Activation of ZrO(2)–WO(3) solid acid catalysts in a Friedel–Crafts reaction through post-hydrothermal treatment

ZrO(2)–WO(3) 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 ZrO(2)–WO(3) catalysts. In this work, poorly reactive ZrO(2)–WO(3) 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 ZrO(2)–WO(3), 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 ZrO(2) crystal from monoclinic to tetragonal as well as a significant increase in acidic WO(x) clusters that anchored onto ZrO(2). The generation of the WO(x) clusters was responsible for the activation of ZrO(2)–WO(3).