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Hydrothermal Synthesis of La-Mn-hexaaluminates for the Catalytic Combustion of Methane
Xu, Jinguang,Zhijian Tian,Wang, Junwei,Yunpeng Xu,Zhusheng Xu,Lin, Liwn 한국화학공학회 2003 Korean Journal of Chemical Engineering Vol.20 No.2
Hydrothermal synthesis by using urea hydrolysis at 1.0~3.0MPa and 120~130℃ was employed to prepare Mn-substituted hexaaluminate catalysts for methane combustion. The results from DTA-MS demonstrated that CO^2-_3 and OH^- anions co-exist in the hydrothermal reaction. XRD reveals that the components of carbonates of carbonates and hydroxides in the hydrothermal reaction are more favorable than those in the(NH_4)_2CO_3 co-precipitation for the formation of the Mn-substituted hexaaluminate phase. After calcination at 1,200℃ for 2h, LaMnAl_11O_19 is the major phase of the catalyst prepared by the hydrothermal synthesis method while LaAlO_3 is the major one of the catalysts prepared by NH_4OH and (NH_4)_2CO_3 co-precipitation. The catalyst prepared by hydrothermal synthesis has higher activity than that prepared by NH_4OH and (NH_4)CO_3 co-precipitation. The major reason is that more Mn^2+ ions have incorporated into the hexaaluminate lattice. The effect of drying methods on the formation of hexaaluminate phase was also discussed.