The adsorption and catalytic oxidation of the element mercury over cobalt modified Ce–ZrO2 catalyst

Abstract

Co was used as a modifier for Ce–ZrO₂ to improve the surface physicochemical properties of the catalysts. The obtained catalysts Co_x–Ce–ZrO₂ were investigated for Hg⁰ adsorption and oxidation in the temperature range of 100–350 °C. The results showed that Co modified catalysts had an excellent Hg⁰ removal efficiency. For Co_0.3–Ce–ZrO₂, the Hg⁰ adsorption efficiency was above 81.5% even after a 164.5 h adsorption test and the Hg⁰ oxidation efficiency reached 100% in the temperature range of 100–250 °C. XRD, BET and XPS results suggested that the Co modified catalysts had larger surface areas and more oxygen vacancies. H₂-TPR results showed that Co addition improved the redox performance of the catalyst. These results led to a better Hg⁰ removal efficiency by the Co modified catalysts. Furthermore, XPS results of Co_0.3–Ce–ZrO₂ before and after reaction showed that, during the Hg⁰ oxidation process, surface chemisorbed oxygen was dramatically consumed while some Co³⁺ and Ce⁴⁺ changed to Co²⁺ and Ce³⁺. This suggested that chemisorbed oxygen participated in the Hg⁰ oxidation process. A probable pathway of Hg⁰ oxidation was deduced based on these results. The effects of individual flue gas components (O₂, NO, H₂O, SO₂) on Hg⁰ oxidation efficiency were investigated and the results showed that O₂ and NO improved the Hg⁰ oxidation efficiency whereas H₂O and SO₂ inhibited it.