Promoting effect of Nd on the reduction of NO with NH3 over CeO2 supported by activated semi-coke: an in situ DRIFTS study

Cerium oxides and neodymium-cerium composite oxides were loaded onto activated semi-coke (ASC) by a hydrothermal method for the selective catalytic reduction (SCR) of NO with NH3. The catalytic activity of CeO2/ASC was greatly enhanced by the addition of Nd. The mechanistic cause of the promoting effect of Nd was systematically investigated using various characterization techniques, including XRD, SEM, TEM and in situ DRIFTS. The results revealed that the reaction route for NH3-SCR followed both the E-R and L-H mechanisms over CeO2/ASC and CeO2-Nd/ASC catalysts. Nevertheless, the Nd doping process was beneficial for the formation of Ce3+ and gave rise to the transformation of Lewis acid sites into Bronsted acid sites, which influenced the mechanism of SCR reaction. The generation of oxygen vacancies was in favor of the oxidation of NO to NO2 and thus facilitated the proceeding of the following reduction reactions. Thus, the presence of the Ce3+ state and oxygen vacancies played a primary role in the improvement of the low-temperature SCR performance of the CeO2-Nd/ASC catalyst.