Revealing the Intricate Structure of Surface Phases of Methanol on In₂O₃(111)

Research on sustainable energy has intensified to reduce greenhouse gas emissions, especially CO₂. One promising strategy is the catalytic reduction of CO₂ to methanol, and indium oxide (In₂O₃) has emerged as a highly efficient catalyst, with high turnover rates and selectivity. This work investigates methanol, the end product of CO₂ reduction, and its interaction with the In₂O₃(111) surface. Utilizing an ultrahigh vacuum (UHV) environment, this study combines temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), noncontact atomic force microscopy (nc-AFM), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The coverages investigated range from 1 to 12 methanol molecules per unit cell. The results are compared to water adsorption on In₂O₃(111), as the chemical behavior of both molecules is similar in many respects. At low coverage, the adsorption patterns and interactions with the In₂O₃(111) surface mirror those seen with water, including dissociative and molecular adsorption. The first three methanol molecules dissociate at specific sites within the surface unit cell, while molecular adsorption becomes favored for subsequent molecules at temperatures below 300 K. At the highest coverage (before multilayer adsorption) methanol and water exhibit distinct structures due to their differing hydrogen bonding capabilities.