Structure–Activity Relationships of Copper- and Potassium-Modified Iron Oxide Catalysts during Reverse Water–Gas Shift Reaction
Mengwei Gu, Sheng Dai, Runfa Qiu, Michael E. Ford, Chenxi Cao, Israel E. Wachs, Minghui Zhu
Abstract
The reverse water–gas shift (RWGS) reaction is an initial and essential step for CO2 hydrogenation. In this study, Cu- and K-modified iron oxide catalysts were investigated with a series of in/ex-situ characterization techniques, including in situ XRD, in situ Raman, in situ DRIFTS quasi in situ XPS, quasi in situ HS-LEIS, H2-TPR, CO2-TPD, and TPSR. The surface structure of the catalyst is found to strongly depend on the presence of Cu and K, leading to diverse reducibility and basicity. Adding K to the iron-based catalyst alters the reaction from a redox pathway that proceeds on surface redox sites to an associative pathway that proceeds on surface redox and basic sites. Metallic Cu facilitates hydrogen dissociation and promotes both mechanisms by either boosting surface vacancy sites or supplying abundant surface hydrogen atoms. These findings would be beneficial for the rational design of CO2 hydrogenation catalysts.