Acidic properties of mesoporous nanoparticles sulfated 75%TiO2-25%ZrO2 mixed oxide; performance in the catalytic dehydration of isopropanol to propene

The sulfated SO4/TiO2-ZrO2 (75:25 mol%) mixed oxide (STZ) was investigated for the catalytic dehydration of isopropanol. The mixed oxides were synthesized by the sol-gel method using titanium (IV) isopropoxide and zirconium (IV) n-propoxide as precursors. The sulfated mixed oxide was synthesized by impregnation of the corresponding hydroxide with H2SO4. TGA-DTA and elemental analysis of the sulfated sample showed no decomposition of sulfates after heating to temperatures below 550°C. Nanomaterials were revealed by SEM for both unmodified and sulfated titania-zirconia. XRD showed that both pure and sulfated TiO2-ZrO2 are virtually amorphous. A monomodal mesoporous structure was identified for both samples, with high specific surface areas reaching 350 and 250 m2 g-1, respectively, for the pure and sulfated materials. Adsorption of 2,6-dimethylpyridine (DMP) followed by FTIR showed that sulfate ions enhanced the density of Brønsted acid sites and generated very strong Lewis acid sites, with a strength comparable to that of highly dehydroxylated commercial g-Al2O3, generally taken as a reference for its strong Lewis acidity. The synergistic effect between the high density of Brønsted acid sites and the strength of the Lewis acid sites makes the stable sulfated TiO2-ZrO2 mixed oxide highly active and selective towards the isopropanol dehydration reaction to propene