Volume 31: Clean Energy Technologies towards Carbon Neutrality

Mechanistic assessments of NO activation on WO3-promoted CeO2 catalysts and its consequences for low-temperature NH3-SCR Wenshuo Hu1 #, Yu Zhang1 #, Xiaoxiang Wang2, Weihong Wu1, Hao Song1, Shaojun Liu1*, Xiang Gao1

Abstract

Ceria has absorbed extensive interests in mediating low-temperature (LT) selective catalytic reduction (SCR) of NOx due to its abundance of surface oxygen species and consequential salient redox property. The mechanistic interpretations of how such redox property contributes to its LT-SCR activity, however, still remain debated. Here, we use a model WO3-promoted CeO2 catalyst (WO3/CeO2), known as preeminent in LT-SCR reactions, and combine kinetic, characteristic and in situ spectroscopic experiments with theoretical treatments to reveal the mechanistic connections between NO oxidative activation and LT-SCR turnovers. We show that NO oxidation to NO2 is both kinetically (reaction rates: 8~40-fold lower than LT-SCR at 423~523 K) and thermodynamically (reaction free energy at 473 K: ~20 kJ mol-1 higher than NO to nitrites) less favorable than NO activation to nitrite intermediates, thus suggesting a relevance of the latter route, rather than NO oxidation to NO2 and subsequent occurrence of fast SCR, to WO3/CeO2-catalyzed LT-SCR reaction cascade.

Keywords NOx, selective catalytic reduction, ceria, low-temperature, reaction mechanism, NO activation