Selecting Reaction Pathways of CO2 Hydrogenation on Ni(111) by Kinetic Hindrance Associated with the Initial Surface Conditions in the Treatment of H2/CO2 Mixed Gas, Studied by Ambient-Pressure X‑ray Photoelectron Spectroscopy.

Two types of surface reaction intermediates were observed in the presence of a H2/CO2 mixed gas on Ni(111), depending on the dosage order of the gases. The observations were carried out by in situ measurements with ambient-pressure X-ray photoelectron spectroscopy. When the CO2 gas was introduced at 300 K prior to the H2 gas, CO2 dissociation occurred. With the opposite order of gas dosage at the same temperature, carboxyl (COOH) formation was observed on the surface. The different reaction pathways originate from initial surface conditions due to the interaction between the first gas and Ni(111). In both cases, the reaction is dominated by COOH formation above 370-420 K, depending on the gas pressure, and is associated with graphitization above 470 K. The different reaction pathways followed according to the dosage order of the gases likely explain the various intermediates observed in previous studies. These results pave a new way to develop CO2 hydrogenation catalyst systems with lower energy consumption.