Modification Of Tungsten - Zirconium Solid Acid Catalyst And Its Application In Esterification

Solid superacid catalyst is a new type of catalytic materials which have been developed in recent years. This catalyst has been proved to be very effective from the viewpoint of activity, selectivity and reusability in the synthesis of various important chemicals involved with a series of difficulties using traditional liquid acid catalysts. It can resist corrosion, and overcome some problems of separation, transport, storage, and pollution. Metal oxide catalysts with many advantages, such as strong acidity, thermal stability and excellent catalytic properties, has been inverstigated by the researchers and became the active research field of solid superacid catalystsIn the first part of this paper, a new type of WO3/B2O3-ZrO2 solid superacid catalyst was prepared by co-precipitation method under the condition of constant pH. Its physical properties were investigated by some analytical methods, such as FT-IR, TPD, XRD, Raman and DSC-TG. The results show that the introduction of B active components improved the strength of acid and increased the amount of acid sites. The formation of acid center for ZrO2 crystalline phase was very important and was observed at the calcinations temperature, meanwhile the crystal transition temperature of ZrO2 increases. The optimum preparation conditions of WO3/B2O3-ZrO2 catalysts were:mass percentage content of W was 20% and B was 7%, pH=9, calcination at 973K for 3h in the atmosphere.In the second section of the paper, a low poisonous, high performance, wide application preservative nipagin ester was introduced and it was synthesized with the homemade solid superacid catalyst, which avoided the drawbacks in the industrial synthesis with H2SO4 as catalyst. The activity of the synthesis of paraben over the WO3/B2O3-ZrO2 catalysts was studied and the results showed that the highest yield of ethyl paraben was observed under the influences of reaction time, temperature, raw materials ratio, the quantity of catalyst and recycling use performance of catalyst were investigated. The optimum synthetic conditions of ethylp-hydroxybenzoate were:mole ratio of acid to ethanol was 1:7, mass ratio of acid to catalyst was 7:1, and refluxing time was 4h.To further improve the catalytic performance of WO3/B2O3-ZrO2, in the third part, Ce was added to modify WO3/B2O3-ZrO2 catalysts, and it was characterized by XRD, NH3-TPD, Raman, FT-IRand TG-DSC. Results showed that Ce was introduced into ZrO2 lattice and improved performance of catalyst. The addition of Ce did not change the structure of ZrO2 crystal and tungsten oxide. Compared to WO3/B2O3-ZrO2 catalyst, this catalyst has stronger acid strength, more L acid sites. And the optimum mole ratio of Ce/Zr was 1:15.In the fourth part, the catalytic and reusable performances of WO3/B2O3-ZrO2 and Ce-WO3/B2O3-ZrO2 catalysts were examined in the synthesis of plasticizer ester—maleic diester. The results showed that, compared with WO3/B2O3-ZrO2, modified Ce-WO3/B2O3-ZrO2 catalysts showed higher catalytic activity, so proper doping could enhance catalytic activity of WO3/B2O3-ZrO2 catalysts. Experimental results showed that Ce-WO3/B2O3-ZrO2 catalyst was a good catalyst for the synthesis of maleic diester. Then Ce-WO3/B2O3-ZrO2 catalysts were used to synthesize maleic diester, among them, the yield of diisoamyl maleate was highest, afterwards the optimum synthetic condition parameters of diisoamyl maleate were determined as follows: mole ratio of acid to isoamyl alcohol 1:4, mass ratio of acid to catalyst 5:1, and refluxing time was 3h. Thereby an environmental friendly approach for the synthesis of this ester was provided.