焙烧及还原温度对Ni-Mg甲烷化催化剂的影响

EFFECT OF CALCINATION AND REDUCTION TEMPERATURES ON Ni-Mg CATALYST FOR METHANATION

采用共沉淀-水热复合法制备Ni-Mg/Al2O3催化剂,考察焙烧和还原温度对其结构和甲烷化催化性能的影响,通过XRD,H2-TPR,TEM等表征,发现随焙烧温度升高,催化剂中NiAl2O4物相呈增多趋势,至900℃时,催化剂中镍物种完全以NiAl2O4形式存在,催化剂表面积从500℃焙烧的130m2/g降至900℃焙烧的34m2/g.针对600℃焙烧的催化剂,反应活性随还原温度升高呈现先增加后降低的趋势,其最佳还原温度为650℃,这主要是受Ni物种还原度、还原后Ni晶粒尺寸等多重因素影响.通过关联甲烷化性能与催化剂结构发现,NiO与载体之间相互作用适中,还原后表面能够形成较小的镍晶粒,催化剂具有较好的甲烷化活性和稳定性.

Ni-Mg/Al2O3 catalyst for syngas methanation was prepared by an approach combining co-precipitation and hydrothermal methods.The effect of calcination and reduction temperatures on catalyst structure and performance for methanation were investigated by activity evaluation and catalyst characterization using X-ray diffraction （XRD）,temperature-programmed H2 reduction （H2-TPR）,transmission electron microscopy （TEM） and so on.The results showed that with the increase in calcination temperature the reduction of the catalyst become more difficult because of the formation of NiAl2O4 at high temperatures,especially at temperatures above 900 ℃.The specific surface area of the catalyst decreased from 130 m2/g to 34 m2/g corresponding to the calcination temperatures rise from 500 ℃ to 900 ℃.After calcination at 600 ℃,the stability and catalytic activity of the catalyst first increased and then decreased with raising the reduction temperature,and the best methanation performance appeared at a reduction temperature of 650 ℃.This is due to the differences in the reductive degrees of nickel compounds and in the grain sizes of resulting Ni.It demonstrates actually the relationship between the catalytic performance for methanantion and the structure of the Ni-Mg/Al2O3 catalyst.This study clarified that for good catalytic performance of methanation,the grain size of Ni should be small and the interaction between active metal （Ni） and catalyst supporter （Al2O3） should be moderate.