Model studies of BaO/Al2O3 NOx storage materials

COLL 448

Charles H. F. Peden,, Cheol Woo Yi,, Emrah Ozensoy,, and Janos Szanyi, Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, PSL, MS K2-12, P. O. Box 999, Richland, WA 99352
New approaches toward NOx reduction in fuel-efficient oxygen-rich environments are being explored with one of the most promising being the NOx storage/reduction technology based on barium oxide-based catalyst materials. In recent studies of realistic Al2O3-supported BaO-based materials, we identified the nature of NOx species formed during NO2 adsorption. Two fundamentally different nitrate species were identified; surface nitrates on the monolayer of BaO covering the Al2O3 support surface, and bulk-like Ba(NO3)2 that forms in the reaction of NO2 with BaO in excess of that needed for the monolayer coverage. We have also determined how the morphology of the Ba-containing phase changes during the catalyst activation, NO2 uptake/NOx release cycles, and how water, a major component of the exhaust gas mixture, effects this morphology. Although the real catalytic systems have been studied extensively during the last decade, model systems that allow understanding of the basic processes on the atomic level have attracted much less attention. In our laboratory we have been performing model studies of the structural and chemical properties of BaO deposited onto very thin Al2O3 films grown on NiAl single crystal substrates, using primarily TPD, reflection absorption infrared spectroscopy (RAIRS) and XPS. The results obtained on these model systems will be compared to those obtained from high surface area BaO/γ-Al2O3 NOx storage materials.