Role of NO in Hg~0 oxidation over a commercial selective catalytic reduction catalyst V_2O_5–WO_3/TiO_2

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst,V_2O_5–WO_3/TiO_2,to investigate mercury oxidation in the presence of NO and O_2.Mercury oxidation was improved by NO,and the efficiency was increased by simultaneously adding NO and O_2.With NO and O_2 pretreatment at 350°C,the catalyst exhibited higher catalytic activity for Hg~0 oxidation,whereas NO pretreatment did not exert a noticeable effect.Decreasing the reaction temperature boosted the performance of the catalyst treated with NO and O_2.Although NO promoted Hg~0 oxidation at the very beginning,excessive NO counteracted this effect.The results show that NO plays different roles in Hg~0oxidation; NO in the gaseous phase may directly react with the adsorbed Hg~0,but excessive NO hinders Hg~0 adsorption.The adsorbed NO was converted into active nitrogen species(e.g.,NO_2) with oxygen,which facilitated the adsorption and oxidation of Hg~0.Hg~0 was oxidized by NO mainly by the Eley–Rideal mechanism.The Hg~0 temperature-programmed desorption experiment showed that weakly adsorbed mercury species were converted to strongly bound ones in the presence of NO and O_2.