Catalyst size and morphological effects on the interaction of NO₂ with BaO/γ-Al₂O₃ materials

Journal Article · Tue Jun 01 00:00:00 EDT 2010 · Catalysis Today

DOI:https://doi.org/10.1016/j.cattod.2010.01.005· OSTI ID:984221

Mei, Donghai; Kwak, Ja Hun; Szanyi, Janos; Ge, Qingfeng; Peden, Charles H. F.

The capability of NO_x storage on the supported BaO catalyst largely depends on the Ba loading. With different Ba loadings, the supported BaO component exposes various phases ranging from well-dispersed nanoclusters to large crystalline particles on the oxide support materials. In order to better understand size and morphological effects on NO_x storage over γ-Al₂O₃-supported BaO materials, the adsorption structures and energetics of single NO₂ molecule, as well as NO_x + NO_y (NO₂ + NO₂, NO + NO₃ and NO₂ + NO₃) pairs on the BaO/γ-Al₂O₃(1 0 0), (BaO)2/γ-Al₂O₃(1 0 0), and (BaO)₅/γ-Al₂O₃(1 0 0) surfaces were investigated using first-principles density functional theory calculations. A single NO₂ molecule prefers to adsorb at basic OBa site forming anionic nitrate species. Upon adsorption, a charge redistribution in the supported (BaO)_n clusters occurs. Synergistic effects due to the interaction of NO₂ with both the (BaO)n clusters and the γ-Al₂O₃(1 0 0) support enhance the stability of adsorbed NO₂. The interaction between NO₂ and the (BaO)_n/γ-Al₂O₃(1 0 0) catalysts was found to be markedly affected by the sizes and morphologies of the supported (BaO)_n clusters. The adsorption energy of NO₂ increases from -0.98 eV on the BaO/γ-Al₂O₃(1 0 0) surface to -3.01 eV on (BaO)₅/γ–Al₂O₃(1 0 0). NO₂ adsorption on (BaO)₂ clusters in a parallel configuration on the γ-Al₂O₃(1 0 0) surface is more stable than on dimers oriented in a perpendicular fashion. Similar to the bulk BaO(1 0 0) surface, a supported (BaO)_n cluster-mediated electron transfer induces cooperative effects that dramatically increase the total adsorption energy of NO_x + NO_y pairs on the (BaO)_n/γ-Al₂O₃(1 0 0) surfaces. Following the widely accepted NO₂ storage mechanism of BaO + 3NO₂(g) → Ba(NO₃)₂ + NO(g), our thermodynamic analysis indicates that the largest energy gain for this overall process of NOx uptake is obtained on the amorphous monolayer-like (BaO)₅/γ-Al₂O₃(1 0 0) surface. Finally, this suggests that γ-Al₂O₃-supported BaO materials with ~6–12 wt% loadings may provide optimum structures for NO_x storage.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 984221
• Report Number(s): PNNL-SA-68739; 34000; 33216; 35404; TRN: US201015%%877
• Journal Information: Catalysis Today, Vol. 151, Issue 3-4; ISSN 0920-5861
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ADSORPTION
CATALYSTS
CONFIGURATION
DIMERS
ELECTRON TRANSFER
FUNCTIONALS
NITRATES
OXIDES
STABILITY
STORAGE
THERMODYNAMICS
BARIUM OXIDES
NITROUS OXIDE
MATERIALS
Nitrogen oxides
barium oxide
alumina
adsorption
density functional theory
Environmental Molecular Sciences Laboratory