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Nanoislands on Nanoislands: Controlling the Dispersion of Barium Oxide on Aluminum Oxide through Successive Ionic Layer Deposition

Thomas I. Gilbert and Johannes W. Schwank. Chemical Engineering, University of Michigan, 2300 Hayward St, 3074 H.H. Dow Building, Ann Arbor, MI 48109-2136

Many catalytic systems show interesting metal-support interactions. However, the complexity of typical supported catalyst systems makes it difficult to isolate these effects. Successive Ionic Layer Deposition enables the organized synthesis of well-defined multilayer catalytic systems. Successive Ionic Layer Deposition (SILD) is an aqueous technique to repeatedly deposit submonolayers of oxide materials on a substrate. With each SILD cycle, aqueous cations and anions are sequentially adsorbed on the substrate to form supported nanoislands or nanofilms. SILD offers the flexibility to systematically choose the deposition rate and surface composition by varying the synthesis conditions and aqueous metal precursors. A dispersed phase of BaO on Al2O3 has been shown to play a major role in NOx emission control catalysis for lean burn engines.[1] However, conventional catalyst synthesis techniques tend to produce both bulk and disperse phases of BaO on Al2O3. SILD offers the opportunity to exclusively produce the dispersed phase of BaO on Al2O3 and study its performance. In this paper, we describe how SILD was used to first deposit nanoislands of Al2O3 on silicon wafer supports and then deposit nanoislands of BaO onto the Al2O3. These model catalyst systems deposited on planar supports were characterized by Atomic Force Microscopy, Scanning Electron Microscopy, and X-ray Photoelectron Spectroscopy. FIGURE: Atomic Force Microscopy image of BaO nanoislands on larger Al2O3 nanoislands supported on a silicon wafer synthesized by SILD and thermally treated to 450 degC. REFERENCE 1. X. Chen, J. Schwank, J. Li, W.F. Schneider, C.T. Goralski, P.J. Schmitz, Appl. Catal. B Environ. 61 (2005).