Removal of elemental mercury from flue gas by recyclable CuCl2 modified magnetospheres catalyst from fly ash. Part 2. Identification of involved reaction mechanism

Abstract

The Hg0 adsorption and oxidation sites on the CuCl2-MF catalyst as well as the role of atomic Cu and Cl in Hg0 removal were identified by a temperature programmed desorption (TPD) experiment. The reaction mechanism with the participation of O2 and HCl was investigated. The changes in surface chemistry of fresh, spent and in situ pretreated catalyst with O2 and/or HCl were investigated by EPR and XPS to better understand the intermediate reaction products and steps. The results suggested that different mercury adsorption sites are existed on the catalyst: Cl adsorption sites and Cu adsorption sites. The binding energy of mercury on the Cu adsorption sites is higher than that on the Cl adsorption sites. O2 and HCl significantly affected the state of Cu and Cl on the spent catalyst. The interaction between Hg0 and CuCl2 with the participation of O2 and/or HCl follows three steps mechanism: (1) the reduction of CuCl2 to CuCl for the interaction with Hg0, (2) the reoxidation of CuCl for the interaction with O2 forming an intermediate copper oxygen chloride species, (3) the rechlorination of oxychloride species resulting in the restoration of CuCl2. This demonstrated that the interaction between Hg0 and CuCl2 is a cycle when O2 and HCl are contained in the reaction system.