Alternatives for a better performance of Pt in SO2−4–ZrO2 catalysts for n-octane hydroisomerization-cracking. Selective adsorption of Pt over composites of SO2−4–ZrO2 mixed or supported onto Al2O3 and SiO2 Original Research Article

The addition of Pt over various pure and heterogeneous supports containing zirconia promoted by the SO2−4 oxoanion was studied. The supports used were: (i) pure SO2−4–ZrO2; (ii) mechanical mixtures of γ-Al2O3 or SiO2 with SO2−4–ZrO2; and (iii) SO2−4–ZrO2 supported onto γ-Al2O3 or SiO2. Variations in the particle size of SO2−4–ZrO2 and the technique of Pt deposition were performed in order to meet two seemingly contradictory objectives: (i) avoid a harmful physicochemical association of Pt and the SO2−4 containing acid function; and (ii) reduce the mean free path between them. For the alumina- or silica-containing catalysts, a selective adsorption technique – based on electrostatic repulsion/attraction between different Pt precursors and the supports – was employed in order to avoid the anchorage of Pt onto sulfated zirconia during impregnation. Supported sulfate–zirconia was synthesized as a means of obtaining highly dispersed small particles of the acidic function. A new method of sulfation with a previous reducing treatment in hydrogen of the sintered and crystalline supported zirconia was found to be superior to the common technique of sulfation of the amorphous dispersed hydroxide.