Tatsuaki Yashima

Selective formation of p-xylene with disproportionation of toluene over MCM-22 catalysts

Abstract Disproportionation of toluene has been studied over dealuminated MCM-22 zeolites. The dealumination of MCM-22 was performed by acid reflux and the combination of calcination or steaming with the subsequent acid reflux. These treatments effectively eliminated Al atoms from the framework site but left most of them in the crystallites as non-acidic extra-framework species. The activity of MCM-22 for the toluene disproportionation measured at relatively low temperatures (473–573xa0K) was comparable to that of mordenite and much higher than that of ZSM-5. Toluene disproportionation was found to occur mainly within the supercages of MCM-22 but not in the 10-membered ring (10-MR) channels of MCM-22 at these temperatures. The fraction of p -xylene in xylene isomers ( para -selectivity) formed on MCM-22 was higher than its equilibrium value, and increased further by the dealumination. p -Xylene formed within the supercages as a primary product would be isomerized to o - and m -xylene by the acid sites not only on the external surface but also within the 10-MR channels. The improvement in para -selectivity by the dealumination resulted from the suppression of isomerization activity probably because the dealumination treatments eliminated framework Al atoms predominantly on the external surface and inside the 10-MR channels compared with those inside the supercages.

Isomerization of n-heptane over Pt-loaded zeolite β catalysts

Abstract The influence of key parameters in the isomerization of n -heptane over Pt-loaded Hβ catalysts was studied at temperatures lower than 250°C under atmospheric pressure. The highest yield of isomerized products was obtained at 210°C. The conversion of n -heptane increased with contact time (W/F), while the selectivity to isomers decreased. The higher the hydrogen partial pressure, the higher the selectivity to isomers. It was found thatPt/Hβ catalyst showed a good stability for 78 h at the reaction temperature of 220°C. The effect of metallic sites and acid sites (Si/Al ratios) on the catalytic property was studied. The higher the content of Pt, the higher the selectivity to isomers, and the lower the acidity of zeolite β, the higher the selectivity to isomers at the same conversion.

Isomerization of n-hexane over Platinum loaded zeolite catalysts

Abstract The isomerization of n-hexane over Pt-loaded Hβ, H-ZSM-5 and H-dealuminated mordenite was studied at temperatures lower than 573 K under atmospheric pressure. It was found that Pt loaded H β showed the highest activity and selectivity of these three catalysts. Namely, the conversion of hexane was 76 C-% and selectivities to dimethylbutanes, methylpentanes and cracking products were 19.4, 76.2 and 4.4 C-%, respectively, under the following conditions: reaction temperature, 548 K; W/ F, 5 g h mol −1 ; molar ratio of hydrogen to n-hexane, 4. Pt/Hβ catalyst showed a good stability, because Hβ has acid sites with medium strength and three-dimensional large pores. We can adjust the balance between metallic sites and acid sites to obtain right catalyst which has the highest activity and the highest selectivity for the isomerization of hexane.

Vapor phase Beckmann rearrangement of cyclohexanone oxime on the zeolite catalysts

Abstract Effective zeolite catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime have the smaller pore window size than cyclohexanone oxime and have very weak acid sites. Ethanol is useful solvent for cyclohexanone oxime to improve the selectivity for ϵ-caprolactam formation.

Acidic and catalytic properties of aluminated mordenite zeolite: effect of extraframework aluminium

