Insight into NH3-SCR and H2O/SO2 resistance of Ce modified iron-based catalysts with the presence of arsenic

Abstract

The mechanism of denitrification and arsenic poisoning during the selective catalytic reduction of NO_x with ammonia using a cerium-modified iron-based catalyst was investigated through fixed bed activity tests and catalyst characterization. The results demonstrated that cerium formed a solid solution with Fe, and enriched the surface acid sites of the catalyst. Furthermore, cerium inhibited the arsenic-iron interaction, thereby protecting the active sites of the catalyst. After 6 h of arsenic poisoning, the NO_x conversion of 0.1Ce catalyst decreased by only about 30 % of that of Fe₂O₃ catalyst. The cerium-modified iron-based catalyst exhibited significantly better H₂O resistance than the Fe₂O₃ catalyst at 300 °C, and increased as the temperature rose·H₂O adsorbed onto the Lewis acid sites on the catalyst surface, converting them into Brønsted acid sites, which promoted arsenic adsorption and oxidation on the surface, thereby greatly reducing adsorption activity of the catalyst. In the presence of SO₂ and As₂O₃ in the flue gas, the denitrification efficiency of the catalyst further decreased, though the reduction is less pronounced than in the presence of H₂O and As₂O₃ alone, and shows a negative correlation with SO₂ concentration.