Role of NO in Hg(0) oxidation over a commercial selective catalytic reduction catalyst V2O5-WO3/TiO2.

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst, V2O5-WO3/TiO2, to investigate mercury oxidation in the presence of NO and O2. Mercury oxidation was improved by NO, and the efficiency was increased by simultaneously adding NO and O2. With NO and O2 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 O2. 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(0) oxidation; 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., NO2) 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 O2.