Doping Pd2+ into NinCeOx nanofibers promotes low-temperature CO2 methanation

Abstract

CO₂ methanation at low temperatures is still a challenge. Herein, Ni_nCeO_x (n = 1–3) and Ni_2.5Pd_0.1CeO_x nanofibers by electrospinning is reported. The main advantage of this method is to obtain the highly dispersed precursor of palladium, nickel, and cerium, overcoming the difficulty of uniform mixing in conventional preparation methods. The Ni_2.5Pd_0.1CeO_x nanofiber catalyst exhibited outstanding catalytic performance at low temperatures (CO₂ conversion rate = 90.4 %, CH₄ selectivity = 99.6 % at 230 °C) along with exceptional stability over 300 h. EPR, Raman, and O 1s XPS confirmed that Pd²⁺ doping increased oxygen vacancy concentration. In-situ infrared spectroscopy indicated that CO₂ methanation on Ni_2.5CeO_x and Ni_2.5Pd_0.1CeO_x catalysts followed the formate pathways. Pd²⁺ doping increased the number of surface oxygen vacancies and hydroxyl groups, thus increasing the amount of bicarbonates and formates. DFT calculations suggested that Pd²⁺ doping increased CO₂ adsorption energy, and confirmed surface hydroxyl groups and bicarbonate being beneficial for CO₂ methanation, consequently enhancing the activity of Ni_2.5Pd_0.1CeO_x catalyst especially at low temperatures.