Ammonium Metatungstate Hydrotalcite Catalyst
In recent years, solid acid alkali catalysis of gas-solid-phase reaction of alkylation of catechols has attracted attention due to the environmentally friendly economy and overcoming the environmental pollution, separation and recovery difficulties and equipment corrosion and other defects, compared to conventional synthesis methods, and has shown significant advantages in saving resources and improving economic efficiency. It is found that Al-Ti-P-O, Al-Ti-Si-P-O and silica-supported ammonium metatungstate (AMT/SiO2) catalyst exhibited high catalytic activity. 
Hydrotalcite is a kind of anionic clay with layered structure, because of its special layered structure and high catalytic performance in acid-base catalysis, condensation, addition polymerization, hydrogenation and alcohol conversion reaction, hydrotalcite has attracted many concerns. The exchangeable property of hydrotalcite anions make all kinds of anions (such as metatungstate ion) can be introduced into the interlayer of hydrotalcite in succession, thus to form a large class of materials - pillared hydrotalcite layered material.
A study has pointed out a preparation method of ammonium metatungstate hydrotalcite catalyst, and studied its catalytic performance, while the preparation steps are as follows:
1. synthesis of hydrotalcite material, take the raw material of magnesium nitrate hexahydrate, aluminum nitrate and sodium hydroxide, and to control the final pH value among 8 ~ 10 of the system, then go on aging, filtration and washing to get hydrotalcite NO3-MgAl;
2. Weigh a certain amount of fresh prepared hydrotalcite NO3-MgAl to disperse in distilled water, stirring at room temperature for overnight to fully expand;
3. Add dilute nitric acid dropwise to adjust the pH value of hydrotalcite slurry among 5.5~6, then rise the temperature to 348K;
4. Rapidly add ammonium metatungstate solution under the condition of stirring, and to react at 348K for 2 to 3 hours, then pumping wash the sample and dry at 348K to get the ammonium metatungstate hydrotalcite catalyst, i.e. AMT-Mg2Al.
The results showed that after changed with AMT, hydrotalcite will exhibit activity to the reaction of gas-solid phase reaction of catechol and methanol, while the conversion of catechol is 75%, the selectivity of guaiacol is 90%, but the catalytic activity decays.
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