Catalytic hydrolysis of COS over unsupported Al2O3: New insights into the influence of hydroxyl characteristics on hydrolysis efficiency

Abstract

H2O molecules are challenging to dissociate at low temperatures to produce hydroxyl groups for heterogeneous carbonyl sulfide (COS) hydrolysis. Utilizing the inherent hydroxyl groups on Al2O3 surfaces for catalytic COS hydrolysis is effective; however, the relationship between the hydroxyl nature and hydrolysis efficiency remains unclear. In this study, we investigated the effects of crystal structure, surface morphology, specific surface area, and hydroxyl characteristics of Al2O3 on COS hydrolysis efficiency. Results showed that the content, stability, and activity of hydroxyl groups significantly impacted the efficiency. Catalysts prepared from commercial alumina (Al2O3-C) exhibited superior COS hydrolysis efficiencies under both dry and humid conditions compared to pseudo-boehmite derived Al2O3 (Al2O3-S) and boehmite derived Al2O3 (Al2O3-B) owing to the higher, more stable, and active hydroxyl content in Al2O3-C. Although Al2O3-S contained a sufficient amount of surface hydroxyl, its lower activity reduced the hydrolysis efficiency. The catalytic COS hydrolysis mechanism over hydroxyl-rich Al2O3 was elucidated through various characterization methods, providing new insights into the correlation between Al2O3 surface hydroxyl properties and COS hydrolysis efficiency.