尿素加入量对水热合成法制备Mn取代六铝酸盐催化剂的影响

采用以尿素水解为基础的水热合成法制备了Mn取代的镧六铝酸盐催化剂.研究了尿素加入量对所制备催化剂的化学组成、相结构、孔结构及甲烷催化燃烧活性的影响.n(尿素)/n(M+)(其中M+为带单位正电荷的金属离子)为1.0时,Mn2+离子沉淀不完全,所得催化剂甲烷催化燃烧活性较低.n(尿素)/n(M+)增加到2.0时,Mn2+离子沉淀完全,催化剂中六铝酸盐相增加,平均孔直径增大,甲烷催化燃烧活性提高.n(尿素)/n(M+)再增加至4.0时,比表面积降低,六铝酸盐相减少,平均孔直径降低,甲烷催化燃烧活性下降.n(尿素)/n(M+)为2.0时,所制备的催化剂在780℃及反应生成水蒸汽下运行100h,催化剂比表面积及甲烷燃烧活性都保持稳定.

Effect of Amounts of Urea on Mn-substituted Hexaaluminate Catalysts Prepared by Hydrothermal Synthesis

Mn-substituted hexaaluminate catalysts were prepared by hydrothermal synthesis based on hydrolysis of urea. The effects of amounts of urean(Urea)/ n(M+), M+ is metal cation with a single charge] added on chemical composition, phase, pore structure and methane combustion activity of the LaMnAl11O19-α catalysts were investigated. When n(Urea)/n(M+)=1.0, Mn2+ ions did not precipitated completely and the activity of the catalyst for methane combustion was low. With n(Urea)/ n(M+) ratio increasing to 2.0, the activity of catalyst was increased due to more amounts of hexaaluminate phase and larger pore diameter in the catalyst. With increasing of n(Urea)/n(M+) ratio further more, the activity of catalyst was decreased because amounts of hexaaluminate phase in the catalyst were decreased and the pore diameter of the catalyst became smaller. The life test during 100 h the catalyst prepared with n(Urea)/n(M+)=2.0 was carried out and the results showed that the activity of the catalyst for methane combustion and the specific surface area of the catalyst were maintained during 100 h life test.