Unraveling the Chlorine-Resistance and catalytic activity of alumina-based catalyst in COS hydrolysis for blast furnace gas purification

Abstract

To improve the activity of COS hydrolysis catalysts in a complex atmosphere is a significant challenge for blast furnace gas purification. Alumina-based hydrolysis catalysts were prepared with four alkali/alkaline earth metals (Na, K, Mg and Ca) respectively by the simple impregnation method to explore the chlorine-resistance mechanism of catalysts. Among four catalysts, Na/Al₂O₃ and K/Al₂O₃ catalysts showed a higher hydrolysis conversion of COS reaching 98% for 12 h in the absence of HCl, due to the higher contents of weak basic sites as active sites for COS adsorption and more migratory oxygen species participating in COS hydrolysis. Especially, K/Al₂O₃ has the highest catalytic activity in that it is easy to adsorb COS and H₂O due to their high absolute adsorption energy. The presence of HCl inhibits the hydrolysis of COS owing to the acidification of active components and competitive adsorption with COS and H₂O. It has been further found that HCl also inhibits the migration of oxygen species and deposition of sulfur species, but HCl still has a stronger inhibitory effect on COS hydrolysis than the deposition of sulfur species. The introduction of alkali metal as sacrificial sites protects the structure of alumina-based catalysts, avoiding the combination of HCl and Al-O to generate Al-Cl. Na/Al₂O₃ has the best Cl-resistance mainly due to the high content of medium basic sites and great bond energy of Na-O with HCl. This research offers valuable guidance for the rational design and preparation of alumina-based catalysts with a good Cl-resistance and for the applications of blast furnace gas purification.