【摘要】 采用以尿素水解为基础的水热合成法制备了La和Mn取代的六铝酸盐催化剂(Ba1-xLaxMn3A l9O19-α).在Mn含量达到阈值时,研究了不同量的La取代Ba对Ba1-xLaxMn3A l9O19-α的相组成、结构、热稳定性及甲烷催化燃烧活性的影响.当x≥0.4时,水热合成过程中生成的La2(CO3)3在530~580℃分解,800~900℃时与-γA l2O3反应生成LaA lO3钙钛矿相,可抑制由BaCO3分解而生成的Ba2+的固相扩散,从而阻止了BaA l2O4尖晶石相的生成,使Ba2+在固相中保持较高的分散性,促进了六铝酸盐(-βA l2O3)相的形成.当x<0.4时,BaA l2O4尖晶石相的存在引起催化剂比表面积和催化燃烧活性的降低.La3+取代Ba2+后,六铝酸盐结构发生一定程度的扭变.这种扭变越大,所形成的六铝酸盐催化剂的热稳定性越差.Ba1-xLaxMn3A l9O19-α催化剂的甲烷催化燃烧活性随x的增大而增加,x=0.8时催化剂的活性最佳.更多还原

【Abstract】 Mn-substituted hexaaluminate(Ba_1-xLa_xMn₃Al₉O_19-α) catalysts were prepared by hydrothermal synthesis based on hydrolysis of urea.Effect of La³⁺ substituting Ba²⁺ on phase compositions,structure,thermal stability and methane combustion activity was investigated.When x≥0.4,La₂(CO₃)₃ decomposed in the range of 530—580 ℃ to be converted into La₂O₃.La₂O₃ reacted with γ-Al₂O₃ to form LaAlO₃ perovskite phase in the temperature range of 800—900 ℃.BaAl₂O₄ spinel phase was suppressed due to the formation（of LaAlO）₃perovskite phase,and higher dispersing of Ba²⁺ in the solid phase was maintained,which is（more favorable） for the formation of hexaaluminate phase.When（x<0.4）,the BET specific surface areas（and methane） combustion activities of the Ba_1-xLa_xMn₃Al₉O_19-α catalysts decreased due to the formation of(BaAl₂O)₄（spinel phase）.The hexaaluminate structure distorted to some extent when Ba²⁺ were substituted with La³⁺.（The larger） the distortion,the lower the thermal stability of the Ba_1-xLa_xMn₃Al₉O_19-α catalysts.The methane combustion activity of the Ba_1-xLa_xMn₃Al₉O_19-α catalysts varied with the change of x,and the(Ba_0.2La_0.8Mn₃Al₉O)_19-α（（x=0.8）） catalyst showed the highest activity for methane combustion.更多还原