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本文探讨了在Ni-Mg-Al 水蒸气转化催化剂中稀土氧化物助剂CeO_2的作用。发现在催化剂的还原过程中,CeO_2与催化剂中的Ni、Al 之间发生了较强的相互作用,可以使Ni 与Ce 保持一定的比例,尤其是含CeO_2 3%的样品,其Ni/Ce 比在催化剂中的各个部位几乎不变。适量的CeO_2在Ni-Mg-Al 催化剂中有很强的分散作用,可使其中活性组分Ni 的晶粒度下降,分散度提高,表面组成均匀分布。但过量的CeO_2会与本体中的Al_2O_3形成CeAlO_3,导致催化剂结构的破坏,使分散度下降。另外,CeO_2的引入可使Ni-Mg-Al 催化剂在还原过程中产生迁移现象,使催化剂中各组分的分布更趋均匀。文中分析了导致迁移现象发生的可能原因。通过对含CeO_2样品的氧吸附性能研究,发现CeO_2本身存在有迁移性很强的晶格氧,它可在高温还原气氛中释放出来。根据CeO_2上述的这些作用与性能,提出了CeO_2对水蒸气转化过程的助催机理,由此可以解释它对催化剂活性和抗积炭性能有良好效果的原因。
In this paper, the role of rare earth oxide additive CeO_2 in Ni-Mg-Al steam reforming catalyst was discussed. It is found that there is a strong interaction between CeO 2 and Ni and Al in the catalyst during the reduction of the catalyst, which can keep a certain proportion of Ni and Ce, especially the sample containing CeO 2 3%, and the Ni / Ce ratio In the catalyst in various parts of almost unchanged. The proper amount of CeO 2 has a strong dispersion in the Ni-Mg-Al catalyst, which can decrease the grain size of the active component Ni, the dispersion degree of Ni and the surface composition of the CeO 2 uniformly distributed. However, excessive CeO 2 will form CeAlO 3 with Al 2 O 3 in the bulk, leading to the destruction of the catalyst structure and decreasing the degree of dispersion. In addition, the introduction of CeO 2 can make the migration of Ni-Mg-Al catalyst during the reduction process and make the distribution of the components in the catalyst more uniform. The paper analyzes the possible causes of the migration phenomenon. Through the study on the oxygen adsorption properties of samples containing CeO 2, it was found that CeO 2 itself has a highly migratory lattice oxygen, which can be released in high temperature reducing atmosphere. According to the above mentioned functions and properties of CeO 2, the promotion mechanism of CeO 2 to steam reforming process is proposed, which can explain the reason for its good effect on catalyst activity and anti-carbon deposition performance.