高温水热处理后Ni/a-Al_2O_3催化剂的镍分敏度对抗结碳性能的影响

THE INFLUENCE OF NICKEL DISPERSION ON RESISTANCE TO CARBON FORMATION OF Ni/d-Al_2O_3 CATALYSTS AFTER HYDROTHERMAL TREATMENT

本文研究了烃类蒸汽转化催化剂Ni/α-Al_2O_3 经高温水热处理(987K,H_2O/H_2 为7.5)后,平均镍晶粒度的变化及其对催化剂抗结碳性能的影响规律。实验证明,镍晶粒随水热处理时间的增加先是熔结长大,当水热处理足够长时间后,镍晶粒产生再分散。其积碳速率与镍晶粒大小的变化完全相适应。将La_2O_3 加入催化剂后可以显著提高镍在载体表面上的分散度,从而提高催化剂的抗碳性能。将La_2O_3和BaO同时加入Ni/α-Al_2O_3 催化剂时,在水热处理条件下所产生的 LaAlO_3和尖晶石结构的BaAl_2O_4,能促进金属颗粒在载体表面上的铺展,并阻止晶粒的熔结长大,使镍晶粒的再分散作用更为明显。

The change of average nickel crystallite size and its effect on the resistance to carbon formation of the Ni/α-Al2O3 steam reforming catalysts after hydrothermal treatment (987K, H2O/H2 = 7.5) were studied by TG and XRD. It was found that the nickel particles of the catalysts coalesce first with hydrothermal treatment and then redisperse. The rate of carbon deposition during steam reforming of n-heptane also varies correspondingly with the nickel crystallite size. The dispersion of nickel on the catalyst support modified by addition of La2O3 was obviously increased and the resistance to formation was also increased and the resistance to carbon formation was also enhanced. This can be attributed to the strong chemical interaction between metal and support and to the change in the interfacial free energy between metal and support. As an oxidizing agent, steam can enhance the wetting and spreading of the metal particles over the support surface. The further contraction and splitting of the surface film form some small particles. Because of La2O3 and BaO added to Ni/aaaaaaaa-Al2O3 catalysts, the metal/ support interface under the condition of hydrothermal treatment may promote spreading of nickel particles and red ise rsicn.