How Rh surface breaks CO2 molecules under ambient pressure

Jeongjin Kim,Kohei Ueda,Jeong Young Park,Hiroshi Kondoh,Kazuhiko Mase,Hyun You Kim,Bongjin Simon Mun,Won Hui Doh,Hyunwoo Ha

doi:10.1038/s41467-020-19398-1

Abstract

Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO2. The linear geometry of CO2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O‒CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.

Highlights

Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH)
Under the CO2 environment, as illustrated in Fig. 1b, linear (l)-CO2(g) molecules randomly collide with surface Rh atoms with kinetic energy (KE) at a given temperature in statistical velocity distribution; such fundamental molecular motions are correlated to a simplified function of chemical potential energy in the established ideal solution at equilibrium
We have revealed a chemical bond cleavage of *O−CO at CO2−Rh(111) interface in reaction environments using NAPSTM and near-ambient pressures (NAP)-X-ray photoelectron spectroscopy (XPS) techniques

Summary

Introduction

Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH). The similar feedstock of H2 and CO2 over silicon[12] or aluminum[13] oxide-supported rhodium (Rh) catalyst selectively yields a major product of methane via the conversion of CO2 to CO at an early step in the CO2RR process[14] In this way, various derivatives of the reactant CO2 molecules could affect multiple steps of transition states and thermodynamic equilibrium potentials, as predicted by theoretical calculations on the tailored surfaces[15], previous studies have assumed the adsorbate CO2 interactions with insufficient knowledge of underlying molecular behavior in operation conditions. Density functional theory (DFT) calculations elucidate a possible reaction route for the observed CO2 dissociation process with an activation energy barrier (Ea) of 0.58 eV on account of the nonuniform distribution of charge transfers between the bent (b)CO2 molecule and Rh surface atoms

Methods

Results

Conclusion