Fe_2O_3-CeO_2@Al_2O_3 Nanoarrays on Al-Mesh as SO_2-Tolerant Monolith Catalysts for NO_x Reduction by NH_3

摘要

Currently, selective catalytic reduction of NOx with NH3 in the presence of SO2 is still challenging at low temperatures (300 degrees C). In this study, enhanced NOx reduction was achieved over a SO2-tolerant Fe-based monolith catalyst, which was originally developed through in situ construction of Al2O3 nanoarrays (na-Al2O3) on the monolithic Al-mesh by a steam oxidation method followed by anchoring Fe2O3 and CeO2 onto the na-Al2O3@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 degrees C as well as excellent SO2 tolerance at 270 degrees C. The strong interaction between Fe2O3 and CeO2 enabled favorable electron transfers from Fe2O3 to CeO2 while generating more oxygen vacancies and active oxygen species, consequently accelerating the redox cycle. The improved reactivity of NH4+ with nitrates following the Langmuir-Hinshelwood mechanism and active NH2 species that directly reacted with gaseous NO following the Eley-Rideal mechanism enhanced the NOx reduction efficiency at low temperatures. The preferential sulfation of CeO2 alleviated the sulfation of Fe2O3 while maintaining the high reactivities NH4+ and NH2 species. Especially, the SCR reaction following the Eley-Rideal mechanism largely improved the SO2 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 SO2-tolerant SCR monolith catalysts.