甲烷部分氧化制合成气载体及助剂对Ni系催化剂活性的影响

Partial Oxidation of Methane to SyngasEffects of Support and Promoter on Catalytic Performance of Ni/A_2O_3 Catalyst

采用浸渍法制备了Ni系催化剂 ,并用程序升温还原和X射线衍射技术对催化剂进行了表征 ,用固定床微反装置考察了催化剂的催化活性 .活性考察结果表明 ,在Ni担载量为 8%的Ni/γ Al2 O3,Ni/δ Al2 O3,Ni/θ Al2 O3和Ni/α Al2 O3四种催化剂上 ,甲烷部分氧化制合成气反应的活性及产物选择性存在着明显的差异 .在 770℃下 ,甲烷转化率及CO和H2 的选择性按Ni/γ Al2 O3<Ni/δ Al2 O3<Ni/θ Al2 O3≈Ni/α Al2 O3顺序排列 .在相同的条件下 ,加入适量的CeO2 助剂后 ,Ni/γ Al2 O3和Ni/δ Al2 O3上的反应活性和选择性显著提高 ,而Ni/θ Al2 O3和Ni/α Al2 O3上的活性和选择性却变化不大 .同时 ,表征结果显示 ,Ni易与γ Al2 O3形成镍铝尖晶石NiAl2 O4,加入CeO2 助剂能有效地抑制该组分的生成 ,而Ni/α Al2 O3样品中未发现NiAl2 O4.因此 ,不同Ni/Al2 O3催化剂体系上的反应活性及选择性的差异可归结为不同结构Al2 O3载体的性质不同 ,及CeO2 对抑制镍铝尖晶石生成的效果不同 .

The Ni catalyst samples, with gamma-, delta-, theta-, or alpha -Al2O3 as a support and with CeO2 as a promoter, were characterized by TPR and XRD techniques, and evaluated by the reaction of partial oxidation of methane to syngas. The evaluation results showed that the catalytic activity of the catalyst samples and the product selectivity increase in the order of 8% Ni/gamma -Al2O3 < 8%Ni/<delta>-Al2O3 < 8%Ni/<theta>-Al2O3 approximate to8% Ni/alpha -Al2O3. When adding CeO2 promoter into the catalyst samples, the catalytic activity of 8% Ni/gamma -Al2O3 and 8% Ni/delta -Al2O3 increased significantly, while that of 8%Ni/theta -Al2O3 and 8% Ni/alpha -Al2O3 had hardly changed. This can be due to the depression of the formation of the low active crystalline phase NiAl2O4 when adding CeO2 promoter into 8% Ni/gamma -Al2O3 and 8% Ni/delta -Al2O3 samples. The characterization results from TPR and XRD confirmed the above viewpoint. For 8% Ni/theta -Al2O3 and 8% Ni/alpha -Al2O3 with low BET surface area, no crystalline phase NiAl2O4 was detected.