Abstract: The adsorption/desorption of the key intermediate at the molecular level in CO₂ hydrogenation deserves significant attention since the intermediate stability can greatly affect the products selectivity. Herein, the Pt/Cd-TiO₂ catalysts was reported to improve CH₄ products selectivity in CO₂ hydrogenation. The Pt/Cd-TiO₂ catalyst is thoroughly characterized through XRD, H₂-TPR, Raman, ESR, TEM, XPS, CO₂-TPD, and N₂ sorption experiments. With the introduction of Cd²⁺, CO selectivity increases to 98.1% and CH₄ selectivity decreases to 1.9% over Pt/Cd-TiO₂ compared to Pt/TiO2 (87.5% for CO and 12.5% for CH₄) during CO₂ hydrogenation. Additionally, CO was produced at 225 ℃ over Pt/Cd-TiO₂, which is 25 ℃ lower than Pt/TiO₂ catalyst (250 ℃). In situ FTIR and XPS measurements reveal that the Cd²⁺ could reduce the electron density of Pt nanoparticles (NPs), and the reduced electron density of Pt NPs will contribute to the desorption of adsorbed COads into CO in the gas phase and inhibits the hydrogenation of COads to produce CH₄. During CO methanation contrast experiments, CH₄ evolution decreases by approximately 6.6 times with the introduction of Cd²⁺, indicating that Cd²⁺ hinders the reaction of CO with H to produce CH₄, in accordance with the increased CO selectivity in CO2 hydrogenation over Pt/Cd-TiO2. The CO selectivity were all improved over several cations (Cd²⁺, Mn²⁺, Ba²⁺, K⁺ and Na⁺) promoted Pt/TiO₂, and Pt/Cd-TiO₂ exhibits the highest CO selectivity. This study sheds light on the enhanced CO evolution over Pt/Cd-TiO₂ in CO₂ hydrogenation and provides guidance for catalyst design.

Key words: CO₂ hydrogenation, Pt/Cd-TiO₂ catalyst, electron density, CO selectivity; CO binding