Effect of hydrothermal aging on NO_x reduction performance for Sb–V–CeO₂/TiO₂ catalyst

Herein, we investigated the NO_x reduction performance of Sb–V–CeO₂/TiO₂ (SbVCT) catalyst subjected to hydrothermal aging, where 6 vol% of H₂O was fed to the SbVCT for 16 h with variable temperatures of 550–750 °C. The structural, morphological, redox, and acid properties of fresh and aged catalysts were comprehensively characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, N₂-physisorption, temperature programmed reduction/desorption (H₂–TPR/NH₃/NO–TPD) and in situ DRIFTS. The XRD, Raman and TEM results of the fresh and the one hydrothermally aged at 550, 600 °C catalysts indicated the presence of finely dispersed polymeric vanadia, antimony, and nano-crystalline ceria species on TiO₂ support. The SbVCT catalysts hydrothermally aged at the temperatures ≤ 600 °C showed better NO_x conversions than the others aged > 600 °C. This was because aging at the temperatures ≤ 600 °C could help to minimize the loss of surface redox/acid properties that were originally inherent to surface vanadyl and CeO₂ species that went into CeVO₄ and large CeO₂ aggregates. This in turn led to the loss of surface redox and acidic characters indigenous to the SbVCT and reduced its NO_x reduction performance. Moreover, the NO_x reduction performance of hydrothermally aged V–WO₃–TiO₂ catalyst, when compared with that of SbVCT catalyst, showed relatively low NO_x conversions at the temperatures below 300 °C.