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 (As2O3(g)) before As-containing flue gas entering SCR catalyst. However, arsenic has a strong affinity with sulfur in coal and SO2 in the coal combustion flue gas strongly suppresses As2O3(g) capture by typical Ca/Fe-based sorbents. This study estimated the selective capture of As2O3(g) by γ-Al2O3 and the effects of SO2 and NO on the arsenic adsorption were investigated. The results showed that As2O3(g) adsorption over γ-Al2O3 was effectively conducted at temperatures ranging from 300 to 400 °C. In the reacted γ-Al2O3, arsenic was predominantly in the form of As3+ through reactions with Al-O bonds and positive charged alumina ions. SO2 was slightly adsorbed on γ-Al2O3, which had a limited effect on arsenic adsorption. The adsorption of SO2 on γ-Al2O3 mainly occurred on the sites of hydroxyl groups (Al-OH) and few adsorbed SO2 was bound with positive charged alumina ions. NO was catalytically oxidized by γ-Al2O3 and released as NO2. Nevertheless, NO competed with As2O3(g) to adhere to positive charged alumina ions and strongly suppressed arsenic adsorption over γ-Al2O3. Fortunately, in the presence of SO2, NO was mostly transformed into intermediate (-SO3NO) at the sites of Al-OH on γ-Al2O3. As a result, the adverse effect of NO on the adsorption of As2O3(g) was weakened.