CaxLa1-xMnAl11O19 六铝酸盐催化剂上甲烷的催化燃烧

以共沉淀法制备了CaxLa1-xMnAl11O19系列六铝酸盐催化剂,考察了Ca2 部分取代La3 对LaMnAl11O19六铝酸盐的甲烷催化燃烧活性和稳定性的影响以及活性与物理化学性能的关系,用X射线衍射、N2吸附、程序升温还原和透射电镜对其进行了表征.结果表明,当Ca2 加入量过高时,Ca2 不能进入到六铝酸盐骨架中,过量的Ca2 形成CaAl4O7杂相.当x=0.2时,催化剂活性最高,起燃温度为723 K,也提高了样品的热稳定性,1 373 K煅烧后比表面积为26.1 m2/g.Ca2 的加入使六铝酸盐晶粒变薄,这使材料的抗烧结性能增强,比表面积增大,同时Ca2 部分取代La3 使活性Mn3 的含量增加,这两方面的综合作用使得催化剂活性显著提高.对Sr2 ,Ca2 和K 部分取代La3 的六铝酸盐的比较实验结果表明,Ca2 部分取代La3 的样品具有最低的起燃温度.

Catalytic Combustion of Methane on CaxLa1-xMnAl11O19 Hexaaluminates

The effects of calcium substitution for lanthanum on the catalytic activity and stability of CaxLa1-x-MnAl11O19 hexaaluminate catalyst prepared by co-precipitation were investigated.The samples were characterized by X-ray diffraction,N2 adsorption,temperature-programmed reduction,and transmission electron microscopy(TEM).It was observed that Ca could not be totally incorporated into the hexaaluminate lattice for a high doping amount(x=0.8).In this case,a separate CaAl4O7 phase was formed.Ca0.2La0.8MnAl11O19 possessed the best catalytic activity with light-off temperature of 723 K and the highest BET surface area of 26.1 m2/g after calcination at 1 373 K.The TEM results revealed that the substitution of La3 by Ca2 led to a thinner hexaaluminate planer crystal,which improved the sintering resistance,increased the surface area,and raised the amount of reactive Mn3 species and the reducibility of the hexaaluminate.The enhanced catalytic activity was attributed to the combined effect of higher specific surface area and Mn3 content.Compared to Sr2 -and K -substituted La-hexaaluminates,the Ca2 -substituted samples demonstrated the lowest light-off temperature in methane combustion.