Adsorption of CO2 on Terrace, Step, and Defect Sites on Pt Surfaces: A Combined TPD, XPS, and DFT Study

The interactions of CO2 with terrace, step, and defect or kink sites on Pt surfaces were investigated using temperature-programmed desorption, X-ray photoelectron spectroscopy, and density functional theory calculations. Desorption peaks of CO2 on Pt(997) were observed at similar to 79, 88-89, similar to 92, and similar to 103 K and were respectively assigned to desorption of CO2 from multilayer CO2 (amorphous CO2), CO2 from terrace, CO2 from step, and CO2 from defect sites. The defect sites, step sites, and terrace sites were saturated in that order before multilayer adsorption occurred. The adsorption energies of CO2 on the terrace, step, and defect sites were estimated to be around -0.23, -0.28, and -0.34 eV, respectively. The experimentally measured adsorption energies of CO2 on Pt were successfully reproduced using the optB86b-vdW, rev-vdW-DF2, and PBE-D2 functionals, and the actual adsorption energies were found to be between those calculated with rev-vdW-DF2 and optB86b-vdW. Additionally, it was found that CO2 adsorption is energetically more stable at higher CO2 coverage than at lower coverage because of CO2-CO2 lateral attractive interactions.