Nanocrystalline CeO_2-δ coated β-MnO₂ nanorods with enhanced oxygen transfer property

In this research, β-MnO₂ nanorods were synthesized by a hydrothermal method, followed by a facile precipitation method to obtain nanocrystalline CeO_2-δ coated β-MnO₂ nanorods. The as-prepared samples were characterized by XRD, HRTEM, FESEM, XPS and in-situ high-temperature XRD. The HRTEM results show that well dispersed CeO_2-δ nanocrystals sized about 5 nm were coated on the surface of β-MnO₂ nanorods. The oxygen storage and transfer property of as-synthesized materials were evaluated using TGA under various atmospheres (air, pure N₂, and 5%H₂/95%Ar). The TGA results indicate that CeO_2-δ modification could favour the reduction of Mn⁴⁺ to Mn³⁺ and/or Mn²⁺ at lower temperature as compared with pure β-MnO₂ nanorods and the physically mixed CeO2-δ-β-MnO2 under low oxygen partial pressure conditions (i.e., pure N₂, 5%H₂/95%Ar). Specifically, CeO_2-δ@β-MnO₂ sample can exhibit 7.5 wt% weight loss between 100 and 400 °C under flowing N₂ and 11.4 wt% weight loss between 100 and 350 °C under flowing 5%H2/95%Ar. During the reduction process under pure N₂ or 5%H₂/95%Ar condition, the oxygen ions in β-MnO₂ nanorods are expected to be released to the surroundings in the form of O₂ or H₂O with the coated CeO_2-δ nanocrystals acting as mediator as inferred from the synergistic effect between the well-interacted CeO_2-δ nanocrystals and β-MnO₂ nanorods.