Advances in rational design of catalysts for efficient Hg0 removal

Abstract

This paper reviews the current methods on the rational design of transition metal-based, SCR-based, precious metal-based and fly ash-based catalysts. Catalysts generally contains three components: active sites, promoters, and supports. The construction of active sites for adsorption, oxidation, and desorption of mercury-related species is important. Selection of promoters needs to enhance the functions of active sites or protect active sites from poisoning. Selection of supports should consider the well dispersion of active sites as well as diffusion of reactive gases in pores. The adsorption sites for Hg0 include high valance cations as well as precious metals. Oxidation sites for Hg0 include oxygen vacancy, lattice oxygen, surface active oxygen, halogen species (Cl, Br, and F), and elemental sulfur. Desorption sites normally contain metal cations with weak bonding strength of Hg0. CuO, Fe2O3, and MoO3 have higher reactivity with SO2, and incorporation of these metal oxides protects the active sites from sulfur poisoning. In the selection of supports, SiO2, zeolite, MOFs, and carbon-based materials have large surface area for dispersion of active sites and dominant mesopores. A hierarchical pore structure with reasonable proportions of micropores and macropores is appropriate for Hg0 removal. The design of catalysts considering the existence of gases such as NO, H2S, CO, H2, and SO2 is then discussed and summarized. Overall, this work helps with the development and synthesis of novel and efficient catalysts for Hg0 removal.