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采用 X-射线吸收近边结构 ( XANES)和扩展 X-射线吸收精细结构 ( EXAFS)技术 ,对用不同原料盐和不同焙烧温度制得的 Co/γ- Al2 O3催化剂中钴的微观结构进行了详细的表征 .XANES结果表明 ,以硝酸盐为原料盐于50 0℃焙烧的样品 Co( N) - 50 0 ,其 Co- K边的近边结构与标样 Co3O4 相似 ,而其它样品的近边结构则与标样Co Al2 O4 相似 .随焙烧温度提高 ,在吸收边前的弱吸收峰 ( 1 s→ 3d)逐渐增强 ,在吸收阈值处 ,主吸收峰 ( 1 s→ 4p)的分裂变得更明显 .950℃焙烧的样品 ,在主吸收峰上升过程中出现了肩峰 ( 1 s→ 4s) .这些特征表明 ,样品中钴主要以 Co2 + 离子形式存在 ,钴离子与载体作用的加强 ,使非化学计量的尖晶石相在结构上与化学计量的 Co Al2 O4 越来越接近 .EXAFS结果表明 ,样品 Co( N) - 50 0中 ,钴主要以 Co3O4 的形式存在 .其第一配位壳层 Co- O配位数明显低于标样 Co3O4 ,说明该相具有较高的分散性 .其它所有样品中 ,钴主要以非化学计量的尖晶石相存在 ,其第一配位壳层 Co- O配位数随焙烧温度从 50 0℃提高至 950℃ ,与标样 Co Al2 O4 越来越接近 ;相同焙烧温度下 ,从醋酸钴制得的 Co( A)系列样品更容易形成 Co- Al尖晶石相 .XANES和 EXAFS结果很好地说明了前文 [7] 中样品对 CO氧化和乙烯选?
The microstructure of Co in the Co / γ-Al 2 O 3 catalyst prepared with different raw materials and different calcination temperatures was investigated by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) The XANES results show that the Co (N) - 50 0 sample with nitrate as raw material calcined at 500 ℃ has a similar structure near the Co-K side as the standard sample Co3O4, The structure is similar to that of the standard sample Al 2 O 4, and the weak absorption peak (1 s → 3d) before the absorption edge gradually increases with increasing the calcination temperature. At the absorption threshold, the main absorption peak (1 s → 4p) (1s → 4s) appeared during the ascending of the main absorption peak.These samples showed that cobalt mainly existed in the form of Co2 + ions and the interaction between cobalt ions and the supporter was enhanced, The non-stoichiometric spinel phase is structurally closer to the stoichiometric Co Al 2 O 4.The results of EXAFS show that the Co (N) - 50 0 mainly exists as Co 3 O 4 in the sample Co The Co-O coordination number of bit shell is obviously lower than that of standard sample Co3O4, indicating that this phase has In all other samples, cobalt is mainly present in the non-stoichiometric spinel phase, the Co-O coordination number of the first coordination shell increases from 50 0 ℃ to 950 ℃ with the calcination temperature, Co Al 2 O 4 is getting closer and closer. Co-Al spinel phase is more easily formed from Co (A) series sample prepared from cobalt acetate at the same calcination temperature.The results of XANES and EXAFS are well explained in [7] In the sample of CO oxidation and ethylene election?