Preparation and Catalytic Evaluation of Macroporous Crystalline Sulfated Zirconium Dioxide Templated with Colloidal Crystals

Abstract

Colloidal crystal templates were used to synthesize three-dimensionally ordered macroporous sulfated zirconia catalysts with pore diameters of ∼300 nm and less. Ordered arrays of uniformly sized poly(methyl methacrylate) latex spheres were infiltrated with clear precursor solutions containing varying SO4/Zr molar ratios. After solidification of the material in the void space between the spheres, the polymer templates were removed by calcination at various temperatures, producing crystalline sulfated zirconia replicas of the template arrays. The effects of changing sulfate content and calcination temperature on the physicochemical properties of the material (including shrinkage, grain size, surface area, and composition) were systematically studied. The presence of sulfate retarded the crystallization and crystal growth, which enabled greater control of macropore shrinkage and periodic order of the material. The combination of crystal growth inhibition and the inherent porosity of the PMMA latex are believed to be the major factors contributing to the observed BET surface areas of the materials, which were significantly larger than those of their nontemplated counterparts and passed through a maximum as a function of calcination temperature and initial SO4/Zr ratio. The maximum value of 123 m2/g was attained by a sample with SO4/Zr = 2, calcined at 650 °C, with a sulfate surface coverage of 3.1 nm-2. The n-butane isomerization activity of the material also passed through a maximum as a function of calcination temperature and initial SO4/Zr ratio, reaching its maximum value for a sample with SO4/Zr = 2, calcined at 600 °C.