Structural modification of zirconia and its influence on the catalytic activity

X-ray diffraction, differential thermal analysis and specific surface area measurements have been employed to understand the structural properties of ZrO₂ and sulphate-modified ZrO₂ calcined at different temperatures. Calcination facilitates the transformation of ZrO₂ from cubic to monoclinic phase. Addition of SO₄ ion to Zr(OH)₄ helps to retain the cubic phase up to 550 °C, and to maintain the surface area through a surface complex formation mechanism. The modified ZrO₂ acts as a superacid catalyst and enhances the vapour-phase aniline alkylation.