Abstract
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.
Highlights
58 °C, owned the smaller particles size of CeO2 and CuO, and exhibited the higher concentration of Olatt species and oxygen vacancies
The introduction of CeO2 nanorods greatly decreased the energy barrier of Carbon monoxide (CO) oxidation reaction, while the using of flower-like CeO2 microspheres resulted in the higher energy barrier of CO oxidation
Cu/CeO2 catalysts with different morphology and size have been successfully synthesized by hydrothermal and solvothermal methods, and followed by deposition precipitation process. These catalysts were studied for the catalytic oxidation of CO under dry and humid conditions to explore the shape effect on CO oxidation performance
Summary
Received: 1 March 2019 Accepted: 29 July 2019 Published: xx xx xxxx defects of Cu/CeO2 catalysts applied for low-temperature CO oxidation. 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. The structure of CeO2 as support is vitally significant for improving the activity of ceria-based catalysts It is well-known that copper-based solids are attractive because of their application as efficient catalysts in various redox reactions, including the oxidation of CO and volatile organic compounds[28,29], alcohol synthesis[30,31], the water-gas shift reactions and so on[22,32,33]. D. Zhang et al.[40] synthesized a series of Cu-doped CeO2 hollow spheres by a simple hydrothermal method, and discovered that the superior catalytic performance for CO oxidation reaction is ascribed to the porous spherical structure, high redox capability and high oxygen vacancy. The morphology of CeO2 support greatly altered the particles size of CeO2 and CuO, which were considered as one of factors to determine the catalytic performance of Cu/CeO2 catalysts
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