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

The Hg-0 adsorption and oxidation sites on the CuCl2-MF catalyst as well as the role of atomic Cu and Cl in Hg-0 removal were identified by a temperature programmed desorption (TPD) experiment. The reaction mechanism with the participation of O-2 and HCl was investigated. The changes in surface chemistry of fresh, spent and in situ pretreated catalyst with O-2 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. O-2 and HCl significantly affected the state of Cu and Cl on the spent catalyst. The interaction between Hg-0 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 Hg-0, (2) the reoxidation of CuCl for the interaction with O-2 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 Hg-0 and CuCl2 is a cycle when O-2 and HCl are contained in the reaction system. (C) 2015 Elsevier Ltd. All rights reserved.