Effect of the doping agent nature on the characteristic and catalytic properties of aerogel zirconia catalysts doped with sulfate groups or heteropolytungstic acid

• We focused on the selectivity and the octane number of each isomers.
• Aerogel zirconia solids issued from sulfurs or HPW differ noticeably in properties.
• Sulfates as dopant do not allow the control of selectivity towards valuable isomers.
• HPW is promising to obtain more valuable isomers at 220 °C.

Zirconia catalysts doped with sulfates or heteropolytungstic acid (HPW) prepared by sol–gel method and dried in supercritical conditions of solvent have been evaluated in n-hexane isomerization in the temperature range 150–220 °C. Using HPW as dopant, the obtained catalyst is active at 220 °C and selective towards isomers having higher Individual Octane Number, i.e., 2,2-DMB and 2,3-DMB compared with using sulfates as dopant. Based on N2-physisorption, XRD, SEM and TEM analyses, low specific area, particular morphology of grains and the lack of tetragonal ZrO2 particles reduce the adsorption of n-hexane reactant and led to inefficient catalyst throughout the temperature range 150–200 °C. The catalyst doped with sulfur deactivates at T > 200 °C since agglomerates of zirconia particles (TEM and SEM results) favor the coke formation. Using HPW, agglomerates of W oxide as well as phosphate groups (revealed by TGA, FTIR, EDX and UV/visible DRS) favor the formation of more valuable isomers at 220 °C.

Figure optionsDownload as PowerPoint slideEffect of the doping agent nature on the characteristic and catalytic properties of aerogel zirconia catalysts doped with sulfate groups or heteropolytungstic acid