A novel type of reverse microemulsion system composed of water, i-propanol and n-butanol was developed as a reaction medium to prepare substituted-hexaaluminate La_0.95Ba_0.05MnAl₁₁O_19-α catalyst for methane combustion. The structure and properties of water in the novel reverse microemulsion system were investigated by means of ¹H NMR, FT-IR, electrical conductometry and laser light scattering apparatus. The electric conductivity of the novel reverse microemulsion system followed a nonlinear correlation when the volume fraction of water was low. There existed a critical point of φ^P (0.15) along the k～φ curve. ¹H NMR revealed that the chemical shift of the water proton signal moved to upfield with decreasing water content. FTIR showed that the ν_O-D band was shifted to higher frequency with increasing water concent. The size distribution of the Al(OH)₃ gel particles formed by hydrolysis of Al(i-OC₃H₇)₃ in the novel reverse microemulsion ranged from 226 to 329 nm with the average diameter of 267 nm. Substituted hexaaluminate La_0.95Ba_0.05MnAl₁₁O_19-α synthesized in the novel reverse microemulsion system possesses a surface area of 65 m²/g, comparable to 32 m²/g of similar samples prepared with pure water. XRD measurements revealed that β-Al₂O₃ was the only phase for this catalyst after calcination at 1200 ℃ for 10 h and its particle size measured by TEM is about 30 nm. This nanostructured hexaaluminate, when used as a catalyst for CH₄ combustion, allowed a light-off of a stream of 1% CH₄ in air at 420 ℃, as compared to 510 ℃ required for similar catalyst prepared with pure water. The excellent low-temperature catalytic activity of this catalyst arised from the formation of nanostrctured hexaaluminate that contained larger amount of manganese.

Key words: methane, catalytic combustion, reverse microemulsion, hexaaluminate, n-butanol, i-propanol