The lean NOₓ traps behavior of (1–5%) BaO/CeO₂ mixed with Pt/Al₂O₃ at low temperature (100–300°C): The effect of barium dispersion
2013
Lv, Liangfang | Wang, Xinquan | Shen, Meiqing | Zhang, Qingqing | Wang, Jun
The present work investigates the lean NOₓ trapping performance of BaO (1, 3, 5wt.%) modified CeO₂ (BC) NOₓ storage catalysts, where 2wt.% Pt/Al₂O₃ (PA) part was mechanically blended in. Before mixture, the storage catalysts (BaO/CeO₂) were treated at 800°C for 5h in a steam and CO₂-containing air. The storage catalysts were characterized in detail by X-ray diffraction (XRD), nitrogen adsorption–desorption, energy-filtered transmission electron microscopy (EFTEM), and X-ray photoelectron spectroscopy (XPS). Results show highest Ba dispersion on CeO₂ for 3BC sample. 5BC sample forms large BaCO₃ particle leading to lower Ba dispersion than 3BC sample. NOₓ storage capacity was investigated in steady-state and transient NO/O₂ adsorption reactions in the temperature range from 100°C to 300°C. As BaO loading increases, the PA–BC catalysts exhibit nonlinear enhancement for NOₓ storage capacity (NSC) compared with PA–Ce sample. And PA–3BC sample possesses superior NOₓ storage capacity. The evolution and stability of NOₓ adsorbed species at 100°C were explored by in situ DRITFS. DRIFTS results show that PA–3BC and PA–5BC samples present obviously different NOₓ adsorbed species from PA–Ce sample. Besides, nitrate formation is more facilitated for PA–3BC sample compared with the PA–5BC sample. These results can be contributed to high Ba dispersion on CeO₂, which is advantageous to Ba–Ce contact and NOₓ trapping. And the Ba sites in intimate contact with CeO₂ can effectively utilize the Ba sites and oxygen from CeO₂ to form nitrates at low temperature, which possess higher stability than Ce nitrates.
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