Theoretically, many of the carriers found at present can be used as the carriers of tungstophosphoric acid, but most of them use oxidants as the carriers of oxidants or are easy to decompose when alkali is azeotropic. At present, SiO2, HZSM-5 molecular sieve, Y-type molecular sieve, HP, HMS molecular sieve, worm like molecular sieve, activated carbon, silica gel and so on are the main carriers of phosphotungstic acid catalyst.
At present, the main preparation methods of phosphotungstic acid include impregnation method, adsorption method and sol gel method.
1. Impregnation method
The impregnation method is to dissolve tungstophosphoric acid in water, then impregnate the carrier with this solution and stir it. After a certain period of time, take it out for drying, and then obtain the supported tungstophosphoric acid catalyst. Or the active component is directly loaded on the carrier by physical mixing, hydrothermal dispersion, CO impregnation or ion exchange. However, there are some problems in the stability of the products.
2. Adsorption method
The reflux adsorption method is to add the carrier into the phosphotungstic acid solution, after heating and reflux for a certain time, filter, wash, dry for several hours, and then activate at a certain temperature. The method has good uniformity of the load, but the load is not strong enough and easy to fall off.
3. Sol gel method
Using ethyl orthosilicate as precursor, using alcohol (such as n-butanol, ethanol, etc.) as solvent, inorganic acid (nitric acid, hydrochloric acid, etc.) was used as catalyst for sol gel solution, then added phosphotungstic acid to form gel, drying and standby.
At present, the research on supported tungstophosphoric acid catalyst is still in the primary stage. In order to realize the industrial production of supported tungstophosphoric acid as soon as possible, further research is needed. The main research directions are as follows: further study on the loading mechanism between tungstophosphoric acid and support, especially the mechanism of in-situ synthesis; To solve the problem of dissolution of heteropoly acid in liquid-phase reaction, improve the activity and service life of the supported tungstophosphoric acid catalyst; to study the thermal stability of the supported tungstophosphoric acid catalyst; to study the influence of the modification of the physical and chemical properties of the support on the performance of the supported tungstophosphoric acid catalyst.