Effect of La on the structure, selectivity and stability of La/Co 3 O 4 catalysts in preferential oxidation of carbon monoxide in hydrogen-rich streams

<title>Abstract</title> <p> The Co ₃ O ₄ -based catalyst was prepared by precipitation method, followed by lanthanum incorporation through incipient wetness impregnation. All catalysts were evaluated in the preferential oxidation (PROX) of carbon monoxide in hydrogen-rich streams. Catalysts characterised was performed using XRD, TEM, SEM, FTIR, TGA, TPR and XPS. The XRD and FTIR results confirmed the formation of the spinel CO ₃ O ₄ phase. The TPR measurements confirmed the formation of La-O-Co linkage, evidencing strong electronic and structural interaction between La species and Co ₃ O ₄ lattice. This was further confirmed by XPS, which showed an increased concentration of oxygen vacancies and a concomitant decrease in surface hydroxyl groups. This change is associated with a reduction in the fraction of Co ³⁺ relative to Co ²⁺ upon the incorporation of La species to Co ₃ O ₄ . As a result, an improvement in PROX performance was observed for the 1wt.% La/Co ₃ O ₄ catalyst, which exhibited optimum activity at relatively lower temperatures (~ 60 to 120 ^o C). A slight decrease in CO conversion with time on stream was observed for 1wt.% La/Co ₃ O ₄ in the presence of moisture, attributable to La doping, which suppresses OH-vacancy-assisted dissociative adsorption of H ₂ O. Furthermore, the introduction of CO ₂ into the feed resulted in an approximately 30% decrease in catalytic activity with time on stream. Overall, La doped Co ₃ O ₄ appears as a promising catalyst for low temperature (~ 80–120 ^o C) CO reduction in hydrogen rich streams, aligning with requirements for efficient proton exchange membrane fuel cells. </p>