摘要
采用ＸＡＦＳ方法分别对Ｃｏ的近边结构和配位状态进行了详细的表征．ＸＡＮＥＳ的结果表明，所有样品中Ｃｏ均处于不对称的配位环境中，在吸收阈值处，形成了１ｓ→４ｐ吸收峰，并且该峰发生了分裂，尤其是Ｃｏ／γ－Ａｌ２Ｏ３分裂现象最为明显．对于Ｃｏ－Ｍ／γ－Ａｌ２Ｏ３（Ｍ＝Ｐｔ，Ｐｄ，Ｒｈ），这种不对称性可能来源于Ｃｏ的高度分散性及贵金属与Ｃｏ之间的相互作用，而对于Ｃｏ／γ－Ａｌ２Ｏ３，则与四面体配位的Ｃｏ２＋离子有关．ＥＸＡＦＳ结果表明，含贵金属样品中，Ｃｏ均以零价形式存在，和标样Ｃｏ粉相比，Ｃｏ－Ｃｏ键长略有增加，而配位数较标样下降许多．配位数的下降，表明Ｃｏ具有高度的分散性，而键长的增加可能是贵金属与Ｃｏ的相互作用削弱了Ｃｏ－Ｃｏ键引起的．
The paper (Ⅰ) has demonstrated the synergy effect between noble metals and cobalt phase, and has characterized the bulk and surface structure of the catalysts. In this paper (Ⅱ), XAFS method is used to characterize the structure of the catalysts. The result of XANES shows that except Co metal, all other standard compounds and catalysts have 1 s→4p absorption peak at Co K edge position (this peak is often called White Line). Before the main absorption peak, Co 3O 4 and CoAl 2O 4 have a weak absorption peak 1 s→3d . The main absorption peaks of all catalysts are split, particularly for Co/ γ Al 2O 3 catalyst. These phenomena prove that the cobalt is in the asymmetric coordination environment. For Co/ γ Al 2O 3, , the asymmetry is resulted from tetrahedrally coordinated Co 2+ ions, while for Co M/ γ Al 2O 3 (M=Pt, Pd, Rh), it maybe come from the highly dispersed cobalt metal and the interaction between noble metals and cobalt phase. The result of EXAFS shows that in Co M/ γ Al 2O 3 catalysts, Co exists as metal phase, but in Co/ γ Al 2O 3 catalyst, some cobalt exists as Co 2+ Al 3+ spinel. The length of Co-Co bond in Co M/ γ Al 2O 3 is a little longer than that in cobalt metal, but the coordination number decreases very much. This decrease shows that the cobalt is highly dispersed. The increase of Co-Co bond length may be related to the interaction between noble metals and cobalt metal.
出处
《催化学报》
CSCD
北大核心
1996年第3期193-196,共4页
基金
国家自然科学基金
关键词
钴
氧化铝
催化剂
铂
钯
铑
XAFS
Cobalt/ γ
Al 2O 3 catalyst
Platinum
Palladium
Rhodium
X ray absorption near edge structure
Extended X ray absorption fine structure
Synergy effect
