Polymeric vanadyl species determine the low-temperature activity of V-based catalysts for the SCR of NO x with NH 3

-SCR activity of vanadia-based catalysts, especially under low-temperature conditions. The polymeric vanadia-based SCR mechanism reported here advances the understanding of the working principle of vanadia-based catalysts and paves the way toward the development of low vanadium-loading SCR catalysts with excellent low-temperature activity.