Synthesis, characterization, and light n-alkane isomerization activity of mesoporous sulfated zirconia catalysts

The preparation of a high surface area, mesoporous sulfated zirconia catalyst has been investigated by direct and secondary synthesis procedures. The synthesized materials have been characterized by XRD, N₂ BET, N₂ adsorption, TGA/DTA, FTIR, XPS, and SEM. Synthesis by a surfactant assisted method reported for the silica MCM-41 structure was extended to zirconia. However, thermally stable mesoporous zirconia was not obtained by this method. A method of preparing a novel, non-uniform, disordered mesoporous sulfated zirconia catalyst via a surfactant free synthesis was developed. Refluxing a slurry of freshly precipitated hydrous zirconia at 90°C produces a mesoporous zirconia with a surface area of approximately 500 m2/g prior to sulfating and calcining. Mesoporous sulfated zirconia catalysts prepared from this zirconia have surface areas of approximately 250 m2/g. Conventional sulfated zirconia catalysts typically measure 100–120 m 2/g.; The mesoporous sulfated zirconia catalysts are thermally stable under reaction conditions and are active for n-butane isomerization. XRD shows no long range order tetragonal phase zirconia. The presence of water on the surface of these mesoporous catalysts contributes to their activity as has been recently reported with the conventional catalysts. Catalyst deactivation on sulfated zirconia is rapid at 250°C. Two regimes of deactivation were observed over conventional sulfated zirconia at varying partial pressures of n-butane.; A dual active site kinetic model with deactivation is proposed to quantitatively describe the deactivation process of n-butane isomerization. The model consists of two active sites decaying at different rates, consistent with reaction pathways suggested in the literature. A single active site model is inadequate in explaining the deactivation trends observed experimentally.; The mesoporous catalyst is also active for the isomerization of n-pentane. Addition of platinum metal decreased the rate of deactivation but suppressed the high initial activity observed on the unpromoted catalysts. Surface areas decreased on the mesoporous catalyst with increased sulfur loading. The mesoporous catalyst with 3wt% sulfur loading and platinum addition performed after calcination is the most active for n-pentane isomerization.