Synthesis of DL-Tartaric Acid from Maleic Anhydride Over SiO₂-Modified WO₃-ZrO₂ Catalyst

In this work, the addition of 5%SiO2 to 7.5%WO3-ZrO2 catalyst increased the content of tetragonal ZrO2 and BET, which could promote the formation of W-O-Zr(Si) bonds between WOx species and 5%SiO2-ZrO2 material, thus reducing the degree of aggregation of WOx species. The oligomerized WOx species on the 7.5%WO3-5%SiO2-ZrO2 catalyst could not only remain stable, but also provided stable Lewis acid for the activation of hydrogen peroxide and maleic anhydride for epoxidation. In addition, the Si-O-Zr bond on SiO2-modified 7.5%WO3-ZrO2 catalyst could provide an additional Bronsted acid site for activating the hydrolysis of epoxysuccinic acid to DL-tartaric acid. Therefore, the DL-tartaric acid yield of SiO2-modified 7.5%WO3-ZrO2 catalyst was higher than that of 7.5%WO3-ZrO2 catalyst, and also higher than that of Na2WO4 catalyst.