Highly efficient nanosized Mn and Fe codoped ceria-based solid solutions for elemental mercury removal at low flue gas temperatures

Abstract

Ceria (CeO₂) is a well-known material for various industrial applications due to its unique redox properties. Such properties, dominated by structural defects that are primarily oxygen vacancies associated with the Ce³⁺/Ce⁴⁺ redox couple, can be easily modulated and optimized by different approaches. In this paper, nanosized Mn and Fe codoped CeO₂ solid solutions, Ce_0.7−xMn_0.3Fe_xO_2−δ (x = 0.05–0.2), were prepared by a simple coprecipitation method and tested towards elemental mercury (Hg⁰) oxidation and adsorption. The obtained solid solutions were characterized in detail at the structural and electronic level by various techniques, namely, XRD, ICP-OES, BET surface area, TEM, Raman, H₂-TPR, and XPS. The XRD results suggest that the Mn and/or Fe dopant cations are effectively incorporated into the CeO₂ lattice. BET surface area results suggest that the addition of Mn and/or Fe dopants to CeO₂ significantly reduces its crystallite size and thereby improves the surface area. Raman, H₂-TPR, and XPS results reveal that the Mn and/or Fe dopant cations in the ceria lattice increased the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce⁴⁺/Ce³⁺. The Hg⁰ oxidation and adsorption studies indicate that Ce_0.7−xMn_0.3Fe_xO_2−δ solid solutions exhibited the highest activity compared to pure CeO₂. In particular, the Ce_0.5Mn_0.3Fe_0.2O_2−δ (CMF20) solid solution shows an Hg⁰ oxidation efficiency (E_oxi) of 86.5%. It was found that the doping of both Mn and Fe led to lattice distortion and restrained growth of CeO₂, resulting in synergistic increase in oxygen vacancies and catalytic activity.