Elucidation of Ce/Zr Ratio Effects on the Physical Properties and Catalytic Performance of CuOx/CeyZr1-YO2 Catalysts

CeO₂ is widely used as a catalyst support because of its oxygen storage capacity (OSC) and Ce⁴⁺ and Ce³⁺ redox cycle, which help avoid catalyst deactivation by coke formation and improve catalytic activity. However, bulk CeO₂ has shown some limitations, such as low thermal stability, low number of defect sites on its surface, and deactivation of the redox cycle at high temperatures. It has been reported that zirconium (Zr) incorporation in the cerium (Ce) lattice can increase the number of oxygen vacancies, improve catalytic activity and thermal stability. Using a fixed surface density (SD) of copper (# of Cu atoms/nm²) as a surface species, the role of the support (Ce_yZr_1-yO₂ (y = 1.0, 0.9, 0.6, 0.5, and 0.0)) and defect site effects for CO oxidation reaction were investigated. The thermal stability of CuO_x/Ce_yZr_1-yO₂ catalysts at 700 °C and 900 °C calcination temperature as well as the reduction of the surface species was also conducted in order to better understand the role of CuO_x and calcination temperature. The spectroscopic (e.g., Raman, XRD) and microscopic (e.g., SEM-EDX, TEM) characterization techniques were applied to evaluate the defect sites, crystallite size, lattice parameters, and chemical composition of catalysts. CO oxidation with varied CO:O₂ ratios (1:5, 1:1, and 1:0.5 (stoichiometric)) was used as a model reaction to describe the relationship between the structure and catalytic performance of each catalyst. Based on the characterization results of Ce_yZr_1-yO₂ materials, the addition of Zr causes physical and chemical changes to the overall material. The inclusion of Zr into the structure of CeO₂ decreased the overall lattice parameter of the catalyst and increased the number of defect sites, while CuO_x/Ce_yZr_1-yO₂ displayed lower catalytic ability compared to a CuO_x/CeO₂ catalyst. Based on collected Visible and UV Raman spectroscopy data there is a reduction in oxygen vacancies with higher calcination temperature. The results showed a significant change in activity and structural change with varied calcination temperature. It was concluded that defect sites of support material were not directly linked to the catalytic performance over the tested CuO_x/CeO₂ and CuO_x/Ce_yZr_1-yO₂ catalysts.