Comparative study of aerogels nanostructured catalysts: Ni/ZrO₂–SO₄ ²⁻ and Ni/ZrO₂–Al₂O₃–SO₄ ²⁻

Abstract

A series of Ni/ZrO₂–SO₄ ²⁻ and Ni/ZrO₂–Al₂O₃–SO₄ ²⁻ catalysts were prepared in one step by the sol–gel method and dried in hypercritical conditions of the solvent. The characteristic properties of those solids were investigated using many techniques: the XRD, the physisorption of N₂, the IR, the UV–visible, and the X-ray photoelectron spectroscopy (XPS). Textural analysis reveals the mesoporosity of all the aerogel catalysts. Moreover, the addition of alumina to nickel sulfated zirconia at high calcination temperature increased twice the specific surface area, from 72 to 158 m²/g. XRD patterns show that nickel-promoted sulfated zirconia calcined at different temperature develops the tetragonal and the monoclinic ZrO₂ phase, whereas the nickel sulfated zirconia alumina exhibits only the ZrO₂ tetragonal phase. The addition of aluminum to nickel sulfated zirconia induces significant changes in symmetry of nickel by the migration of Ni ions from octahedral to tetrahedral coordination. XPS spectroscopy shows that the nickel in Ni/ZrO₂–SO₄ ²⁻ catalysts is more reducible than those in Ni/ZrO₂–Al₂O₃–SO₄ ²⁻. Nickel sulfated zirconia catalyst exhibits higher activity than nickel sulfated zirconia alumina, in the n-hexane isomerization reaction.