Operando Spectroscopic Study of Reduction and Oxidation Half-Cycles in NH3-SCR over CeO2-Supported WO3

Operando spectroscopies (in situ Ce andW 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 exploitedto elucidate reduction/oxidation half-cycles in the selective catalyticreduction of NO with NH3 (NH3-SCR) overWO(3)-loaded CeO2. The Ce4+ specieswas reduced by NO + NH3 to yield N-2 and Ce3+ species (reduction half-cycle), which was then reoxidizedby O-2 (oxidation half-cycle). The oxidation state of theW(6+) species remained unchanged under redox conditions.IR and theoretical results indicated that the reduction half-cyclestarted with the reaction of W6+-OH and adjacentCe(4+)-O with NO to afford Ce3+ speciesand gaseous HONO, which was converted to NO+ species onthe catalyst. The NO+ species then reacted with NH3 to generate N-2.

Automated summary

In this study, operando spectroscopies were used to investigate the selective catalytic reduction of NO with NH3 over WO(3)-loaded CeO2. The reduction/oxidation half-cycles were elucidated through in situ Ce and W L-3-edge X-ray absorption near-edge structure, UV-vis, and infrared spectroscopies. The Ce4+ species were reduced by NO + NH3 to yield N-2 and Ce3+ species in the reduction half-cycle, which were then reoxidized by O-2 in the oxidation half-cycle. The oxidation state of the W(6+) species remained unchanged under redox conditions. IR and theoretical results suggested that the reduction half-cycle started with the reaction of W6+-OH and adjacent Ce(4+)-O with NO to afford Ce3+ species and gaseous HONO, which was then converted to NO+ species on the catalyst. The NO+ species reacted with NH3 to generate N-2.