In this investigation, Pt–Ba–Ce/γ-Al₂O₃ catalysts were prepared by incipient wetness impregnation and experiments were performed to evaluate the influence of H2 on the evolution mechanism of nitrogen oxides (NO_x) storage and reduction (NSR). The physical and chemical properties of the Pt–Ba–Ce/γ-Al₂O₃ catalysts were studied using a combination of characterization techniques, which showed that PtO_x, CeO₂, and BaCO₃, whose peaks were observed in X-ray diffraction (XRD) spectra, dispersed well on the γ-Al2O3, as shown by transmission electron microscope (TEM), and that the difference between Ce³⁺ and Ce⁴⁺, as detected by X-ray photoelectron spectroscopy (XPS), facilitated the migration of active oxygen over the catalyst. In the process of a complete NSR experiment, the NO_x storage capability was greatly
enhanced in the temperature range of 250–350 °C, and reached a maximum value of 315.3 μmol·g⁻¹_cat at 350 °C, which was ascribed to the increase in NO₂ yield. In a lean and rich cycling experiment, the results showed that NO_x storage efficiency and conversion were increased when the time of H₂ exposure (i.e., 30 s, 45 s, and 60 s) was extended. The maximum NO_x conversion of the catalyst reached 83.5% when the duration of the lean and rich phases was 240 and 60 s, respectively. The results revealed that increasing the content of H₂ by an appropriate amount was favorable to the NSR mechanism due to increased decomposition of nitrate or nitrite, and the refreshing of trapping sites for the next cycle of NSR.