Experimental and theoretical research on pore-modified and K-doped Al2O3 catalysts for COS hydrolysis: The role of oxygen vacancies and basicity

Abstract

The high activation temperature and poor stability of COS hydrolysis catalysts greatly hinder its application in the field of blast furnace gas desulfurization. Various organic additives were applied to modulate the pore structure of the catalyst. Combined with the loading of K, the catalytic performance, H2S selectivity and enhanced mechanism of the modified catalysts were deeply explored. The preferred catalyst exhibited an improved low-temperature activity of 97.2 % and H2S selectivity of 91 % at 75 ℃. The COS conversion of the preferred catalyst remained above 95 % after 50 h reaction. The characterization results revealed that the addition of pore modifiers and basic components resulted in a wider pore size distribution and increased specific surface area. More oxygen vacancies and enhanced surface alkalinity were also certified to contribute to the catalysis properties. In-situ DRIFTS results exhibited that the COS adsorption ability was significantly strengthened due to enhanced alkalinity, while more intermediate active species such as HCO3– and HSCO2- were produced. DFT calculation results indicates that the modified catalyst displays larger adsorption energy of reaction gas molecules·H2O molecular promotes the adsorption of COS and H2S, while H2S inhibits the adsorption of COS. The presence of oxygen vacancies promoted the adsorption of COS and weakened the competitive adsorption of COS and H2S. The adsorbed COS reacts with OH– or H species to form the key intermediate HSCO2-, which is further hydrogenated and decomposed into H2S and CO2. The lower energy barrier and shorter reaction steps for the formation of HSCO2- species are the key incentives for the improved activity of the K-modified catalyst.