Performance study on low-temperature hydrolysis of carbonyl sulfide catalyzed by lanthanum-doped rod-shaped ceria catalyst

This study undertook a thorough examination of three different morphologies (rod-shaped, cubic, and spherical) of CeO₂ and La-doped catalysts on CeO₂. The focus was on understanding the impact of alkaline site quantity and intensity on catalytic activity. Additionally, it explored how introducing oxygen vacancies affects H₂O activation and dissociation, which leads to the formation of hydroxyl groups, ultimately boosting COS hydrolysis activity. The deactivation mechanism of the catalyst was also discussed. Initially, the rod-shaped morphology (CeO₂−R) displayed more oxygen vacancies on the (110) crystal plane. This unique characteristic contributed to enhanced catalytic efficiency in COS hydrolysis. When 10% La was doped onto CeO₂−R, it resulted in the formation of a solid solution. This synergistic effect of La with CeO₂ led to the creation of more asymmetric oxygen vacancies on the catalyst surface, which further stimulated H₂O activation and dissociation, thereby advancing COS hydrolysis activity. Several techniques, such as CO₂−TPD and EPR, were employed to investigate the influence of alkaline sites and oxygen vacancies on COS removal. The results suggested that alkaline sites were advantageous for low-temperature COS hydrolysis, whereas oxygen vacancies served as surface defects, promoting the formation of —OH functional groups. The combined effect of oxygen vacancies and alkaline sites facilitated COS and water adsorption, thereby enhancing the catalytic hydrolysis efficiency. Further characterization using XPS revealed variations in the Ce₃+ species content on the catalyst surface during the catalytic reaction, which are closely linked to the generation and consumption of oxygen vacancies. Simultaneously, the O 1s spectra suggested that oxygen vacancies on the catalyst surface played a pivotal role during the reaction. In addition, XPS and S 2p spectra analyses revealed the generation of sulfate salts during the reaction, likely arising from by-products of COS hydrolysis. This development led to pore blockage and active center coverage, resulting in sulfur poisoning of the catalyst. This was identified as a major cause of catalyst deactivation. The study also underscored the importance of an appropriate oxygen content in enhancing the removal efficiency of the catalyst. Excessive oxygen content could lead to catalyst deactivation, highlighting the need for balance. Further investigations through in-situ diffuse reflectance infrared spectroscopy (in situ DRIFTS) experiments provided insights into the surface functional group changes and gas products during the heterogeneous hydrolysis reaction on the 10La–CeO₂ catalyst. The experimental results indicated that HSCO₂ was the main intermediate product, with surface —OH groups and oxygen vacancies actively participating in the hydrolysis reaction. In summary, this study systematically elucidated the performance and mechanisms of CeO₂ catalysts in different morphologies and doping conditions for COS removal. These findings provide valuable information for catalyst design and optimization for low-temperature catalytic COS hydrolysis.