Environments of Ga in MFI-Type Ga-Silicates and Their Catalytic Performances

Abstract

MFI-Type Ga-silicates with various Si/Ga ratios were synthesized from gels prepared using two different preparation methods: an alkoxide method ((A)) and a Mobil method ((M)). Gallium-silicates(A) from an alkoxide method were compared with Ga-silicates(M) from a Mobil method in terms of their physical properties and catalytic performances in C₄H₁₀ conversion-reaction. The line width of a peak assigned to tetrahedral GaO₄ in the ⁷¹Ga-MASNMR spectrum of Ga-silicate(M) was broader than that of Ga-silicate(A), and the unit cell volume of Ga-silicates(M) was less than that of Ga-silicates(A) of high Ga content. It is considered, therefore, that the tetrahedral GaO₄ incorporated into Ga-silicates (M) might have a lower symmetry than that incorporated into Ga-silicates(A). Further, the tetrahedral GaO₄ with low symmetry might be easily eluted from the silicate framework, because the amount of Ga elution from Ga-silicate(M) by treatment with HCl solution was greater than that from Ga-silicate(A) of high Ga content. Gallium-silicates(A) yielded more aromatic hydrocarbons from C₄H₁₀ than Ga-silicates (M) of high Ga content. It is concluded that the tetrahedral GaO₄ with lower symmetry might have a higher dehydrogenation activity.