The nature of the extraframework aluminium generated in dealuminated mordenite by alumination with AlCl3 and its effect on acidity and catalytic activity have been studied. A series of mordenites with framework Si/Al atomic ratios between 11 and 220 was obtained by alumination of dealuminated mordenite and was characterized using atomic absorption spectrophotometry, IR spectroscopy, MAS NMR and reaction studies.Alumination below 873 K preferentially introduced Al atoms into the extraframework sites instead of into the framework sites, while alumination at 873 K and higher temperatures led to the incorporation of more Al into the framework. In all cases a significant portion of the extraframework Al species was not ion-exchangeable with an aqueous solution of NH4NO3 and was unobservable by 27Al MAS NMR, suggesting its lack of symmetry. IR studies with NH3 and pyridine probes demonstrated that the extraframework Al species acted as Lewis acid sites. The mordenite aluminated at 873 K showed a comparable specific activity to the parent and dealuminated mordenite for toluene disproportionation and o-xylene coversion as measured by turn-over frequency based on the number of Bronsted acid sites. Those aluminated below 873 K, however, exhibited enhanced specific activity for both reactions. The enhancement is explained by the Lewis acidic extraframework Al exhibiting electron-withdrawing properties and thus intensifying the Bronsted acidity of the framework Al.

Synthesis of 3-methyl-3-butene-1-ol from isobutene and formaldehyde on FeMCM-22 zeolites

Abstract The synthesis of 3-methyl-3-butene-1-ol(MBOH) from isobutene and formaldehyde in the liquid phase over various kinds of zeolites was studied. It was found that for the selective formation of MBOH the suitable pore window size and strength of acid sites were requested. Namely, the pore structure of MCM-22 was suitable size to depress shape-selectively the formation of 3-methylbutane-1,3-diol and 4,4-dimethyl-1,3-dioxane which were main by- products, and the medium strength of acid sites of H-FeMCM-22 was effective to lengthen the catalyst life. Under the optimum conditions, 45% of the conversion of formaldehyde and 90 mol% of the selectivity for MBOH formation could be obtained over H-FeMCM-22 whose external surface was poisoned by 4,4-dimethylquinoline.

Transformation of n-butane over HZSM-5 and other MFI type zeolites

Transformation of n-butane was studied over HZSM-5, silicalite, ferrisilicate and modified HZSM-5 zeolites. It was found that silicalite gives the lowest conversion and no aromatic selectivity. Modification with gallium has increased conversion as well as aromatic selectivity. HZSM-5 gave the highest conversion and Ga-HZSM-5 (ion exchange) the highest aromatic selectivity. In case of ferrisilicate, conversion was better than silicalite and aromatic selectivity was better even than that of HZSM-5. Both conversion and aromatic selectivity increased profoundly when ferrisilicate was impregnated with gallium. Gallium is thought to enhance both conversion and aromatization.

Modification of mordenite acidity by isomorphous substitution of trivalent cations in the framework sites using the atom-planting method

Abstract Aluminum, gallium and antimony cations were incorporated into the framework of highly siliceous mordenite to modify the acid strength of Bronsted acid sites by the ‘atom-planting method’ with the corresponding metal chloride vapors at elevated temperatures. The framework incorporation of metal cations was confirmed by IR, MAS NMR and catalytic reactions. The optimum temperature to achieve a maximum incorporation of metal cations into the mordenite framework was demonstrated to be 873 K. Tetrahedral Ga cations exhibited an IR band owing to acidic bridging Si(OH)Ga groups at 3620cm−1 and a characteristic band at 159 ppm in the 71Ga MAS NMR spectrum. The IR band owing to bridging Si(OH)Sb groups was observed at 3663 cm−1. The acid strength of Si(OH)Me (Me = Al, Ga and Sb) groups estimated from their IR frequency, IR spectra of adsorbed pyridine and the activity for toluene disproportionation and cumene alkylation with 2-propanol was in the order Si(OH)Al>Si(OH)Ga> > Si(OH)Sb. The weakest acid sites, Si(OH)Sb, inactive for the toluene disproportionation, showed a significant activity for the cumene alkylation with higher para-selectivity.

Synthesis of ferrisilicate with the MCM-22 structure

A new ferrisilicate molecular sieve with the MCM-22 structure is nsynthesized in Al-free form and exhibits low activity as a solid-acid ncatalyst and significant activity for the selective catalytic reduction of nNO with NH n 3 n.