Operando spectroscopies (in situ Ce and W L₃-edge X-ray absorption near-edge structure, ultraviolet-visible (UV-vis), and infrared (IR) spectroscopies, combined with online analysis of gas-phase products) were exploited to elucidate reduction/oxidation half-cycles in the selective catalytic reduction of NO with NH₃ (NH₃-SCR) over WO₃-loaded CeO₂. The Ce⁴⁺ species was reduced by NO + NH₃ to yield N₂ and Ce³⁺ species (reduction half-cycle), which was then reoxidized by O₂ (oxidation half-cycle). The oxidation state of the W⁶⁺ species remained unchanged under redox conditions. IR and theoretical results indicated that the reduction half-cycle started with the reaction of W⁶⁺-OH and adjacent Ce⁴⁺-O with NO to afford Ce³⁺ species and gaseous HONO, which was converted to NO⁺ species on the catalyst. The NO⁺ species then reacted with NH₃ to generate N₂