Acidic properties of oxides containing niobia on silica and niobia in silica

• Published in: Journal of catalysis Vol. 129; no. 1; pp. 38 - 46
• Main Authors: Burke, P.A., Ko, E.I.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.05.1991; Elsevier
• Subjects: 01 COAL, LIGNITE, AND PEAT; 010408 - Coal, Lignite, & Peat- C1 Processes- (1987-); 02 PETROLEUM; 020400 - Petroleum- Processing; 10 SYNTHETIC FUELS; 100200 - Synthetic Fuels- Production- (1990-); 400201 - Chemical & Physicochemical Properties; ADSORPTION; ALCOHOLS; AZINES; BROENSTED ACIDS; CARBON COMPOUNDS; CARBON MONOXIDE; CARBON OXIDES; Catalysis; CATALYSTS; Catalysts: preparations and properties; CHALCOGENIDES; CHEMICAL ANALYSIS; CHEMICAL PREPARATION; CHEMICAL REACTIONS; Chemistry; COMPOSITE MATERIALS; COPRECIPITATION; CRYSTAL STRUCTURE; DEHYDRATION; DEHYDROGENATION; DISPERSIONS; ETHANOL; Exact sciences and technology; General and physical chemistry; GRAVIMETRIC ANALYSIS; HETEROCYCLIC COMPOUNDS; HYDROGEN COMPOUNDS; HYDROXY COMPOUNDS; IMPREGNATION; INFRARED SPECTRA; INORGANIC ACIDS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ISOMERIZATION; LAYERS; LEWIS ACIDS; MATERIALS; METHANATION; MICROSTRUCTURE; MINERALS; MIXTURES; NIOBIUM COMPOUNDS; NIOBIUM OXIDES; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PHASE STUDIES; PRECIPITATION; PYRIDINE; PYRIDINES; QUANTITATIVE CHEMICAL ANALYSIS; QUANTITY RATIO; REFRACTORY METAL COMPOUNDS; SEPARATION PROCESSES; SILICA; SILICON COMPOUNDS; SILICON OXIDES; SORPTION; SPECTRA; SURFACE PROPERTIES; SYNTHESIS; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; THERMAL ANALYSIS; THERMAL GRAVIMETRIC ANALYSIS; TRANSITION ELEMENT COMPOUNDS; Monolayer; Impregnation; Niobium Silicon Oxides Mixed; Acidic site; Acidity; Structure; Heat of adsorption; Coprecipitation
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(91)90007-Q

A series of composite oxides containing niobia (Nb 2O 5) and silica (SiO 2) was prepared by either incipient wetness impregnation to form surface phase oxides or by coprecipitation to form mixed oxides. At low Nb 2O 5 concentrations, both the surface phase and mixed oxides showed strong Lewis acidity as determined by thermogravimetric and infrared studies of adsorbed pyridine. A surface phase oxide containing 0.25 monolayer of Nb 2O 5 on SiO 2 further showed strong Brønsted acidity. With increasing Nb 2O 5 concentration and/or treatment temperature, Nb 2O 5 in these composite oxides became more bulk-like and showed a corresponding decrease in acid strength. These acidic properties are discussed in terms of proposed structural models which contain tetrahedral niobia, octahedral niobia, and Nb0 bonds as basic building blocks.