Preparation Of Substituted La-Hexaaluminate By Reverse Microemulsion And Investigation Of Its Catalytic Performance

Temperature of the traditional combustion of methane is very high leading to pollution of the environment. Catalytic combustion is effective method to control and eliminate NOx with high combustion efficiency and energy utilization. Industrialization of catalytic combustion of methane is restricted by the performance of catalysts. Reverse microemulsion is a new and potential synthesis technology for the preparation of nano-particles, and also can improve the performance of nano-materials. Using reverse microemulsion as media, series of metals substituted La, SrLa-hexaaluminate catalysts have been synthesized by RP-microemulsion-coprecipitation method in system of water (solution)/Triton X-100/ n-hexanol/cyclohexane. The effects of synthesis conditions and substituted elements on phase, structure and specific surface area have been investigated by XRD, XPS, BET and SEM characterization. Catalytic activity of hexaaluminate has also been tested by catalytic combustion of methane. Main conclusions are as follow: Reverse microemulsion system of water/Triton X-100/n-hexanol / cyclohexane is capable of forming nano-uniform distribution of hexaaluminate, and can make the hexaaluminate crystal form at lower temperature 1100℃.The radius of metal has great influence on the phase of hexaaluminate. The radius of Mn³⁺ and Fe³⁺ are similar to Al³⁺, easier access hexaaluminate skeleton and promote the formation of pure single heaaluminate phase. For Ni, Mg, Cu, Co and Y, with the increase of ionic radius are difficult to enter hexaaluminate skeleton, incorporation of Mn and Fe leads to another phase formation.XPS showed that in the Mn substituted Hexaaluminate, the oxidation states of Mn are Mn²⁺ and Mn³⁺, and Fe ions are mainly exist in form of Fe³⁺.The specific surface areas of catalysts decrease with the increase of Mn substitute content. The introduction of single Mn could improve the catalytic activity at low temperature and make methane light-off temperature shift to lower value, Single Fe could make methane completely convert at lower temperature; Fe and Mn substituted had the highest activity at both low temperature and high temperature. The stability of LaMnFeAl₁₀ O¹⁹ at high temperature is also excellent.Catalytic activity for methane combustion has been measured for La-and La_0．5 Sr_0．5 -hexaaluminate, among single metal substituted hexaaluminates, the highest activity was obtained by catalysts of LaMnAl₁₁ O₁₉ and La_0．5 Sr_0．5 Mn_1．5 Al_10．5 O₁₉ , composite metal substituted LaMnFeAl₁₀ O₁₉å’ŒLa_0．5 Sr_0．5 MnFeAl₁₀ O₁₉ have the most excellent performance.