载体织构对Ni-Fe/γ-Al2O3催化剂结构和甲烷化活性的影响

摘要

Ni-Fe/γ-Al2O3 catalysts with four different γ-Al2O3 supports were prepared by incipient impregnation and characterized by XRD, BET and H2-TPR. Catalytic behaviors of the catalysts for low-temperature CO methanation were investigated in a slurry reactor. The results showed that the surface texture properties of γ-Al2O3 supports had great impact on distribution of Ni reactive species and methanation activity. Moderate specific surface area (192m2/g) and pore size (5.8 nm) of γ-Al2O3 was favor for the dispersion of active component, resulting in a higher amount of β-NiO and smaller Ni crystal particle size, which increased active sites, thus having better methanation activity and stability, with a CO conversion of 97.0% and a CH 4 selectivity of 89.0%. However, the catalyst prepared by high silica γ-Al2O3 support with larger specific surface area contained a great amount of α-NiO, which was inclined to agglomerate in the reduction process, resulting in low catalytic activity and stability, with a CO initial conversion of 85.5%and rapid deactivation after 17 hours.%采用等体积浸渍法制备了4种不同γ-Al2O3为载体的负载型Ni-Fe/γ-Al2O3催化剂，通过BET、XRD和H2-TPR等表征手段对载体和催化剂进行了表面微观结构分析，并考察了其低温浆态床催化CO甲烷化反应的活性和稳定性。结果表明，载体γ-Al2O3的表面织构性质对Ni-Fe/γ-Al2O3催化剂活性物质Ni的分布和甲烷化活性影响较大。比表面积和平均孔径分别为192m2/g和5.8nm的γ-Al2O3载体具有较好的低温浆态床CO甲烷化活性，有利于活性组分的分散，且与γ-Al2O3表面作用较强的β-NiO含量较多，还原后活性物质Ni晶粒较小，形成的活性中心数量多，甲烷化活性及稳定性较好，CO的平均转化率和CH4平均选择性分别达到97.0%和89.0%。而以比表面积较大的高硅γ-Al2O3载体制备的催化剂，游离态α-NiO含量较多，还原过程中容易迁移和团聚，形成较大的Ni晶粒，催化剂的活性和稳定性均差，CO的初始转化率为85.5%，反应17h后活性急剧下降。