Unlocking Optimal Performance of PGM-Free CeCuOx Mixed Oxide Catalysts for CO and C3H6 Emission Conversion

Abstract

A sustainable and cost-effective alternative for environmental applications is the use of PGM-free catalysts, which are crucial for pollutant removal. This research employed the sol-gel method to synthesize stable and effective mesoporous CeCuO_x mixed oxide catalysts to facilitate the oxidation of CO and C₃H₆ emissions at lower temperatures. Additionally, pure CeO₂ and CuO were also synthesized for comparative analysis. Catalytic performance was considerably increased by doping CeO₂ with Cu, whereas pure CuO and CeO₂ showed modest activity. XRD, SEM, BET, XPS, Raman spectroscopy, H₂-TPR, and CO-TPD showed that increasing Ce content produced a consistent pore structure without aggregation. In contrast, higher Cu concentration resulted in bulk CuO production, which led to decreased catalytic performance. In particular, the production of isolated CuO_x species partly covered or clogged pores when the Cu level was above 20 wt%, which reduced the total number of effective sites for O₂ activation. Compared to other mixed and pure oxides, the ideal catalyst, Ce₇Cu₃Ox (T_{90, CO} = 178 °C), showed smaller particle size, higher specific surface area, and a larger lattice oxygen species and oxygen vacancies concentration. Additionally, it showed the best CO and C₃H₆ conversion due to its high Ce³⁺ concentration and interfacial active Cu species ratio. H₂-TPR and CO-TPD analyses demonstrated that Ce-Cu mixed oxides with optimal Ce/Cu ratios, particularly Ce₇Cu₃O_x and Ce₅Cu₅O_x, achieve enhanced reducibility and balanced CO adsorption, which are critical for maximizing catalytic reactivity. The catalytic activity exhibited the following sequence: Ce₇Cu₃O_x > Ce₅Cu₅O_x > Ce₉Cu₁O_x > Ce₃Cu₇O_x > Ce₁Cu₉O_x > CuO > CeO₂. This investigation offers a valuable perspective on the mechanisms of Ce-Cu interaction, which contributes to developing high-performance CeCuOx catalysts that are free of PGMs and operate under realistic reaction conditions.

Graphical abstract