Morphology effects on surface chemical properties and lattice defects of Cu/CeO2 catalysts applied for low-temperature CO oxidation

Here, we synthesized a series of Cu/CeO₂ catalysts with different morphology and size, including Cu/CeO₂ nanospheres (Cu/CeO₂-S), Cu/CeO₂ nanoparticles (Cu/CeO₂-P), Cu/CeO₂ nanorods (Cu/CeO₂-R) and flower-like Cu/CeO₂ microspheres (Cu/CeO₂-F) to systematically explore the structure-activity relationship in CO oxidation. Crucially, the effect of morphology, crystal size, Ce⁴⁺/Ce³⁺ species, oxygen vacancies derived from the removal of lattice oxygen (Olatt) species in CeO₂ and lattice defect sites on CO activity was revealed through various characterizations. It was clearly discovered that the activity of these catalysts was as follows: Cu/CeO₂-R > Cu/CeO₂-P > Cu/CeO₂-S > Cu/CeO₂-F, and the Cu/CeO₂-R catalyst preferentially showed the best catalytic performance with a 90% conversion of CO even at 58 °C, owned the smaller particles size of CeO₂ and CuO, and exhibited the higher concentration of Olatt species and oxygen vacancies. Besides, it is also verified that the Cu/CeO₂-F sample exhibited the larger CeO₂ crystal size (17.14 nm), which led to the lower Cu dispersion and CO conversion, even at 121 °C (T₉₀). Most importantly, we discovered that the amount of surface lattice defect sites was positively related to the reaction rate of CO. Simultaneously, DFT calculation also demonstrated that the introduced oxygen vacancies in CeO₂ could accelerate the oxidation of CO by the alteration of CO adsorption energy. Therefore, the morphology, the crystal size, the content of oxygen vacancies, as well as lattice defects of Cu/CeO₂ catalyst might work together for CO oxidation reaction.