A comprehensive theoretical study on CuOx/Cu(110) catalyzed water–gas shift reaction

In recent years, theoretical studies on Cu-based catalysts for the water–gas shift reaction (WGSR) have been conducted extensively. However, the issues concerning the oxidation state of copper atoms under reaction conditions and their roles in catalyzing WGSR remain unresolved. Surface science experiments have demonstrated that clean Cu(110) exhibits higher catalytic activity than clean Cu(111), and a previous study has theoretically indicated that the oxidation can enhance the intrinsic activity of Cu(111). Therefore, determining the surface oxides on Cu(110) and their catalytic activity is fundamental and will provide valuable insights for rational catalyst design. In this paper, ab initio atomistic thermodynamics was performed to reveal the potential phase transitions from clean Cu(110) to Cu₂O (110), including added row-(4 × 1) (AR-41), added row-(2 × 1) (AR-21), as well as added strand-c(6 × 2) (AS-c62) structures. The WGSR mechanisms were systematically investigated on these distinct surfaces by density functional theory (DFT) calculations. Additionally, we identified a volcano-type relationship between the catalytic performance and the oxidation degree of Cu(110), with the mildly oxidized AR-41 structure exhibiting optimal activity, as determined by mean-field microkinetic modeling (MF-MKM) and kinetic Monte Carlo (kMC) simulations. Moreover, the degree of rate control (DRC) analysis revealed that water dissociation is no longer the rate-determining step for oxidized structures compared to clean Cu(110). Instead, the direct oxidation of CO and the production of H₂ may play a more critical role in CuO_x/Cu(110)-catalyzed WGSR. Meanwhile, it was found that the redox and carboxyl mechanisms compete with each other. The carboxyl mechanism predominantly operates at low levels of oxidation, while the redox mechanism takes precedence at high levels of oxidation. Consequently, the appropriate oxidation state will enhance catalytic activity on Cu(110). Additionally, doping with other metal atoms was used as a strategy to improve catalyst performance, and it was found that doping with Pd or Zn may slightly promote the catalytic performance. Furthermore, a comparison between CuO_x/Cu(110) and CuO_x/Cu(111) was conducted, and it was found that they show different catalytic activity due to their unique interfaces of CuO_x and metallic subsurface.