Effects of doping Mn, Cu and Fe oxides on polyhedron CeO2 catalyst during NH3-SCR reaction

Abstract

BackgroundCeria (CeO2) was considered as one of the most promising catalysts due to its oxygen storage capacity and redox property. However, the low activity of CeO2 catalyst in SCR reaction limited its further application on industrial processes. MethodsTransition metal (Mn, Cu and Fe) oxides were impregnated on nanopolyhedron CeO2 (CeO2-NP) catalysts to investigate the SCR performance. Significant findingsThe Mn-CeO2-NP catalyst displayed the highest NOx conversion (ca. 70% conversion at 300 °C), followed by the Cu-CeO2-NP catalyst (ca. 65% conversion at 300 °C) and then the Fe-CeO2-NP catalyst (ca. 45% conversion at 300 °C). The results of H2-TPR showed that Mn-CeO2-NP and Cu-CeO2-NP catalysts were more efficient in reducing hydrogen at lower temperature than that of Fe-CeO2-NP catalysts. Based on XPS measurements, it was determined that the Oα/(Oα+Oβ) ratio was Mn-CeO2-NP (ca. 65%)> Fe-CeO2-NP (ca. 59%)> Cu-CeO2-NP (ca. 55%) catalyst. It was also shown by Raman spectroscopy that the Mn-CeO2-NP catalyst had a higher concentration of oxygen vacancies than that of the Cu-CeO2-NP and Fe-CeO2-NP catalysts. Meanwhile, more Brønsted acid sites, Lewis acid sites, nitrate and nitrites species were found in the Mn-CeO2-NP catalyst as seen by in situ DRIFT spectra.