Rational design of porous CexNb1−x oxide hollow nanospheres as a novel NH3-SCR catalyst

Abstract

The morphology and hierarchical structure of materials play an important role in catalytic behaviors. Herein, a series of porous Ce_xNb_1−x (x = 0, 0.2, 0.4, 0.6, 1) hollow nanospheres were designed by a modified seed-mediated growth approach and tested for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). XRD, TEM, BET, Raman, H₂-TPR, NH₃-TPD, XPS and in situ DRIFTS were carried out to explore the physicochemical properties of the prepared bimetal oxides. A strong interaction between Nb₂O₅ and CeO₂ affected the oxygen defects, valence, reducibility, and the number of acid sites. Among the obtained catalysts, the porous Ce_0.4Nb_0.6 nanospheres with more acid sites and excellent reducibility exhibited superior catalytic activity with NO_x conversion of more than 98% in the temperature range of 250–450 °C and high catalytic stability for H₂O and SO₂, which can be attributed to the porous double-shell structure, and the strong interaction of Nb₂O₅ and CeO₂ species. Furthermore, in situ DRIFTS results revealed that the NH₃-SCR reaction on Ce_0.4Nb_0.6 oxide followed the Eley–Rideal mechanism. The results of this work could further provide a strategy for the design and synthesis of materials with hollow and porous structures for various applications.