Activated Carbon Supported Silver Phosphomolybdate Tungsten Heteropolyacid Catalyst

Ketal is an important intermediate in chemical industry. It is often used for the protection of ketones and even as a special reaction solvent. Ketal is superior to parent carbonyl compounds in floral and fruity aroma, most of which have special aroma. As a new type of perfume, ketal has been widely used in daily chemical and food industries in recent ten years.

The traditional method of ketal synthesis is the direct dehydration of ketone and alcohol under the catalysis of inorganic acids (such as sulphuric acid, hydrochloric acid and phosphoric acid). The yield of inorganic acid reaction is high, but all of them have strong corrosiveness, serious equipment corrosion, three wastes pollution and troublesome post-treatment.

Among the existing technologies, heteropoly acid catalysts supported on activated carbon have attracted much attention because of their strong acidity, high activity at low temperatures, acidity and oxidation properties. Some scholars have published papers on the preparation of silver heteropoly acid catalysts supported on activated carbon, such as phosphomolybdenum tungsten.

(1)Activated carbon particles with a diameter of 75-800 microns were added into 10%-20% HNO₃ aqueous solution until the HNO₃ solution was immersed in activated carbon; the activated carbon particles were heated and refluxed, then washed with cooling water to be pH neutral; filtered; and then dried to constant weight at 80-150 ℃ for reserve.

(2)The H₃PW₆Mo₆O₄₀ solution with concentration of 10%-20% was prepared by mixing 95% ethanol with water in the same volume as solvent.

(3)The activated carbon particles treated in step (1) were added to the phosphomolybdenum tungsten heteropoly acid solution prepared in step (2) at the ratio of 1:0.1-0.8, stirred, and then dripped into 10%-20% AgNO₃ solution of 1-4 times the quality of phosphomolybdenum-tungsten heteropoly acid. The silver salt of phosphomolybdenum-tungsten heteropoly acid to be precipitated was loaded by activated carbon particles.

(4)The loaded activated carbon particles were placed in the drying chamber and dried at 90-100 ℃ for 1-10 hours (preferably 2-5 hours), then cooled in the dryer to obtain the activated carbon supported silver phosphomolybdenum tungsten heteropoly acid catalyst.

A series of catalysts with a wide range of loads can be synthesized by precipitation and adsorption, and the loads are synchronized with the formation of silver salts. This kind of silver heteropoly acid catalyst supported on activated carbon has high activity because of its granularity and easy treatment after reaction, which overcomes the shortcomings of low specific surface area of Heteropoly acid.

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