Understanding of Low-Temperature CO Oxidation Active Sites on Atomically Dispersed Cu/CeO Synthesized via High-Temperature Synthesis
Yong Wang, Institute for Integrated Catalysis – Pacific Northwest National laboratory
The remarkable redox properties of Cu/CeO2 catalysts have widely attracted the interest of the scientific community in the past two decades. Given its intrinsic low-temperature CO oxidation activity, these materials are attractive candidates to replace expensive PGM-based catalysts to comply with the most recent and stringent emissions abatement regulations, in which colder exhaust gasses must be oxidized as a result of more energy-efficient engines. Understanding the nature of low-temperature CO oxidation active site on Cu/CeO2 is a crucial stage for its implementation in emission-treatment technologies, but it has remained elusive given the lack of scientific consensus derived from unclear structure activity relationships as a result of fundamental studies done on materials with poorly controlled structures. Our group has recently reported a high-temperature method for the synthesis of thermally stable atomically dispersed Pt/CeO2 . It was also shown how materials made with such method had improved redox properties as a result of lattice oxygen activation. In this work, we used the high-temperature synthesis approach to obtain highly active Cu/CeO2 for low-temperature CO oxidation. In addition, we methodologically varied the types of Cu species by controlling the Cu loading. As a result, we were able to obtain atomically dispersed Cu/CeO2 and a mixture of atomically dispersed Cu/CeO2 and CuO2 species. With the use of CO-TPR, the active lattice oxygen was quantified and related to TOF calculations, revealing that active lattice oxygen (Cu-O-Ce) plays a crucial role on the low-temperature CO oxidation. The improved redox properties of Cu/CeO2 catalysts were confirmed by XPS and DRIFTS studies and with the use of XRD, XAS and DFT calculations an understanding of the low-temperature CO oxidation active site is proposed.