A promising single atom catalyst for CO oxidation: Ag on boron vacancies of h-BN sheets.

Zhansheng Lu,Shuo Li,Dongwei Ma,Ruqian Wu,Peng Lv,Zongxian Yang

doi:10.1039/c7cp02430d

Abstract

Single atom catalysts (SACs) have attracted broad research interest in recent years due to their importance in various fields, such as environmental protection and energy conversion. Here, we discuss the mechanisms of CO oxidation to CO2 over single Ag atoms supported on hexagonal boron-nitride sheets (Ag1/BN) through systematic van der Waals inclusive density functional theory (DFT-D) calculations. The Ag adatom can be anchored onto a boron defect (VB), as suggested by the large energy barrier of 3.12 eV for Ag diffusion away from the VB site. Three possible mechanisms (i.e., Eley-Rideal, Langmuir-Hinshelwood, and termolecular Eley-Rideal) of CO oxidation over Ag1/BN are investigated. Due to "CO-Promoted O2 Activation", the termolecular Eley-Rideal (TER) mechanism is the most relevant one for CO oxidation over Ag1/BN and the rate-limiting reaction barrier is only 0.33 eV. More importantly, the first principles molecular dynamics simulations confirm that CO oxidation via the TER mechanism may easily occur at room temperature. Analyses with the inclusion of temperature and entropy effects further indicate that the CO oxidation via the TER mechanism over Ag1/BN is thermodynamically favorable in a broad range of temperatures.

Highlights

Carbon monoxide (CO) oxidation has attracted great interest due to its importance in various industrial and environmental applications,[1] and it has become a benchmark reaction for examining the activity of heterogeneous catalysts.[2]
Analyses with the inclusion of temperature and entropy effects further indicate that the CO oxidation via the termolecular Eley–Rideal (TER) mechanism over Ag1/BN is thermodynamically favorable in a broad range of temperatures
We aim to provide answers for the core questions regarding the design and use of SACs: (i) can single Ag atoms be dispersed and kept on hexagonal boron nitride monolayers (h-BN)? If so, (ii) can the Ag1/BN configuration possess high catalytic activity toward the CO oxidation reaction? (iii) What is the most relevant mechanism for CO oxidation? The first principles molecular dynamics (MD) simulations and temperature/ entropy analyses are performed to appreciate the fundamental aspects and microscopic processes regarding the structural stability and reactivity of SACs, respectively

Summary

Introduction

Carbon monoxide (CO) oxidation has attracted great interest due to its importance in various industrial and environmental applications,[1] and it has become a benchmark reaction for examining the activity of heterogeneous catalysts.[2]. To further increase the catalytic performance and reduce the cost, recent research attention has turned to ‘‘single atom catalysts’’ (SACs)[18,19] by downsizing the catalyst to the atomic scale, which provides a platform for the establishment of new fundamental science as well as the design of excellent catalysts. We use a system with a single Ag atom supported on a hexagonal boron-nitride sheet (Ag1/BN) as the prototype SAC and investigate its structural stability and catalytic activity. We aim to provide answers for the core questions regarding the design and use of SACs: (i) can single Ag atoms be dispersed and kept on h-BN? Our studies elucidate mechanisms of CO oxidation over Ag1/BN and shed light on the principles for the design of more effective catalysts based on the SAC concept

Computational details

Structural stability of single Ag adatoms over h-BN

Contribution of van der Waals correction

Effect of temperature and entropy

Conclusion