Polyoxometalate-based acid salts with tunable separation properties as recyclable Brönsted acid catalysts for the synthesis of β-keto enol ethers

► Polyoxometalate-based acid salts catalyzed synthesis of β-keto enol ethers. ► Self-separation or heterogeneous catalysis occurred. ► The catalyst conveniently separated with the products and easily recycled. ► There was no considerable loss in catalytic activity after several reaction cycles. ► Various β-keto enol ethers were obtained in high to excellent yields.