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

Abstract

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.