Dealuminated H-mordenite Research Articles

Selective Isopropylation of Isobutylbenzene over H-Mordenite in Supercritical CO2 Medium: Remarkable Enhancement in Catalytic Activity and Selectivity for 4-Isobutylcumene

Remarkable enhancement in the catalytic activity and selectivity for the formation of 4-isobutylcumene (4-IBC) was observed in the isopropylation of isobutylbenzene (IBB) over highly dealuminated H-mordenite in supercritical CO2 (sc-CO2) medium. Thermogravimetric analyses confirm that reduced coking of the catalysts in sc-CO2 medium and stronger acid sites in dealuminated H-mordenite (MOR) are the key factors for superior activity and selectivity for 4-IBC.

Characterization of Gold(I) in Dealuminated H-Mordenite Zeolite

The CO interaction with Au+/dealuminated H-mordenite as well as with the nondealuminated samples, at room temperature, after evacuation at different temperatures (343, 393, 453, and 573 K) has been studied by in situ Fourier transform infrared spectroscopy. The Au+−CO band at 2192 cm-1 of the dealuminated sample showed a remarkable thermal stability on raising the temperature (till 473 K) for the degassed sample at 393 K, compared with the nondealuminated one. It has been revealed from the X-ray diffraction and X-ray photoelectron spectroscopy (XPS) analyses that the nonframework Al species were formed and embedded inside the zeolite lattice. The latter species were found to be responsible for the stability of CO coordinated Au+. The XPS data also showed the easier reduction of Aun+ species in the nondealuminated sample compared with the dealuminated one, as revealed from the peak area ratio Cl 2p/Au 4f. Adsorption of CO onto Au+/dealuminated H-mordenite, after evacuation at 343 K, produced a broad band a...

Effects of reaction temperature on the isopropylation of biphenyl over H-mordenite

The effects of reaction temperature on the selectivity for bulk products and for encapsulated products in the pores were investigated in the isopropylation of biphenyl over a highly dealuminated H-mordenite under 0.8 MPa of propylene. The selectivity for 4,4'-diisopropylbiphenyl (4,4'-DIPB) in bulk products was changed with the increase of reaction temperature: it decreased with increasing that for thermodynamically stable 3,3'- and 3,4'-DIPB. However, the selectivity for 4,4'-DIPB in encapsulated products was as high as 85–90% between 200 and 350oC. These results show that H-mordenite catalyzes the isopropylation of biphenyl inside the pore with high shape selectivity at these temperatures, and that the decrease of the selectivity for 4,4'-DIPB in the bulk products is due to its isomerization to 3,3'- and 3,4'-DIPB on external acid sites.

Kinetics of furfuryl alcohol hydroxymethylation with aqueous formaldehyde over a highly dealuminated H-mordenite

Hydroxymethylation of furfuryl alcohol with aqueous formaldehyde, yielding selectively 2,5-bis(hydroxymethyl)furan, has been carried out at 338 K in the presence of a highly dealuminated H-form mordenite. Kinetic analysis of the experimental results allows to propose an original kinetic law involving two types of catalytic sites. According to furfuryl alcohol concentration, there is competition, or not, upon these two types of sites.

A study of the non-aqueous dealumination and gallium impregnation of H-mordenite by chlorinated reagents

The in vacuo dealumination of H-mordenite by carbon tetrachloride followed by gallium impregnation using gallium(III) chloride has been studied by diffuse reflectance IR spectroscopy (DRIFTS), 71Ga, 29Si, and 27Al solid-state magic-angle spinning (MAS) NMR. Comparative studies of the interaction of carbon tetrachloride with silica and γ-alumina were also performed. IR and DRIFTS analyses of silica and γ-alumina samples show that the reaction of carbon tetrachloride at elevated temperatures can completely remove silanol and aluminol moieties at the surface of the respective oxides. The removal of intra-lattice aluminium ions is consistent with abstraction by Al3+ ion pairs. Solid state 1H NMR data, in conjunction with IR and DRIFTS analysis of the dealuminated and gallium-impregnated H-mordenite samples confirms the formation of strong Brønsted acid protons by the reaction of carbon tetrachloride. The in vacuo probe reactions of H-mordenite, dealuminated H-mordenite and gallium impregnated H-mordenite, with methanol vapour, were studied as a function of temperature. The probe reactions show that the conversion of methanol vapour with the treated H-mordenite material is a function of the reaction temperature and the chemical modification to the H-mordenite. The activity of the treated H-mordenite to produce hydrocarbons from methanol follows the series gallium impregnated H-mordenite > dealuminated H-mordenite > H-mordenite. The product distribution supports the observation that the surface adsorbed mechanisms are consistent with a series of ionogenic intermolecular reactions occurring at dual Brønsted acid–base environments within the zeolite channels. These mechanisms account for the formation of higher alcohols from methanol by the combination of carbo-ionogenic moieties and hydrocarbons produced from the dehydration of alcohols.

