Sol-gel preparation of highly active sulfated zirconia supported by alumina catalysts

A series of sulfated mixed oxides of alumina and zirconia having a relative composition of 5% and 10% of ZrO2 was prepared by means of sol-gel methods using zirconium propoxide or zirconium acetylacetone as precursor. The characterization of the physicochemical properties was carried out using Al-27 NMR, XRD, N-2 adsorption at 77 K, thermogravimetry, FTIR analysis of adsorbed pyridine, Al-27 NMR-MAS and XPS. The catalytic properties were studied by means of isomerization of n-hexane at 250degreesC. Results obtained allowed to propose that the use of Zr(acac)(4) as a zirconium precursor leads to a better retention of sulfate species which seems to form polymeric superficial sites. The symmetry of aluminium undergo an increase from tetrahedral to octahedral coordination and Zirconium atoms seems to be located in the second coordination sphere of Al. XRD analysis indicated an amorphous structure of obtained solids calcined at 650degreesC. The sulfated solids presented both Lewis and Bronsted acidic sites. Catalytic results showed that both activity and selectivity towards isomerization products were better using Zr (acac)(4) as precursor. Furthermore, the increase of the Zr loading affected considerably the catalytic properties of sulfated zirconia supported by alumina.