Selective Co2 Hydrogenation for Targeted High-Value Products Over Pt/Cd-Tio2

Abstract

This work presents the synthesis of Cd2+ modified Pt-TiO2 (Pt/Cd-TiO2) catalysts via using an excess-solution impregnation method for CO2 hydrogenation catalysis. 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 °C over Pt/Cd-TiO2, which is 25 °C lower than Pt/TiO2 catalyst (250 °C). 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 CO(ads) into CO in the gas phase and inhibits the hydrogenation of CO(ads) 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 which may be caused by the similar atomic radius and electronic orbit of Pt and Cd elements. This study sheds light on the enhanced CO evolution over Pt/Cd-TiO2 in CO2 hydrogenation and provides guidance for catalyst design.

Keywords: CO2 hydrogenation, CO selectivity, Pt/Cd-TiO2 catalyst, CO binding