Abstract: Mn-substituted hexaaluminate catalysts were prepared by hydrothermal synthesis based on hydrolysis of urea. The effects of amounts of urea[n(Urea)/ n(M⁺), M⁺ is metal cation with a single charge] added on chemical composition, phase, pore structure and methane combustion activity of the LaMnAl₁₁O_19-α catalysts were investigated. When n(Urea)/n(M⁺)=1.0, Mn²⁺ ions did not precipitated completely and the activity of the catalyst for methane combustion was low. With n(Urea)/ n(M⁺) ratio increasing to 2.0, the activity of catalyst was increased due to more amounts of hexaaluminate phase and larger pore diameter in the catalyst. With increasing of n(Urea)/n(M⁺) ratio further more, the activity of catalyst was decreased because amounts of hexaaluminate phase in the catalyst were decreased and the pore diameter of the catalyst became smaller. The life test during 100 h the catalyst prepared with n(Urea)/n(M⁺)=2.0 was carried out and the results showed that the activity of the catalyst for methane combustion and the specific surface area of the catalyst were maintained during 100 h life test.

Key words: Methane, Catalytical combustion, Hexaaluminate, Hydrothermal synthesis, Urea