Synthesis of La-hexaaluminate catalyst for methane combustion by a reverse SDS microemulsion

La-hexaaluminate catalyst for methane catalytic combustion was synthesized by a reverse microemulsion.Pseudo-ternary phase diagrams of a quaternary microemulsion system of sodium dodecyl sulfate (SDS),n-pentanol,n-octane,and water (or Al(NO3)3 solution) were presented.The effects of alcohol chain length,cosurfactant-to-surfactant ratio,and salt concentration on the formation and stability of the microemulsion system were studied.The phenomenon that the conductivity changed with water supported the phase behavior of the microemulsion system.La(Mnx/Fex)Al12-xO19-δcatalysts,applied in methane combustion and with high-temperature stability,were synthesized within the stable areas of the phase diagram of the microemulsion system,when SDS was chosen as surfactant,n-pentanol as cosurfactant,and n-octane as oil phase.The physical properties and structure of the catalysts were characterized by BET method,transmission electron microscope (TEM),and X-ray diffraction (XRD).A micro-fixed-bed reactor was used to measure the catalytic activity of hexaaluminates in methane combustion.The results show that the reverse microemulsions can be used to produce discrete La-hexaaluminate nanoparticles that display excellent methane combustion activity owing to their high surface area and high thermal stability.