In-Situ Extended X-Ray Absorption Fine Structure Study of Chemical Promoters in Catalysis

用扩展X射线吸收精细结构(EXAFS)研究了碱金属助剂与负载型Rh催化剂的相互作用。利用原位EXAFS池，可以观察还原催化剂和反应条件下碱金属和过渡金属原子的性质和多样性。这些数据与催化剂的原子吸收、X射线衍射、气体吸附、红外光谱和热脱附表征结果以及瞬时动力学研究相结合，确定了助剂和催化金属的成键、电子态、近邻和局部结构。通过添加少量助剂对催化剂进行化学改性可以极大地影响催化剂的活性和选择性。许多关于启动子如何发挥作用的基本问题仍然没有得到回答，包括它们位于表面的什么位置，它们与载体有什么关系，它们与反应物有什么相互作用。这些问题是使用EXAFS、瞬变动力学和更传统的技术相结合来解决的。这可能导致表面化学促进的一般理论。

The interaction of alkali-metal promoters with supported rhodium catalysts is studied using extended X-ray absorption fine structure (EXAFS). By use of an in-situ EXAFS cell, it is possible to observe the nature and diversity of the alkali-metal and transition-metal atoms both in the reduced catalysts and under reaction conditions. These data are combined with results of catalyst characterization by atomic absorption, X-ray diffraction, gas adsorption, infrared spectroscopy, and thermal desorption, as well as transient kinetic studies, on the same catalysts to define the bonding, electronic state, nearest neighbors, and local structure of both the promoter and the catalytic metal. Chemical modification of catalysts by the addition of small quantities of a promoter can greatly affect catalyst activity and selectivity. Many fundamental questions about how promoters function remain unanswered, including where they are located on the surface, what relationship they have with the support, and what interactions they have with the reactants. These questions are addressed using a combination of EXAFS, transient kinetics, and more traditional techniques. This could lead to a general theory of surface chemical promotion.