Studies On The Preparation Of Hexaaluminate Catalyts For Methane Combustion By Reverse Microemulsion Medium

The aim of this paper is to synthesis the hexaaluminate catalysts by the controble co-precipitation method with NH₄HCO₃ and NH4OH buffer solution as a prepitation agent, and reverse microemulsion medium for methane catalytic combustion application. Pseudo-ternary phase diagrams in quaternary microemulsion systems of cetyltrimethylammonium bromide (CTAB) [or sodium dodecyl sulfate (SDS)], w-butanol, n-octane and water [or Al(NO₃)₃. solution] were presented. The effects of alcohol chain length, ratio of surfactant to cosurfactant and salt concentration on the formation and stability of microemulsion system were studied. The catalysts of LaMe_xAl_12-xO_19-δ were synthesized with the optimal parameter in the phase diagrams of microemulsions systems. The performance and structure of the catalysts were characterized by BET, TG-DTA and XRD. The micro fix-bed reactor was used to measure the catalytic activities of catalysts to methane combustion. The results showed that the catalyst was successfully derived with chemical homogeneity both by using the buffer solution of NH₄HCO₃ and NH₄OH mixture as precipitation agent, and the microemulsion systems. The method of reverse microemulsion has more powerful on the reducing the formed temperature of the hexaaluminate crystallite, and just 950℃. The hexaaluminate substituted with Fe has high-catalytic activity and stability at high temperature, while that of Mn-substituted has higher catalytic activity at lower temperature. When cooperation of the Fe and Mn, (i.e. LaFeMnAl₁₀O_19+δ) exhibited a high surface area and catalytic activity to CH₄ combustion, the light-off temperature of CH₄ was only 475℃and the completely combustion temperature was 660℃.This is attributed to synergistic effect between Fe,Mn and La.