A deep insight into arsenic adsorption over γ-Al2O3 in the presence of SO2/NO

Abstract Arsenic is easily evaporated during coal combustion, which not only raises serious environmental concerns but also results in the deactivation of catalyst in selective catalytic reduction (SCR) systems. It is a promising method to use sorbents for the capture of arsenic vapors (As 2 O 3 (g)) before As-containing flue gas entering SCR catalyst. However, arsenic has a strong affinity with sulfur in coal and SO 2 in the coal combustion flue gas strongly suppresses As 2 O 3 (g) capture by typical Ca/Fe-based sorbents. This study estimated the selective capture of As 2 O 3 (g) by γ-Al 2 O 3 and the effects of SO 2 and NO on the arsenic adsorption were investigated. The results showed that As 2 O 3 (g) adsorption over γ-Al 2 O 3 was effectively conducted at temperatures ranging from 300 to 400 °C. In the reacted γ-Al 2 O 3 , arsenic was predominantly in the form of As 3+ through reactions with Al-O bonds and positive charged alumina ions. SO 2 was slightly adsorbed on γ-Al 2 O 3 , which had a limited effect on arsenic adsorption. The adsorption of SO 2 on γ-Al 2 O 3 mainly occurred on the sites of hydroxyl groups (Al-OH) and few adsorbed SO 2 was bound with positive charged alumina ions. NO was catalytically oxidized by γ-Al 2 O 3 and released as NO 2 . Nevertheless, NO competed with As 2 O 3 (g) to adhere to positive charged alumina ions and strongly suppressed arsenic adsorption over γ-Al 2 O 3 . Fortunately, in the presence of SO 2 , NO was mostly transformed into intermediate (-SO 3 NO) at the sites of Al-OH on γ-Al 2 O 3 . As a result, the adverse effect of NO on the adsorption of As 2 O 3 (g) was weakened.