Remarkable chlorine-resistance and catalytic activity of MgAl layered double oxides for COS hydrolysis

Hydrolytic catalysts for carbonyl sulfide (COS) in blast furnace gas (BFG) are confronted with severe challenges arising from sulfate deposition and HCl poisoning. Layered double oxides (LDO) are characterized by their abundant basicity and well-dispersed metal ions, with the potential to be applied in acidic atmospheres. We synthesized a series of MgAl-LDO catalysts by the co-precipitation method. The COS hydrolysis activity exhibits a volcano-type depending on Mg:Al ratio, with 2MgAl-LDO showing the optimal performance. 2MgAl-LDO maintains 100% COS conversion for up to 18 h under HCl-free conditions, moreover its COS hydrolysis capacity reaches 0.52 g/g in the presence of HCl. Comprehensive characterization (BET, XRD, XPS, TG-MS, CO 2 -TPD, in-situ DRIFTS, SSNMR and DFT) reveals the superior activity of 2MgAl-LDO. A larger pore size (23.9 nm) facilitates gaseous product diffusion, while an abundance of weak alkaline center (-OH) promotes hydrolysis activity. The highly active sites are further identified as tetrahedrally coordinated Al-derived Al T -O-Mg site, which favor the dissociation of H 2 O to generate terminal hydroxyl groups (HO-μ 1 ) acting as the active centers for COS hydrolysis. The atmosphere switching experiment demonstrates HCl exerts a dual effect on COS hydrolysis, characterized by short-term promotion and long-term inhibition. By increasing the surface H + concentration on the catalyst, HCl facilitates the transformation of the HSCO 2 − intermediate and suppresses the deposition of SO 3 2− /SO 4 2− species. However, HCl simultaneously damages the metal sites and -OH groups, ultimately leading to catalyst deactivation. This work provides valuable guidance for the rational design of sulfate-tolerant and HCl-resistant catalysts for BFG purification applications.