La取代Ba对Ba_(1-x)La_xMn_3Al_9O_(19-α)催化剂结构及甲烷催化燃烧性能的影响

Effect of La^(3+) Substituting Ba^(2+) on the Structure and Methane Combustion Activity of Ba_(1-x)La_xMn_3Al_9O_(19-α) Catalysts

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.

Mn-substituted hexaaluminate （ Ba1 -x Lax Mn3 A19 O19-α ） catalysts were prepared by hydrothermal synthesis based on hydrolysis of urea. Effect of La^3 ＋ substituting Ba^2＋ 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 LaAlO3perovskite phase, and higher dispersing of Ba^2＋ 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-x Lax Mn3Al9O19-α catalysts decreased due to the formation of BaAl2O4spinel phase. The hexaaluminate structure distorted to some extent when Ba^2＋ were substituted with La^3 ＋. The larger the distortion, the lower the thermal stability of the Ba1 -x Lax Mns Al9 O19-α catalysts. The methane combustion activity of the Bal_ La Mn3Al9O19-α catalysts varied with the change of x, and the Ba0.2La0.8Mn3Al9O19-α （x = 0. 8） catalyst showed the highest activity for methane combustion.