Characterization of Rh particles and Li-promoted Rh particles in Y zeoliteduring CO2 hydrogenation - A new mechanism for catalysis controlled by thedynamic structure of Rh particles and the Li additive effect

The structure transformations of Rh particles in Rh ion-exchanged zeolite c atalysts (RhY) and in Li-doped RhY catalysts (Li/RhY) were studied by means of EXAFS (extended X-ray absorption fine structure) in order to reveal the origin of the different CO2 hydrogenation catalyses of the two catalysts. CH4 was mainly produced from CO2 + H-2 on RhY, while CO was found on Li-dop ed RhY under similar reaction conditions. The geometric and electronic stru cture of Rh species in Y zeolite had little difference between the two cata lysts before the reaction. However, EXAFS revealed that the structures of R h species under the reaction conditions were quite different. During the re action, we found disassembly of Rh particles in RhY, while Rh particles wer e stably present in Li/RhY. We discuss the different reaction mechanisms an d catalytic properties of RhY and Li-doped RhY catalysts on the basis of th eir different dynamic structures which might be controlled by Li additive. (C) 2000 Academic Press.