Pore surface engineering of Al2O3-supported Ru catalysts with TiO2 for enhanced selective CO methanation

Abstract

Hydrogen-rich gas derived from hydrocarbons contains large amounts of CO2 and CO, with the latter being poisonous for low-temperature polymer exchange membrane fuel cell anodes. Therefore, the efficient removal of CO from reformate gases is crucial while minimizing the methanation of CO2 to reduce unnecessary hydrogen consumption. In this study, Ru-based catalysts, which are ready to be employed in a chemical reactor, are developed to selectively convert CO into CH4 with minimal CO2 methanation using a simulated gas mixture composed of 75 % H2, 24 % CO2, and 1 % CO. The CO adsorption capability of Ru catalysts was enhanced by controlling the surface pores with a TiO2 coating layer. In this process, egg-shell type TiO2/Al2O3 supports were synthesized by wet impregnation method, and then Ru was impregnated on the supports. This modification enabled the Ru/TiO2/Al2O3 to preferentially adsorb CO over CO2. Furthermore, by systematically varying the TiO2 loading, the electronic structure of Ru is modified to induce CO adsorption, resulting in a catalyst with maximum activity for selective CO methanation. The catalyst demonstrates a turnover frequency value of 8.6 × 10−3 s−1 at 190°C, surpassing the performance of previously reported catalysts.