Synergistic effect of HC1 and NO in elemental mercury catalytic oxidation over La_2O_3-TiO_2 catalyst

摘要

Elemental mercury (Hg-0) oxidation over a low-temperature La2O3-TiO2 (LaTi) catalyst through a fixed-bed reactor system is reported here. Despite the presence of oxygen (O-2), Hg-0 was not effectively oxidized by either hydrogen chloride (HCl) or nitrogen oxide (NO). However, Hg-0 oxidation over the LaTi catalyst was greatly improved when both HCl and NO were present in the simulated flue gas. Several methods, including X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and temperature-programmed decomposition (TPD), were used to study the inherent mechanisms involved in the Hg-0 oxidation by HCl and NO. The results indicated that the combined presence of HCl and NO exhibited great synergy for Hg-0 catalytic oxidation over the LaTi catalyst. The reaction mechanism is proposed as follows: 1) NO was adsorbed and oxidized on the catalyst surface, forming NO2; 2) the reactive NO2 then oxidized gas phase Hg-0 to mostly HgO, and; 3) HgO reacted with gas phase HCl to produce HgCl2, which escaped from the catalyst's surface. Differing from previously proposed mechanisms, La2O3 was first studied as an active substance in Hg-0 oxidation. These findings are beneficial for those seeking economical and efficient Hg-0 oxidation catalysts for coal-fired power plants.