Pengfei Wang, Guoquan Liu, Zhifei Hao, He Zhang, Yi Li, Wenming Sun, Lirong Zheng, and Sihui Zhan

PNAS; February 14, 2023; 120 (8) e2216584120

Significance

The use of oxide-supported isolated Pt single atoms as catalytic active sites is of interest due to their maximum atom utilization efficiency and unique catalytic properties for the removal of NO_x. However, relationships between the structure of active center, the dynamic response to environments, and catalytic functionality have proved difficult to experimentally establish. This research reveals that the in situ formation of adjacent cocatalytic sites boosts single-atom catalysts for the conversion of NO_x during the catalytic reaction of NO_x reduction with H₂. The presence of cocatalytic sites tunes and optimizes the catalytic performance at the atomic scale that can benefit the environment and human health by removing NO_x efficiently.

Abstract

Nitrogen oxide (NO_x) pollution presents a severe threat to the environment and human health. Catalytic reduction of NO_x with H₂ using single-atom catalysts poses considerable potential in the remediation of air pollution; however, the unfavorable process of H₂ dissociation limits its practical application. Herein, we report that the in situ formation of Pt_Ti cocatalytic sites (which are stabilized by Pt–Ti bonds) over Pt₁/TiO₂ significantly increases NO_x conversion by reducing the energy barrier of H₂ activation. We demonstrate that two H atoms of H₂ molecule are absorbed by adjacent Pt atoms in Pt–O and Pt–Ti, respectively, which can promote the cleave of H–H bonds. Besides, Pt_Ti sites facilitate the adsorption of NO molecules and further lower the activation barrier of the whole de-NO_x reaction. Extending the concept to Pt₁/Nb₂O₅ and Pd₁/TiO₂ systems also sees enhanced catalytic activities, demonstrating that engineering the cocatalytic sites can be a general strategy for the design of high-efficiency catalysts that can benefit environmental sustainability.

See https://www.pnas.org/doi/10.1073/pnas.2216584120

Figure 1: HAADF-STEM characterization of Pt₁/TiO₂. (A and E) HAADF-STEM images of fresh Pt₁/TiO₂ (A) and used Pt₁/TiO₂ (E). (B–D) In situ HAADF-STEM images and relevant intensity profiles of Pt₁/TiO₂ without reaction in Ar atmosphere at 125 °C (1 bar). (F–H) In situ HAADF-STEM images and relevant intensity profiles of Pt₁/TiO₂ under the reaction at 125 °C (NO:H2 ~ 1:1, 1 bar). (I–L) EDS mapping of used Pt₁/TiO₂. (M and N) The intensity profiles obtained in A and E, respectively.