Time-resolved in situ DRIFTS study on NH3-SCR of NO on a CeO2/TiO2 catalyst

Abstract

Ce–Ti catalysts were considered as a promising replacement for V–Ti based catalysts for selective catalytic reduction (SCR) of nitrogen oxides (NO and NO₂) with NH₃. In this work, a CeO₂/TiO₂ catalyst was prepared by the impregnation method and studied by a series of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. The results showed that CeO₂ particles grew along TiO₂ faces and amorphous cerium in the lattice of TiO₂, both of which are present on the CeO₂/TiO₂ catalyst. NH₄⁺ might adsorb on the Ti–O–Ce structures or TiO₂–CeO₂ interface as Brønsted acid sites, while two types of NH₄⁺ species were distinguished by the time-resolved spectroscopic method due to the different increasing trends. Based on the temporal evolution transient in situ DRIFTS spectra, L-NH₃ had higher activity than coordinated NH₃ species, which suggested that gas phase NO reacted preferentially with L-NH₃. The NH₄NO₃ intermediate dominated the SCR reactions over the CeO₂/TiO₂ catalyst, which followed the Eley–Rideal mechanism.