Catalytic oxidation and adsorption of elemental mercury over nanostructured CeO2–MnOx catalyst

A nanostructured CeO2–MnOx catalyst was synthesized by a coprecipitation method and subjected to different calcination temperatures at 773 and 1073 K to understand the surface structure and the thermal stability. The structural and redox properties were deeply investigated by various techniques, namely, X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP-OES), Brunauer–Emmett–Teller (BET) surface area, transmission electron microscopy (TEM), Raman spectroscopy (RS), hydrogen-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The CeO2–MnOx catalyst calcined at 773 K was tested towards elemental mercury (Hg0) oxidation and the achieved results are compared with the pure CeO2 and MnOx. The XRD and TEM results confirmed the incorporation of Mn ions into the ceria lattice and the formation of a nanostructured solid solution, respectively. The RS and TPR results showed that the CeO2–MnOx catalyst exhibits more oxygen vacancies with superior redox ability over CeO2 and MnOx. XPS analysis indicates that Ce and Mn existed in multiple oxidation states. Compared to pure CeO2 and MnOx, the CeO2–MnOx catalyst exhibited greater Hg0 oxidation efficiency (Eoxi) of 11.7, 33.5, and 89.6% in the presence of HCl, O2, and HCl/O2-mix conditions, respectively. The results clearly indicated that the HCl/O2-mix had a promotional effect on the catalytic Hg0 oxidation. This was most likely due to the presence of surface oxygen species and oxygen vacancies being generated by a synergetic effect between CeO2 and MnOx. In the presence of HCl, the CeO2–MnOx catalyst exhibited good adsorption efficiency (Eads) of 92.4% over pure CeO2 (46.5%) and MnOx (80.6%). It was found that increasing the operating temperature from 423 to 573 K resulted in considerable increase of Eoxi and a decrease in the sorption of Hg0 on the catalyst.