Study on Reactivity of HgO over Activated Carbon with HCl and SO₂ in the Presence of Moisture by Temperature-Programmed Decomposition Desorption Mass Spectrometry

Reactivities of mercury compounds over mercury sorbents with HCl and SO₂ are very important to the design of a solid sorbent for mercury vapor removal from coal-derived flue gases. However, presently available data on the reactivity of mercury oxide over mercury sorbent is insufficient. This study investigated the reactivity of mercury oxide with HCl and SO₂ using a temperature-programmed decomposition and desorption technique and a mass spectrometer (TPDD-mass) method. Mercury desorption from HgO over activated carbon (HgO/AC) was observed at the same temperature range as from HgO/SiO₂, but the mercury desorption peak from the HgO/AC was observed at a higher temperature than from the HgO/SiO₂, indicating that some of the HgO was stabilized by the AC surface. When the HgO/AC was pretreated with HCl-H₂O, the formation of HgCl₂ was suggested by the mass spectra of m/z = 272 and 270. The mercury desorption temperatures in the TPDD spectra were lower than those of nonpretreated samples. On the basis of the shape of the peak, it was conjectured that the mercury evolved from a single surface complex. The main mercury desorption peak was around 240 °C when HgO/AC was pretreated with SO₂-H₂O and occurred at the lowest temperature of the three pretreatments. However, multiple peaks, indicating the formation of multicomplexes, were observed during the pretreatment. A mercury desorption peak (HgO) was observed at the intermediate position between the other two samples pretreated with SO₂ and HCl. The peak shape revealed that the mercury evolved from a single surface complex. It was also suggested that HCl suppressed the sulfuration of HgO by SO₂ during the pretreatment.