Revelation of HCl poisoning and enhancement mechanism on N-modified Al2O3 catalysts for COS and CS2 hydrolysis

Abstract

The presence of HCl in blast furnace gas significantly inhibits hydrolytic activity and catalyst stability. The anti-chlorine capacity and poisoning mechanism of Al2O3 catalysts before and after nitrogen modification was investigated by activity evaluation, characterization analysis and theoretical calculations. In the presence of 0.01 vol% HCl, the COS and CS2 conversions of K0.1Al2O3 catalysts decreased rapidly after 4 h of reaction, which was amended by N doping. The N0.1K0.1Al2O3 catalyst maintained 48.23 % COS conversion and 45.41 % CS2 conversion, respectively, after 16 h reaction. The deteriorated reactivity was mainly associated with the decreased specific surface area, reduced chemisorbed oxygen, disrupted basicity and COS and CS2 adsorption ability. Sulfate and HCl on the surface of the unmodified catalyst mainly destroyed the Al sites and led to catalyst deactivation. N doping reinforced the tendency of toxic molecules to adsorb at the K site (K2SO4 and KCl) and thus protected the Al active site. DFT calculation results demonstrated the inhibition of HCl adsorption at the Al site by N modification, while the trapping of HCl by both K and N sites efficiently protected the Al site from acidification. The reaction pathway calculations certified that N doping increased the energy barrier of the HCl dissociation reaction, which inhibited the acidification and deactivation of Al2O3 to some extent.