β-Mo_2C和Ni_3Mo_3N/β-Mo_2C的制备及其甲烷化反应性能研究

通过焙烧钼酸铵和六次甲基四胺(HMT)生成的络合物,制备β-Mo_2C。在此基础上加入Ni助剂制备了Ni_3Mo_3N/β-Mo_2C双金属碳化物催化剂。采用XRD、SEM、HRTEM、低温氮吸附、元素分析等方法对催化剂进行了表征,考察了其合成气甲烷化反应性能。结果表明,β-Mo_2C有较高的CO转化率,但CO转化率和CH_4选择性分别从第10h的75.93%和36.79%降低到了第100h的67.41%和33.54%。因此,β-Mo_2C活性不够稳定且CH_4选择性较低。而Ni助剂的加入显著提高了催化剂的甲烷化活性及稳定性,使CO转化率和CH_4选择性分别从第10h的83.15%和46.64%升高到了第100h的92.51%和57.23%。这是因为Ni助剂的加入有助于生成Ni_3Mo_3N,新生成的Ni_3Mo_3N有利于甲烷化反应。

Preparation of β-Mo2C,Ni3Mo3N/β-Mo2C and its catalytic performance for methanation

A complexes was produced using hexamethylenetetramine(HMT) as the complexing agent of ammonium molybdate, and β-Mo₂C was prepared by a simple thermal decomposition of this complexes. And then Ni was introduced and the bimetallic carbide Ni₃Mo₃N/β-Mo₂C was prepared. The as-prepared products were characterized by XRD, low-temperature nitrogen adsorption, SEM, HRTEM, element analysis (EA), and the performances of the prepared catalysts for methanation were investigated. The results showed that the bulk molybdenum carbide exhibited high conversion of CO (x_CO), but x_CO and selectivity of CH₄ (s_CH4) on β-Mo₂C decreased from 75.93% and 36.79% to 67.41% and 33.54% within 100 h. Thus the catalytic activity was not stable and s_CH4 was low. The addition of Ni markedly promoted the catalyst activity and stability, x_CO and s_CH4 on Ni₃Mo₃N/β-Mo₂C increased from 83.15% and 46.64% to 92.51% and 57.23% within 100h, which should be attributed to the newly produced Ni₃Mo₃N after Ni addition.