Preparation of novel CeMo(x) hollow microspheres for low-temperature SCR removal of NOx with NH3

Abstract

A series of novel Mo doped CeO₂ hollow microspheres have been successfully synthesized using carbon microspheres as templates, which were characterized by XRD, SEM, TEM, BET and used to selective catalytic reduction (SCR) of NO_x with ammonia at lower temperature. Compared with pure CeO₂ hollow microspheres, Mo doped CeO₂ hollow microspheres showed a better catalytic performance from 200–400 °C. The optimal molar ratios of Mo/Ce and surface active sites to remove NO_x were also investigated, which can significantly affect the catalytic performances. Among all the hollow microspheres with different molybdenum doping ratios, the obtained CeMo(0.3) hollow microspheres showed not only the best SCR performance at lower temperature but also excellent stability and H₂O resistance, which was attributed to the higher Brønsted acid sites and reasonable Ce³⁺ content and chemisorbed oxygen species, and the synergic effect between CeO₂ and MoO₃ based on the XPS, NH₃-TPD, H₂-TPR and in situ DRIFTS results. Additionally, according to the reactivity of adsorbed NH₃ and NO_x species based on in situ DRIFTS, the excellent low-temperature NH₃-SCR activity of CeMo(0.3) hollow microspheres was resulted from the reactivity of the more active NH₄⁺ ions with gaseous NO₂ molecules (i.e., the “fast SCR” reaction).