Selective Hydrogenation of CO₂ From Direct Air Capture to CO Over Na-Promoted Pt Dual-Functional Material

CO₂ capture and reduction (CCR) to CO using dual-functional materials (DFMs) has recently attracted significant attention as a promising strategy for carbon capture and utilization. However, most of the DFMs for CO production reported to date require high-temperature (> 500 °C) and O₂-free conditions. Herein, we used spectroscopic characterization under operating conditions for a detailed investigation of the Pt–Na/Al₂O₃ DFM reported in our previous work that can capture CO₂ and produce CO by selective hydrogenation at moderate reaction temperatures (350 °C) in the presence of O₂. In situ X-ray absorption spectroscopy measurements revealed that the Pt nanoparticles of Pt–Na/Al₂O₃ were more oxidized and electron-deficient than those of Pt/Al₂O₃, even during the reduction step. In situ IR measurements confirmed that the CO and hydrogen species on Pt–Na/Al₂O₃ desorbed at lower temperatures than those on Pt/Al₂O₃. In addition, modulation excitation infrared spectroscopy (ME–IR) revealed the formation of Pt–H and HCOO⁻ intermediates. The Pt–Na/Al₂O₃ material was used for the first time in a system integrating membrane-based direct air capture (m–DAC) and a CCR system for CO production and showed excellent performance. CO selectivity of 93% and CO production concentrations of 1000–2500 ppm were achieved under continuous operation, demonstrating its practical applicability.