Synergy of vanadia and ceria in the reaction mechanism of low-temperature selective catalytic reduction of NOx by NH3

Abstract

Elucidation of redox mechanism is vital to develop highly active catalysts for selective catalytic reduction (SCR) of NOx. Here, we apply an integrated experimental and theoretical approach to investigate low-temperature SCR (LT-SCR) mechanism over VOx/CeO2, a model system containing industrially-relevant vanadia active-species and an eye-catching redox support, i.e. ceria, frequently documented in SCR studies. We show that NO oxidative activation to a gaseous nitrite-precursor intermediate, which was trapped by BaO/Al2O3 and further spectroscopically and computationally validated, serves as a key step in LT-SCR. This scheme involves paired contributions from vanadia and ceria, in which vanadium stabilizes at +5 while Ce3+/Ce4+ varies in the redox cascade, and coupling of V5+−OH and proximal Ce4+−O reduces the NO oxidative activation barrier. These findings progress the understanding of LT-SCR mechanism and deliver a specific perspective on the synergy of surface active-sites and supports, which are essential for the design of further improved SCR catalysts.