The effect of propylene pressure on shape-selective isopropylation of biphenyl over H-mordenite

The effect of propylene pressure on the isopropylation of biphenyl was investigated over highly dealuminated H-mordenite. The selectivity of 4,4′-diisopropylbiphenyl (4,4′-DIPB) in liquid phase products was achieved up to 90% under a high propylene pressure of 0.8 MPa, whereas the decrease of the selectivity of 4,4′-DIPB by the isomerization to 3,4′-DIPB was observed under low pressure of 0.1 MPa. However, the formation of IPBP isomers was not influenced by the pressure. The yield of 4-isopropylbiphenyl (4-IPBP) reached a maximum at 50–60% conversion of biphenyl, whereas that of 3-IPBP increased monotonously. The isomerization of 4,4′-DIPB occurred extensively under low propylene pressure, but decreased with the increase of the pressure. No significant isopropylation of 4,4′-DIPB was observed even under high pressure. The selectivities of 4,4′-DIPB encapsulated in the catalysts were more than 90% in both cases for the isopropylation of biphenyl and for the isomerization of 4,4′-DIPB under every pressure. These results of the isopropylation and the isomerization suggest that selective formation of 4,4′-DIPB occurred in the pores, and that high selectivity under high pressures is due to the prevention of the adsorption of 4,4′-DIPB at external acid sites because of preferential adsorption of propylene. The isomerization of 4,4′-DIPB under low pressures occurred on external acid sites where no propylene was adsorbed.

Cerium impregnated H-mordenite as a catalyst for shape-selective isopropylation of naphthalene. Selective deactivation of acid sites on the external surface

The impregnation of cerium is the effective method for the deactivation of external acid sites of H-mordenite. The selectivity of 2,6-DIPN in the isopropylation of naphthalene was enhanced by the impregnation with such a large amount as 30–50 wt.-% of cerium without significant decrease of catalytic activity. The highest selectivity of 2,6-DIPN was achieved up to 70% over a highly dealuminated H-mordenite, (HM(128); SiO 2/Al 2O 3= 128, with 30 wt.-% of cerium. The enhancement of the selectivity is ascribed to the deactivation of external acid sites judging from the activity of the cracking reaction of 1,3,5-triisopropylbenzene. The effective pore radius was not reduced by the modification. The ceria is highly dispersed only on the external surface of H-mordenite without any formation of new kinds of acid sites. The 129Xe NMR observation suggfests that cerium is not in the pores, but on the external surfaces. The deactivation of the external acid sites is a characteristic property for cerium. Lanthanum and neodymium inhibited catalytic activity of the isopropylation because the pores were narrowed by their impregnation. A possible reason of the deactivation is ascribed to the amphoteric property of ceria.

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.

Coke deposition, product encapsulation, and propylene oligomerization during the isopropylation of biphenyl over a highly dealuminated H-mordenite.

A highly dealuminated H-mordenite used for the isopropylation of biphenyl contained deposited coke and encapsulated products in its pores. Coke deposition occurred rapidly in the early stage, and the amount of encapsulated products was constant during the reaction. Propylene oligomerization began rapidly after the conversion of biphenyl reached 40 %, and increased up to ca. 11 % in consumed propylene. These results show that deposited coke was mainly formed from biphenyl and its alkylates, and not from propylene

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.