Influence of the sulfate content on the activity of Pt containing sulfated zirconia Original Research Article

Sulfated zirconias (SZ) with different sulfur content were prepared by controlled impregnation of zirconium hydroxide with corresponding amounts of 1N H2SO4. After drying the samples were impregnated with 2.5 wt% Pt. All samples exhibited pure tetragonal structure except one with the lowest sulfur content where small amounts of the monoclinic ZrO2 phase were detected. Temperature-programmed desorption of ammonia and pyridine adsorption followed by IR measurements were carried out in order to determine the nature of acid sites. It was found that the concentration of Brønsted acid sites depends on the concentration of surface sulfates. On samples with more than half of a monolayer sulfates Brønsted acid sites were detected. On SZ with 46% of a monolayer sulfates and on a sample, which was inactive after regeneration in an inert atmosphere only Lewis acid sites were observed.The n-heptane conversion was studied at 473 K and atmospheric pressure. SZ catalysts were only active when Brønsted acid sites were present on the surface. The activity increased with increasing sulfate content whereas the isomerization selectivity decreased.