefins is so quick that most of the olefins come out of pores to be hydrogenated to paraffins on the Pd/SiO2 catalyst. In contrast, because of the slow diffusion of olefins in the medium size pores of ZSM-5 or mordenite, olefins stay in the pores for long enough to form aromatic hydrocarbons on the strong acid sites before being hydrogenated.