反应条件下的水蒸气处理对复合氧化物催化剂甲烷催化燃烧的影响

EFFECT OF STEAM ON THE STRUCTURE AND ACTIVITY OF COMPLEX OXIDE CATALYSTS FOR CH_4 COMBUSTION

对水热法制备的LaMnAl11O19-α(LMA)催化剂和微乳液法制备的Ce0 .5Ba0 .5MnAl11O19-α(CBMA)催化剂进行了 10 0h的甲烷催化燃烧活性试验 ,考察了反应条件下的水蒸气处理对催化剂的结构和甲烷催化燃烧活性的影响。结果表明 :反应条件下的水蒸气处理促进了水热法制备的LMA催化剂中的六铝酸盐相晶粒长大 ,比表面积降低 ,从而引起活性下降。对微乳液法制备的CBMA催化剂 ,反应条件下的水蒸气处理使得催化剂中的γ -Al2 O3转化为α -Al2 O3从而引起比表面积的大幅度降低 ,但催化活性没有出现明显变化 ,仍保持着较高的甲烷燃烧活性。

The LaMnAl 11 O 19-α and Ce 0.5 Ba 0.5 MnAl 11 O 19-α catalysts were prepared by the hydrothermal synthesis and reverse microemulsion method, respectively. The effects of structure and activity of CH 4 catalytic burn of both catalysts by steam treatment in the reaction conditions were inspected.Durability of the catalysts was tested using a gas mixture containing 1 vol% CH 4 at the catalyst bed temperature of about 760℃ after CH 4 combustion. The tests were carried out for 100 hours. The CH 4 conversion was above 99% for Ce 0.5 Ba 0.5 MnAl 11 O 19 α catalyst while it decreased from 100% to 92.3% for LaMnAl 11 O 19 α catalyst. The BET surface area of the LaMnAl 11 O 19 α catalyst was decreased from 39.6m 2.g 1 to 22.9 m 2.g 1 due to sintering of hexaaluminate phase. A drastic decrease in the surface area (from 136.4 m 2.g 1 to 51.4m 2.g 1 ) was observed for the Ce 0.5 Ba 0.5 MnAl 11 O 19 α catalyst due to the conversion of γ-Al 2O 3 phase in the catalyst to α-Al 2O 3 phase. However,the structure of CeO 2 did not change obviously.It is the major reason why the Ce 0.5 Ba 0.5 MnAl 11 O 19 α catalyst sustained high activity for CH 4 combustion.