Niobium Tungstate Preparation by Solution Thermal Method

Solid acid catalytic materials have attracted more and more attention because of their unique structure. Niobium tungstate, as a typical solid acid catalytic material, exhibits good catalytic activity, selectivity and stability in some organic synthesis reactions. In addition, due to its unique structure and physicochemical properties, niobium tungstate compounds have attracted widespread interest in piezoelectric, dielectric and thermodynamic aspects.

Nowadays, the preparation of niobium tungstate is based on high temperature solid state method. High temperature solid state method needs repeated high temperature burning and grinding. The temperature is above 1000K. The products are all aggregates. The increase of particle size and sintering phenomenon caused by high temperature burning are inevitable. The liquid phase method is more convenient to control the size, morphology and particle size distribution of the product phase under relatively mild conditions. Therefore, some scholars use solution thermal method to prepare Nb tungstate, which includes the following steps:

1.0 g Nb₂O₅ and 5.0 g KOH were added into 60 ml deionized water and treated for 2 days at 180 ℃. After hydrothermal reaction of 2.4 ml, [Nb6O19] 8-solution in the upper and middle layers of the product was added with 20 ml octanol, 0.1673 g H₂WO₄ was added according to the molar ratio of Nb₅+:W₆+=1:2.5, and then the solution was adjusted by dilute hydrochloric acid to pH=7.2. The solution was put into a 40 ml reactor and treated with water at 220 ℃ for 2 days. The product was centrifugally cleaned by deionized water and dried.

Because the solvent in the reactor is in the supercritical state, the solution thermal method has many advantages over the solid-phase synthesis method, such as low reaction temperature, simple process, high reactant activity, fast reaction rate, etc. Moreover, the commonly obtained particles have good crystallinity, uniform fine dispersion, and are easy to change the scale of the product phase through the reaction conditions. The size, morphology and particle size distribution were controlled to improve the properties of the product. The highly insoluble Nb₂O₅ was converted into a soluble [Nb₆O₁₉] ₈^-niobium source by hydrothermal pretreatment at room temperature and pressure, and a very good reaction effect was obtained.

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