In-situ XAFS Analysis of the Catalysts under Reaction Conditions

Abstract

Recently in-situ XAFS analysis of the catalysts under reaction conditions has widely been performed together with synchrotron radiation light sources of the 2nd−3rd generation. In some cases this method requires time-resolving analytical techniques such as DXAFS and QXAFS. In addition, design of the in-situ cell is crucial for obtaining spectra which properly reflect the structures of the catalysts under reaction conditions. Two kinds of in-situ cells designed for experiments under high-pressure conditions are presented. Four of recent works are reviewed: Observation of Mo suboxide species during reduction of MoO₃, Cu⁺ species formed in Cu-ZSM-5 during reduction process, structural change of Cu metal particles on Cu/ZnO under various reaction conditions, and Rh species during CO₂ hydrogenation. Intermediate species appearing in the course of chemical reactions have very short lives, therefore continuous observation of surface species by in-situ method is indispensable for detection of such species. Moreover, the in-situ method is the only way to obtain the structure of catalysts under the reaction conditions.