La取代Ba对Ba1-xLaxMn3Al9O19-α催化剂结构及甲烷催化燃烧性能的影响

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-xLaxMn3Al9O19-α).在Mn含量达到阈值时,研究了不同量的La取代Ba对Ba1-xLaxMn3Al9O19-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-γAl2O3反应生成LaAlO3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BaAl2O4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(-βAl2O3)相的形成.当x<0.4时,BaAl2O4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-xLaxMn3Al9O19-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.

Effect of La3+ Substituting Ba2+ on the Structure and Methane Combustion Activity of Ba1-xLaxMn3Al9O19-α Catalysts

Mn-substituted hexaaluminate(Ba1-xLaxMn3Al9O19-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 Ba1-xLaxMn3Al9O19-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 Ba1-xLaxMn3Al9O19-α catalysts.The methane combustion activity of the Ba1-xLaxMn3Al9O19-α catalysts varied with the change of x,and the(Ba0.2La0.8Mn3Al9O)19-α((x=0.8)) catalyst showed the highest activity for methane combustion.