Cation Movements during Dehydration and NO2 Desorption in a Ba-Y,FAU zeolite: an in situ Time-resolved X-ray Diffraction Study

Journal Article · Thu Feb 28 04:00:00 EST 2013 · Journal of Physical Chemistry C, 117(8):3915-3922

DOI:https://doi.org/10.1021/jp308307m· OSTI ID:1068647

Wang, Xianqin; Hanson, Jonathan C; Kwak, Ja Hun; Szanyi, Janos; Peden, Charles HF

Synchrotron-based in situ time-resolved X-ray diffraction and Rietveld analysis were used to probe the interactions between BaY, FAU zeolite frameworks and H2O or NO2 molecules. These results provided information about the migration of the Ba2+ cations in the zeolite framework during dehydration and during NO2 adsorption/desorption processes in a water free zeolite. In the hydrated structure water molecules form four double rings of hexagonal ice-like clusters [(H2O)6] in the 12-ring openings of the super-cage. These water rings interacted with the cations and the zeolite framework through four cation/water clusters centered over the four 6-membered rings of the super-cage (site II). Interpenetrating tetrahedral water clusters [(H2O)4] and tetrahedral Ba+2 cation clusters were observed in the sodalite cage. Consistent with the reported FT-IR results, three different ionic NOx species (NO+, NO+-NO2, and NO3-) were observed following NO2 adsorption by the dehydrated Ba-Y,FAU zeolite. The structure of the water and the NOx species were correlated with the interactions between the adsorbates, the cations, and the framework. The population of Ba2+ ions at different cationic positions strongly depended on the amount of bound water or NOx species. Both dehydration and NO2 adsorption/desorption resulted in facile migration of Ba2+ ions among the different cationic positions. Data obtained in this work have provided direct evidence for the Ba2+ cation migration to accommodate the binding of gas molecules. This important feature may play a pivotal role in the strong binding of NO2 to Ba-Y,FAU zeolite, a prerequisite for high catalytic activity in lean NOx reduction catalysis.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1068647
• Report Number(s): PNNL-SA-90332; 35404; VT0401000
• Journal Information: Journal of Physical Chemistry C, 117(8):3915-3922, Journal Name: Journal of Physical Chemistry C, 117(8):3915-3922
• Country of Publication: United States
• Language: English

Related Subjects

Environmental Molecular Sciences Laboratory
NOx reduction
cation location
synchrotron x-ray diffraction
zeolites