摘要
在一定实验条件下(焙烧温度<773K),NiO与γ-Al_2O_3之间发生强相互作用而使得Ni(Ⅱ)难以被H_2所还原.其实质是Ni(Ⅱ)进入了γ-Al_2O_3表面层上的四、六配位空位.按作者提出的掺入模型进行计算,实验也证实随着负载量增加表面空位均被Ni(Ⅱ)占据之后,过量NiO就以晶态附着在表面上.在有NiO晶相出现时,经873K以上高温处理,Ni(Ⅱ)、Al(Ⅲ)间的相互扩散导致在NiO微晶上形成类似非计量的NiAl_2O_4.扩散作用随预处理温度提高而加剧,最终形成结构较为完整的NiAl_2O_4尖晶石.与γ-Al_2O_3发生强相互作用的NiO也随之而增多.焙烧温度、负载量是影响相互作用的重要因素。
TPR, XRD and UV-DRS were used to characterize a series of NiO / γ-Al2O3 samples. The NiO loadings were varied from 1.0 to 40 wt%, and at least two distinct types of NiOspecies with apparently different reduction temperatures were observed.
When the calcination temperature was 773K, the incorporation of Ni( Ⅱ) ions into the surface vacant sites of the 110 plane of δ-Al2O3 was suggested to occur, and the dispersion capacity of these hihgly dispersed nickel oxide spesies, which have higher reduction temperature than bulk NiO in TPR was evaluated to be 9.8 × 1018 ions/m2, which was consistent with the experimental results. As the loadings of NiO were increased over this limit, NiO crystals similar to that of bulk phase nickel oxide were detected. In these cases, the counter diffusion of Ni( Ⅱ) and Al(Ⅲ) ions might occur during calcination.
For high loading samples, with the increasing of the calcination temperature (higher than 773K) the dispersion of NiO was increased due to the formation of NiAl2O4spinel. Apparently, both the loading amount of NiO and the calcination condition play important roles concerning the interaction between NiO and δ-Al2O3.
出处
《无机化学学报》
SCIE
CAS
CSCD
北大核心
1991年第1期122-127,共6页
Chinese Journal of Inorganic Chemistry
基金
国家自然科学基金资助项目
关键词
氧化镍
相互作用
载体
Γ-氧化铝
metal oxide-support interaction, dispersion capacity, NiO, γ-A1_2O_3
