Studies on sulphated zirconia: synthesis, physico-chemical characterisation and n-butane isomerisation activity Original Research Article

A series of sulphated zirconia samples having different weight percentages of sulphate were synthesised by wetness impregnation of zirconium hydroxide with an aqueous solution of (NH4)2S2O8. The structural, surface and catalytic properties of these samples, calcined at different temperatures were investigated using XRD, BET, FTIR, UV–VIS diffused reflectance studies (DRS), photoacoustic measurements, adsorption of pyridine from non-aqueous solvent, surface hydrophilicity and n-butane isomerisation reaction. XRD and UV–VIS DRS revealed that sulphate stabilises the tetragonal phase of zirconia by controlling embryo growth. The FTIR spectral patterns supported the presence of two different types of sulphate, which were bidentately co-ordinated to zirconium matrix. Both Brönsted and Lewis acidity were increased with increase in nominal sulphate loading. Drastic changes were observed in 15 wt.% sulphated sample, which exhibited quite high values of Brönsted and Lewis acidity but very low butane isomerisation activity. The effect of pre-treatment temperature, and nominal sulphate loading on n-butane conversion suggested involvement of a Lewis–Brönsted synergy in butane isomerisation reaction.