Preparation of β-Mo2C, Ni3Mo3N/β-Mo2C and its catalytic performance for methanation
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摘要: 通过焙烧钼酸铵和六次甲基四胺(HMT)生成的络合物,制备β-Mo2C。在此基础上加入Ni助剂制备了Ni3Mo3N/β-Mo2C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-Mo2C有较高的CO转化率,但CO转化率和CH4选择性分别从第10 h的75.93%和36.79%降低到了第100 h的67.41%和33.54%。因此,β-Mo2C活性不够稳定且CH4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CH4选择性分别从第10 h的83.15%和46.64%升高到了第100 h的92.51%和57.23%。这是因为Ni助剂的加入有助于生成Ni3Mo3N,新生成的Ni3Mo3N有利于甲烷化反应。Abstract: 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 (xCO), but xCO and selectivity of CH4 (sCH4) 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 sCH4 was low. The addition of Ni markedly promoted the catalyst activity and stability, xCO and sCH4 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.
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Key words:
- β-Mo2C /
- Ni3Mo3N /
- methanation
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图 2 催化剂的SEM照片
Figure 2 SEM images of the catalysts
(a): β-Mo2C; (b): Ni/β-Mo2C; (c): an enlarged image of β-Mo2C; (d): an enlarged image of Ni/β-Mo2C
图 3 催化剂的TEM和HRTEM照片
Figure 3 TEM and HRTEM images of the catalysts
(a): β-Mo2C; (b): Ni/β-Mo2C; (c): an enlarged image of β-Mo2C; (d): an enlarged image of Ni/β-Mo2C
图 4 CO转化率和CH4选择性随反应时间的变化
Figure 4 Change of CO conversion and CH4 selectivity along with the reaction time
(a): β-Mo2C; (b): Ni/β-Mo2C
表 1 催化剂的孔径结构和元素分析
Table 1 Pore structure and elemental analysis of the catalysts
Sample Specific surface area A/(m2·g-1) Pore volumev/(cm3·g-1) Average pore diameter d/nm Atom content w/% Moa Nia Cb Nb Hb Oc β-Mo2C 10.26 0.0399 15.57 89.08 - 7.52 0.15 0.07 3.18 Ni-Mo2C 6.49 0.0447 27.56 69.35 20.96 2.12 1.85 0.07 5.65 a: ICP-AES; b: elemental analysis; c: calculated by the subtraction 
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表 2 催化剂的甲烷化性能a,b
Table 2 Performance of different catalysts
Catalyst xCO/% Rate c/(mol·hcat-1·g-1) sCO2/% Selectivity of hydrocarbon product s/% sliquid/% CH4 C2H6 C2H4 β-Mo2C 67.41 1.85 38.34 33.54 16.15 4.34 7.63 Ni/β-Mo2C 92.51 3.09 32.71 57.23 1.83 0.11 8.12 a: reaction conditions: H2/CO(mol ratio)=2.0,p=3.0MPa,T=773K,GHSV= 4100h-1
b: time on stream: 100h
c: 2mL β-Mo2C 4.64g,2mL Ni/β-Mo2C 3.81g
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