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Abstract Title: The Stability of Dual Cooridnation for Mercury Oxide Species over Selective Catalytic Reduction Catalysts
Presenter Name: Hongxiao Zu
Company/Institution: Central South University
Session: Mercury Treatment / Abatement
Co-Authors: Hongxiao Zu

Abstract Information :

Selective catalytic reduction (SCR) facilitates the capture of mercury by wet flue gas desulfurization (WFGD) through oxidizing Hg0 to Hg2+, which is generally regarded as an economic technology. Usually, the complexity of coal-fired flue gas impedes the Hg0 oxidation efficiency of SCR catalysts, which ascribe to the interactions among surface active sites, elemental mercury and various flue gas components. As the fundamental for exploring the influences of complicated flue gas components on Hg0 oxidation, the immobilization states of Hg0 over surface active sites should be essentially investigated. Based on the irregularities in the distribution of surface active sites, surface Hg species probably only partially exhibit the structural features of oxidation product, i.e., mercury oxide (HgO). Thus, through extracting from the infinite O-Hg-O chain in HgO crystal, three basic units, i.e. HgO, Hg2O and HgO2 molecules, were selected to construct surface HgO species over ceria surface for studying Hg0 binding characteristics over typical SCR catalysts. Density functional theory (DFT) calculations indicated that Hg atom tends to simultaneously coordinate with two oxygen atoms to form O-Hg-O structure over ceria surface. Instead, the Hg atom with one oxygen coordination exhibited apparent electron delocalization, implying the instability of O-Hg structure. In addition, lattice oxygen unexpectedly played an important role in the formation of O-Hg-O structure. To verify the feasibility and rationality of the above-established model, the frequent Hg2+ reduction in typical SCR atmosphere was explored through introducing the violent proton transfer. The completely reduction of Hg2+ could be achieved by breaking either Hg-O bonds in O-Hg-O structure after protons attacking, which further demonstrated the instability of the Hg-O structure. Therefore, through properly considering the formation and conversion of O-Hg-O structure over SCR catalysts, the impacts of various flue gas components on Hg0 oxidation could be more reasonably speculated.

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