Isomerization of n-hexane on the Pt-promoted Keggin and Dawson tungstophosphoric heteropoly acids supported on zirconia

Abstract

The activity of the Pt-promoted systems prepared on the basis of Keggin H 3PW 12O 40 (HPW) and H 3PW 11Zr (HPW 11Zr), and Dawson H 6P 2W 18O 62 (HP 2W 18) and H 6P 2W 21O 71 (HP 2W 21) heteropoly acids supported on zirconia in the isomerization of n-hexane was studied. The Pt/HPW/ZrO 2 catalytic system shows high activity in n-hexane isomerization. The yield of isohexanes was close to 80% and the selectivity was 96–98% at 190 °C. The DTA and FTIR spectroscopic studies allowed us that partially distorted grafted Keggin ions are responsible for the catalytic activity. However, these species cannot be formed by dispersion of HP 2W n and HPW 11Zr heteropoly acids because of their insufficient stability. The support of these systems on ZrO 2 is accompanied by significant structural transformations. The Pt/HP 2W n /ZrO 2 or HPW 11Zr/ZrO 2 catalytic systems shows the best performance (yield is close to 80%) at higher temperatures (30–40 °C) than Pt/HPW/ZrO 2. However, these systems show higher selectivity due to lower density of active sites and inhibition of bimolecular alkylation–cracking side reactions.