Activation of ZrO2–WO3 solid acid catalysts in a Friedel–Crafts reaction through post-hydrothermal treatment

ZrO2-WO3 mixed oxide plays an essential role in the chemical and petroleum industries. So far, very little work has paid attention to the activation of the low activity of ZrO2-WO3 catalysts. In this work, poorly reactive ZrO2-WO3 was prepared as a model catalyst by a sol-gel method and it was accompanied by post-hydrothermal treatment with various solutions. The catalytic results in the Friedel-Crafts reaction of anisole and benzyl alcohol showed that the post-hydrothermal treatment with ethylenediamine or ammonium hydroxide solutions dramatically improved the activity of ZrO2-WO3, while the hydrothermal treatments with water or ammonia chloride solution resulted in poorer activity and selectivity. The former treatments were found to induce a huge transformation of the ZrO2 crystal from monoclinic to tetragonal as well as a significant increase in acidic WO x clusters that anchored onto ZrO2. The generation of the WO x clusters was responsible for the activation of ZrO2-WO3.