Characterization of Rh Particles and Li-Promoted Rh Particles in Y Zeolite during CO_2 Hydrogenation-A New Mechanism for Catalysis Controlled by the Dynamic Structure of Rh Particles and the Li Additive Effect

摘要

The structure transformations of Rh particles in Rh ion-exchanged zeoltie catalysts (RhY) and in Li-doped RhY catalysts (Li/RhY) were studied by meansof EXAFS (extended X-ray absorption fine structure) in order to reveal the origin of the different CO_2 hydorgenation catalysts. CH_4 was mainly procued from CO_2 + H_2 on RhY, while CO was found on Li-doped RhY under similar reaction conditions. The geometric and electronic structure of Rh species in Y zeolite had litle difference between the two catalysts before the reaction. However, EXAFS revealted that the structures of Rh epecies under the reaction conditioons were quite different. During the reaction, we foudn disassenbly of Rh particles in RhY, while Rh particles were stably present in Li/RhY. We discuss teh different reaction mechanisms and catalytic properties of RhY and Li-doped RhY catalysts on the basis of their different dynamic structures which might be controlled by Li additive.