Insights into the role of a structural promoter (Ba) in three-way catalyst Pd/CeO₂–ZrO₂ using in situ DRIFTS

Abstract

A series of Pd/CeO 2 -ZrO 2 (Pd/CZ) catalysts modified with barium oxide with different contents were prepared and characterized by XRD, BET, XPS, H 2 -TPR and NO x adsorption/desorption-MS. In particular, the effect of a structural promoter (Ba) on the catalytic and surface behaviour was investigated by means of in situ DRIFTS. Doped Ba enters into the CeO 2 lattice, and thus results in the formation of more homogenous Ce-Zr-Ba ternary solid solution, which enhances the textural/structural thermostability and NO x storage efficiency of the catalysts. DRIFTS results indicate that the introduction of Ba weakens the strong adsorption of HC reactants on the surface of the catalysts. Furthermore, the addition of Ba accelerates the dissociation of NO and facilitates the formation of intermediates (NCO and CN) due to the outstanding electron-donating ability of Ba. Therefore, the Ba modified catalysts present much higher catalytic activity for HC and NO x conversions compared with Pd/CZ. However, the addition of Ba inhibits the oxidation of CO at low temperatures resulting from the decreased amount of active sites. In addition, the NO x operation window is widened with increasing Ba content due to the enhanced NO x storage capacity. † Electronic supplementary information (ESI) available: The BJH pore size distribution of fresh and aged catalysts, and the in situ DRIFTS spectra of Pd/ CZB3 and Pd/CZB9 catalysts under simulated reaction conditions. See

Recent advances in gasoline three-way catalyst formulation: A review

“…Yang et al 42 and Lan et al 43 looked into the addition of BaO to Pd/CeO 2 -ZrO 2 and Pd/CeO 2 -ZrO 2 -Al 2 O 3 , respectively. Yang et al found that it was possible to synthesize a homogeneous single-phase Ce/Zr/Ba solid solution with enhanced reducibility.…”

Structure, synthesis, and catalytic properties of nanosize cerium-zirconium-based solid solutions in environmental catalysis

“…After thermal aging treatment, Zr-rich catalysts (CeO2/ZrO2 < 1) underwent less severe deterioration of the catalytic activity compared with Ce-rich catalysts (CeO2/ZrO2 ≥ 1) due to better thermal stability, and Pd/Ce0.5Zr0.5O2BaO presented the optimally catalytic performance. Subsequently, they probed the role of Ba in TWCs Pd/Ce0.5Zr0.5O2 using in-situ DRIFTS [481]. The introduction of Ba weakened the strong adsorption of HC reactants on the catalyst surface and accelerated NO dissociation.…”

Pd model catalysts: Effect of aging duration on lean redispersion

“…The XPS spectra of the fresh and redox aged Pd/CZO samples are shown in Figure 3. The Pd 3d peaks were fit under the raw data between the shoulders of the Zr 3p peaks as is typically performed for analysis of Pd on CZO support [48,49,50,51]. The fresh Pd/CZO sample had two Pd 3d 5/2 peaks, at 334.7 eV for Pd metal and at 337.1 eV for Pd +2 .…”