Study of the morphology and structure of niobia-silica surface oxides using model thin films

• Published in: Journal of catalysis Vol. 108; no. 2; pp. 383 - 400
• Main Authors: Weissman, J.G., Ko, E.I., Wynblatt, P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.12.1987; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; General. Nomenclature, chemical documentation, computer chemistry; Theory of reactions, general kinetics; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Heterogeneous catalysis; Interaction; Niobium V Oxides; Surface analysis; Electron microscopy; Silica; Supported catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(87)90187-4

Model thin films of niobia 4, 12, and 50 Å thick, corresponding to 1, 3, and 13 monolayers, deposited by RF-sputtering onto silica (Nb 2O 5SiO 2), were prepared for a study of the interactions between surface and supporting oxides. These samples were treated in air at 773 and 873 K for up to 16 h and then observed by electron microscopy. For reactively sputtered films, Nb 2O 5 in monolayer and multilayer amounts dewetted the substrate after heating at 773 K, and crystallized to either T- and/or HNb 2O 5 at 873 K. These observations are different from those found for Nb 2O 5SiO 2 high-surface-area samples, prepared by incipient wetness impregnation and similarly treated. In the high-surface-area samples, there is a strong interaction which results in the stabilization of surface-phase Nb 2O 5 at a monolayer coverage and formation of TNb 2O 5 at higher loadings. The difference in behavior between the low- and high-surface-area samples can be understood in terms of stabilization of surface niobia due to surface hydroxyl groups in the latter. These results illustrate the applicability of model thin films to the study of surface oxides.