Cobalt‐loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared‐mass spectroscopy temperature‐programmed desorption, transmission electron microscopy, X‐ray absorption near edge spectroscopy and extended X‐ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono‐atomically dispersed on the ion exchange site of MFI zeolite was the active species.

Tottori University research result repository タイトル Title Shape selectivity in toluene disproportionation into para-xylene generated by chemical vapor deposition of tetramethoxysilane on MFI zeolite catalyst

Dealkylation of alkylnaphthalene, as a model of alkyl polycyclic aromatic hydrocarbon compounds in heavy oils, proceeded selectively on a silica monolayer solid acid catalyst. The activity was generated by the deposition of silica on alumina with generation of Brønsted acidity. The activity and Brønsted acid amount showed the maximum where the monolayer covered the surface, indicating that the Brønsted acid site generated on the silica monolayer was the active species. The activity and selectivity on the silica monolayer were high compared to other aluminosilicate catalysts, and high activity was observed even after calcination at 973-1173 K.

Impregnation of various heteroelements on the ZSM-5 zeolite was applied to improvement of the catalytic activity in toluene disproportionation. Nickel loaded on ZSM-5 (Ni/ZSM-5) exhibited higher catalytic activity (toluene conversion) and lower benzene / xylene ratio (closer to the stoichiometry, meaning low rate of side reaction) than H-ZSM-5 zeolite. The Ni/ZSM-5 with Ni/Al = 0.6 showed the maximum in catalytic activity, and excess Ni loading caused decrease in the conversion and increase in the benzene / xylene ratio due to decrease of acid amount and acceleration of dealkylation, respectively. The detailed analysis of acidic property by means of 2 ammonia IRMS-TPD method showed that the Ni loading generated Lewis acid sites on the zeolite. The synergy of Brønsted and Lewis acid sites, ascribed to Si-OH-Al and Ni species, respectively, is suggested to give the high activity of desired reaction.

Reaction rates of toluene disproportionation (A) and cumene cracking (B) normalized by the number of Brønsted acid sites were analyzed on aluminosilicates. The activation entropy showed linear and compensatory relationship against the activation enthalpy. The slope of entropy-enthalpy plot was in the order of (B) > (A) > small alkane cracking, whereas the intercept on the horizontal axis was in the order of propane and isobutane cracking > linear C4-8 alkanes and iso-pentane cracking > (A) > (B). The former is consistent with the bulkiness of reactant, while the latter is consistent with intrinsic difficulty of formation of intermediate cations.