Sulfated zirconia nanoparticles synthesized in reverse microemulsions: Preparation and catalytic properties

Microemulsion-derived sulfated zirconia was prepared by addition of zirconium butylate to mixtures of aqueous H2SO4, nonionic surfactants, and heptane as the oil phase and subsequent drying and calcination at 873 K. The resulting catalysts have surface areas ranging from 40 up to 175 m(2) g(-1) depending on the microemulsion composition and show a high activity in n-butane isomerization (4.7 X 10(-7) Mol S-1 g(-1), TOS = 60 min) comparable to that of other commercially available catalysts. The size of the inverse micelles in the microemulsion can be used to tailor the properties of the catalyst in a wide range. In situ X-ray diffraction studies demonstrate significant differences in the crystallization kinetics of materials derived from low and high water/surfactant ratios (R-w). Transmission electron microscope investigations show that a higher degree of crystallite agglomeration and sintering is responsible for lower surface areas of high Rw derived zirconias. According to thermogravimetric studies coupled with mass spectrometry, the lower activity of low Rw derived materials is due to a lower degree of sulfate incorporation. The parameters in the synthesis procedure which affect the activity of the catalyst are systematically studied, and the advantages and limitations of the microemulsion method are discussed.