Theoretical Study on PdCu/CeO2-Catalyzed Water-Gas Shift Reaction: Crucial Role of the Metal/Ceria Interface and O-2 Enhancement Effects

摘要

Low-temperature water-gas shift (LT-WGS) is an important process for H-2 production and purification. Recently, as promising LT-WGS catalysts, PdCu and PtCu bimetallic catalysts supported on ceria have been found. Existing studies showed that the addition of a small quantity of O-2 not only promoted CO conversion but also enhanced the production of H-2. In this study, by using density functional theory and microkinetic models, we investigated the reaction mechanisms of WGS reaction catalyzed by a PdCu/CeO2 catalyst and deciphered the underlying reasons for the O-2 enhancement phenomenon. We compared the catalytic performance of the unsupported PdCu metal to that of the PdCu/CeO2 interface structures and found that only the PdCu/CeO2 interface structure was active toward WGS. The unsupported metal was incapable of activating water, whereas the metal and ceria sites on the interface structure work in tandem to activate water and promote CO conversion. With the addition of OD WGS proceeded through a OH migration pathway, because O-2 modulated the oxidation state of the ceria support and increased the mobility of OH. The catalytic performance was quantitatively estimated using microkinetic models, and the results were consistent with previous experimental measurements. This study provides insights into the separate catalytic roles of different components in the PdCu/CeO2 system and corroborates the important roles of the metal/oxide interfaces in WGS reactions.