How Rh surface breaks CO molecules under ambient pressure.

Utilization of carbon dioxide (CO) molecules leads to increased interest in the sustainable synthesis of methane (CH) or methanol (CHOH). 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 CO dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO. The linear geometry of CO gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO 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.