Strong interaction of tetrabutylphosphonium chloride and γ-Al2O3 induces dissociation of H2O and generation of basic hydroxyl groups for promoting the carbonyl sulfide hydrolysis at a low temperature

In this study, we report a simple strategy to enhance the low-temperature catalytic performance of γ-Al 2 O 3 for carbonyl sulfide (COS) hydrolysis by regulating the dissociation of H 2 O. Specifically, tetrabutylphosphonium chloride (TBuPC), an ionic liquid, was introduced onto γ-Al 2 O 3 via ultrasonic impregnation. There was a strong interaction between Cl in TBuPC and Al sites in tetrahedral interstices of γ-Al 2 O 3 , and Al sites in octahedral interstices were acted as main adsorption sites of H 2 O. Additionally, the hydrogen bond Cl···H-O lowered the dissociation energy of H 2 O on Al sites in octahedral interstices of γ-Al 2 O 3 , leading to the generation of abundant basic –OH groups, which served as active sites for COS adsorption and hydrolysis. Consequently, 3TBuPC/γ-Al 2 O 3 achieved 100 % COS conversion at 60 °C, which was 2.05 times higher than that of γ-Al 2 O 3 . The catalytic mechanism of COS hydrolysis over 3TBuPC/γ-Al 2 O 3 involved the following steps: (1) H 2 O was adsorbed on the γ-Al 2 O 3 surface and dissociated, generating H* and basic –OH groups; (2) COS was adsorbed on the –OH sites, forming the intermediate HSCO 2 - ; (3) HSCO 2 - reacted with H* to release CO 2 and H 2 S. This significant enhancement provides a new insight for the design and development of low-temperature hydrolysis catalysts.