(120g) Synthesis and Characterization of Mesoporous Semi-Crystalline Mixed Gallium-Niobium Oxide Phases

There has been a great interest in the use of structure-directing surfactant molecules to organize a variety of metal oxide networks into mesoscopically ordered composite materials displaying diverse properties and functionalities. These materials can find applications as heterogeneous catalysts, sensors, electronic and optoelectronic devices. Synthesis of mesoporous mixed transition metal oxides becomes an attractive approach since the high surface area of transition metal oxides with variable oxidation states may act as catalytic active site. Mesoporous gallium oxide and gallium-based oxides are of great interest in the field of heterogeneous catalysis. Different polymorphs of gallium oxide have been employed for the dehydrogenation of alkanes to alkenes, the epoxidation of alkenes in the presence of hydrogen peroxide, and in the aromatization of ethane in the presence of CO₂. Gallium containing metal oxides are active in a number of reactions such as hydrocarbon dehydrogenation, oxydehydrogenation, methane activation etc. Niobium containing oxides are well known as catalysts for different reactions, due to its strong acidic properties. Furthermore, the special properties (redox properties, acidity and catalytic behavior) of compounds containing niobium mixed oxides are of great interest for various catalytic purposes. Herein we present the synthesis and characterization of novel semi-crystalline mesoporous Gallium-Niobium mixed oxide phases prepared in the presence of non-ionic structure directing agents via Self-Assembly Hydrothermal-Assisted (SAHA) method. This method led to the formation of uniform ~ 0.3-2 μm micron-sized mesoporous mixed Gallium-Niobium oxide spheres with narrow size distribution. These mixed mesophases displayed surface areas as high as 360 m²/g and unimodal pore size distribution in the 3-6 nm range. Textural properties such as surface areas and pore size distribution were effectively fine-tuned by the relative concentration of the structure directing agent. Due to their high surface areas, tunability of pore sizes and their acidic nature these mixed mesoporous gallium-niobium oxides could find potential applications as heterogeneous catalysts.

Heterogeneous Catalysis.