Fe 2 O 3 –CeO 2 @Al 2 O 3 Nanoarrays on Al-Mesh as SO 2 -Tolerant Monolith Catalysts for NO x Reduction by NH 3

Currently, selective catalytic reduction of NO x with NH 3 in the presence of SO 2 is still challenging at low temperatures (<300 °C). In this study, enhanced NO x reduction was achieved over a SO 2 -tolerant Fe-based monolith catalyst, which was originally developed through in situ construction of Al 2 O 3 nanoarrays (na-Al 2 O 3 ) on the monolithic Al-mesh by a steam oxidation method followed by anchoring Fe 2 O 3 and CeO 2 onto the na-Al 2 O 3 @Al-mesh composite by an impregnation method. The optimum catalyst delivered more than 90% NO conversion and N 2 selectivity above 98% within 250–430 °C as well as excellent SO 2 tolerance at 270 °C. The strong interaction between Fe 2 O 3 and CeO 2 enabled favorable electron transfers from Fe 2 O 3 to CeO 2 while generating more oxygen vacancies and active oxygen species, consequently accelerating the redox cycle. The improved reactivity of NH 4 + with nitrates following the Langmuir–Hinshelwood mechanism and active NH 2 species that directly reacted with gaseous NO following the Eley–Rideal mechanism enhanced the NO x reduction efficiency at low temperatures. The preferential sulfation of CeO 2 alleviated the sulfation of Fe 2 O 3 while maintaining the high reactivities of NH 4 + and NH 2 species. Especially, the SCR reaction following the Eley–Rideal mechanism largely improved the SO 2 tolerance because NO does not need to compete with sulfates to adsorb on the catalyst surface as nitrates or nitrites. This work paves a way for the development of high-performance SO 2 -tolerant SCR monolith catalysts.