<i>Operando</i> Spectroscopic Study of Reduction and Oxidation Half-Cycles in NH<sub>3</sub>–SCR over CeO<sub>2</sub>-Supported WO<sub>3</sub>
Hiroe Kubota, Yuan Jing, Wan Li, Jiahuan Tong, Ningqiang Zhang, Shinya Mine, Takashi Toyao, Ryo Toyoshima, Hiroshi Kondoh, Davide Ferri, Ken‐ichi Shimizu
Abstract
Operando spectroscopies ( in situ Ce and W L 3 -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 NH 3 (NH 3 –SCR) over WO 3 -loaded CeO 2 . The Ce 4+ species was reduced by NO + NH 3 to yield N 2 and Ce 3+ species (reduction half-cycle), which was then reoxidized by O 2 (oxidation half-cycle). The oxidation state of the W 6+ species remained unchanged under redox conditions. IR and theoretical results indicated that the reduction half-cycle started with the reaction of W 6+ –OH and adjacent Ce 4+ –O with NO to afford Ce 3+ species and gaseous HONO, which was converted to NO + species on the catalyst. The NO + species then reacted with NH 3 to generate N 2 .