Effect of calcination temperature of La- and Ni-promoted S 2 O 8 2– /ZrO 2 –Al 2 O3 catalysts on the isomerisation of n -pentane

A series of bimetal La- and Ni-promoted S₂O₈^2–/ZrO₂–Al₂O₃ (SZA) catalysts were prepared at different calcination temperatures. The effect of calcination temperature on the characteristics and performance of La-Ni-S₂O₈^2–/ZrO₂–Al₂O₃ (La-Ni-SZA) catalysts towards the n-pentane isomerisation reaction was determined. In order to relate the catalytic activity to their physical, chemical and textural features, the catalysts were characterised by various techniques including X-ray powder diffraction, thermogravimetric-differential thermal analysis, Fourier transform infrared spectroscopy (FTIR), FTIR spectra of adsorbed pyridine and BET specific surface area and H₂ temperature-programmed reduction analyses. The results showed that tetragonal ZrO₂ was the dominant phase in the calcination temperature range of 600–700 °C. The change of textural features of the catalysts results from transformation of the ZrO₂ crystal phase and the collapse of the partial pore structure occurs at the high calcination temperature of 700 °C. The sulfur could be lost at calcination temperatures > 660 °C. The total acidity of the catalysts at a desorption temperature of 350 °C decreases in the order: La-Ni-SZA-650 > La-Ni-SZA-600 > La-Ni-SZA-700 > La-Ni-SZA-550. The La-Ni-SZA catalyst calcined at 650 °C had more tetragonal phase ZrO₂, higher acidity, higher sulfur content, a larger BET surface area and exhibited the best catalytic performance, with the isopentane yield reaching a maximum 66.5% at a lower reaction temperature of 150 °C, with a selectivity to isopentane of 98.5%.