Effect of sulfate species on the performance of Ce-Fe-O_x catalysts in the selective catalytic reduction of NO by NH₃

A series of Ce-Fe-O_x catalysts containing sulfate species was prepared by four different methods including sol-gel (Fe-SG), hydrothermal (Fe-HT), co-precipitation (Fe-10) and solid state grinding synthesis (Fe-SSGS) methods. The Ce-Fe-O_x catalysts were used in the selective catalytic reduction (SCR) of NO_x by NH₃ and the effect of sulfate species on the catalytic performance was investigated. The results indicate that the Fe-HT catalyst prepared by the hydrothermal method exhibits excellent performance in the NH₃-SCR of NO, with a NO conversion of nearly 100% even at 250 °C. The Fe-HT catalyst contains proper amount of sulfate, which can decrease the CeO₂ crystallinity and enhance the catalytic performance in the NH₃-SCR of NO. The Fe-HT catalyst has a high content of surface Ce³⁺ and Fe³⁺ and there is a synergy between the Fe and Ce species, which can improve the redox capacity and greatly increase the quantity of chemisorbed oxygen. In contrast, excessive amount of sulfate species in Fe-SSGS and Fe-SG may reduce the synergy between Fe and Ce and then impair the catalytic performance of Ce-Fe-O_x in NH₃-SCR.