New approach to preparation and investigation of active sites in sulfated zirconia catalysts for skeletal isomerization of alkanes
Section snippets
INTRODUCTION
Great interest in the development and investigation of novel catalysts for isomerization of normal butane to isobutane is stimulated by an increasing demand in isobutane and isobutene used as precursors for preparation of high-octane and ecologically benign gasoline components – methyl-tert-butyl ether and alkylates. Sulfated zirconia catalysts are some of the most promising new materials suggested for this purpose. The interest to these materials was characterized by an exponential growth in
Samples
Zirconium dioxide and zirconium-calcium (or barium) oxide composites were prepared by precipitation from solutions of corresponding nitrates with aqueous bases at definite pH and temperature followed by washing, drying and calcination according to [8]. The final thermal treatment was calcination at 700°C in dry air flow for 4 h. Then, the samples were subjected to incipient wetness impregnation with ammonium sulfate (Fisher, Certified A.C.S.) to yield nominal SO3 loading of 8 wt.%, dried at
RESULTS AND DISCUSSION
Table 1 presents the results of the XRD analysis of zirconia-based materials before and after the sulfation stage. The materials were prepared using different types and amounts of alkaline earth metal oxides and different precipitation pHs. In good agreement with earlier reported data [7], introduction of a small amount of Ca (as low as 5 mol.%) results in the formation of a cubic solid solution Zr1-xCaxO2-x. An increase of the CaO concentration to 10 mol.% leads to complete disappearance of
ACKNOWLEDGEMENTS
This work has been supported by the Russian Foundation for Basic Research (Grants 00-03-32441 and 00-15-97440).
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