稀土Ce对制合成气用Ce-Ni/Al_2O_3催化剂活性和稳定性的影响

Effect of Ce Promoter on Activity and Stability of Ce-Ni/Al_2O_3 in Partial Oxidation of Methane and CO_2 Reforming of Methane to Syngas

用浸渍法制备了Ni/Al2 O3 和Ce Ni/Al2 O3 催化剂 ,并用BET ,TGA DTA和XPS技术对催化剂进行了表征 ,考察了稀土Ce对催化剂性能的影响 ,探讨了催化剂失活的原因 .结果表明 ,在甲烷部分氧化和二氧化碳重整反应中 ,稀土Ce存在有部分还原变价过程 (Ce4+ →Ce3 + ) ,不仅抑制了催化剂的积碳 ,而且改善了催化剂的水热稳定性和催化性能 .经过较长时间反应的Ce Ni/Al2 O3 催化剂 ,其比表面积下降 ,活性物种Ni和助剂Ce向体相迁移或部分流失 。

Partial oxidation of methane and CO2 reforming of CH4 to syngas over Ce-Ni/Al2O3 catalyst were studied in a continuous-flow fixed-bed reactor. Before the reaction, 0.2 g catalyst (20 similar to 40 mesh) was firstly heated to 750 degreesC under H-2 stream (30 ml/min) and maintained for 0.5 h, then the reactants (SV = 52.2 L/(g.h)) were introduced into the reactor. The reaction was carried out at 750 degreesC, and the outlet gases were analyzed by GC with TCD and a TDX-01 column (2 m). The effect of Cc promoter on the activity and stability of the catalyst was studied by BET, TGA-DTA and XPS techniques. The results showed that the addition of Ce into Ni/Al2O3 increased remarkably the conversion of CH4 and CO2 by 33%. On the other hand, the reduction of Ce4+ to Ce3+ during the reaction was beneficial to carbon deposit-resistance oil the surface of the catalyst, thus the addition of Ce greatly improved the catalyst stability in the presence of vapor. It was shown that Ni and Ce gradually migrated into the bulk phase of the catalyst during the reaction, leading to the decrease of Ni and Ce on the surface of the catalyst. Meanwhile the loss and sintering of Ni were found at higher reaction temperature. These results indicated that the decrease of the specific surface area, as well as the partial loss and sintering of Ni on the surface of the catalyst during the reaction may be responsible for the decrease of the catalyst activity.