Preparation Of Doped Hexaaluminate Catalyts By Reverse Microemulsion And Investigation Of Its Catalytic Performance

Catalytic combustion is considered as a promising method for enhancing efficiency of the natural gas combustion with minimum emissions of NO_X. The performance of the catalysts is the key factor in industry application of the natural gas catalytic combustion technology. The reaserch issue of the hexaaluminate catalysts is the to find advanced catalysts, which possess with high thermal ststability and high reaction activity.Reverse microemulsion is a promising solid catalysts synthesis technoloy for the preparation of nano-particles. Pseudo-ternary phase diagrams in quaternary microemulsion systems of Polyethylene glycol 200(PEG200), n-propanol, isooctane and water were drawed. The effects of cosurfactant's content, ratio of surfactant to cosurfactant, salt concentration and temperature on the formation and stability of microemulsion system were studied. The results showed that components and the component proportion have an important influence on the formation of the W/O microemulsion. Temperature also had an obvious effect on microemulsion formation. The ratio of surfactant to cosurfactant equaling 1/12 is the ideal synthesis condition of microemulsion at 25℃.The results on synthesizing reverse microemulsion composed of water/Span60-Tween80/n-butanol/isooctane showed that the ratio of surfactant to cosurfactant equaling 1/6 is the ideal synthesis condition of microemulsion at 40℃.Using reverse microemulsion as media, series of metals doped LaBa, LaSr-hexaaluminate catalysts were synthesized with the optimal parameter in the phase diagrams. The effects of Mn-, Co-, Fe-substitution on specific surface, structure and catalytic activity for methane combustion was investigated over heaaluminate catalysts through XRD, TPR and BET characterization.The hexaaluminate doped with Mn has hign-catalytic activity and stability at high temperature, while that of Co-doped has higher catalytic activity at lower temperature. When cooperation of the Mn and Co,(i.e.LaBaCoMnAl₁₀O₁₉) exhibited a higher catalytic activity to CH₄ combustion, the light-off temperature of CH₄ was only 454℃and the completely combustion temperature was 653℃. This is attributed to synergistic effect between Co and Mn.Catalytic activity for methane combustion has been measured for the series of La_0.2Sr_0.8Fe_xCo_2-x-hexaaluminate. With the increase of Fe substitute content, the highest activity was obtainde for catalysts La_0.2Sr_0.8Fe_0.4Co_1.6Al₁₀O₁₉, the light-off temperature of CH₄ was only 445℃and the completely combustion temperature was 663℃.