The performance and mechanism of transition metal oxide (Fe, Cu, Mn, Ce) on selective catalytic reduction of NO over ZSM-5.

Abstract

Different transition metals (Fe, Cu, Mn, Ce) were used to prepare and characterise catalysts on ZSM-5 via impregnation, for the selective reduction of NO with NH₃. The Fe/ZSM-5 catalyst exhibited excellent NH₃-SCR activity in the 350-450°C temperature range, with a 96.91% NO conversion rate at 431°C. Moreover, the Ce/ZSM-5 and Cu/ZSM-5 catalysts showed superior catalytic activity at low temperatures (88.33% at 250°C and 91.82% at 289°C), while the Mn-modified catalysts exhibited a poor denitrification performance. The results also revealed that metal oxides improved metal ion dispersion, and the Fe and Cu active components were well distributed on the surface of the carrier. Moreover, Lewis acid sites predominately occurred in the active components of the Fe and Cu species, which increases the adsorption capacity. Among the four different metal-supported catalysts, Cu-ZSM-5 had the smallest activation energy. Highly dispersed metal ion active nanoparticles, improved redox properties, and rich acid centres are conducive to the reaction. The In-situ DRIFTs study found that Lewis acid sites play an important role in the denitrification reaction. The apparent reaction activation energy of Cu-ZSM-5 catalyst in four different metal-supported catalysts is the smallest, with an activation energy of 35.1 kJ mol^-1.