Isomerization of n-alkanes on Pt/WO3-SO4/ZrO2 systems

The role of the electronic state of Pt and acidic properties of anion-promoted support in n-alkane isomerization on Pt-containing sulfate- and tungstate-promoted zirconia (Pt/SZR and Pt/WZR) was studied. The addition of Pt with further oxidation and mild reduction is found to enhance the catalytic activity in n-hexane isomerization 10 times compared with metal-free system. The mechanism of the action of the pretreatment steps is proposed. Effect of the calcination temperature on the catalytic activity in n-alkane isomerization and physico-chemical properties of the catalysts is also evaluated. The catalytic activity of Pt promoted combined sulfated-tungstated zirconia (Pt/SWZR) catalysts in n-hexane and n-pentane isomerization decreases in the following order (the calcination temperature is shown in parentheses): Pt/SZR (625 degreesC) > Pt/WSZR (625 degreesC) > Pt/WSZR (800 degreesC) approximate to Pt/WZR (800 degreesC) The properties of WZR (800 degreesC) and SWZR (800 degreesC) are connected with the surface WO4 groups. The presence of sulfate species in Pt/SZR (625 degreesC) and Pt/WSZR (625 degreesC) is responsible for the strong acidic properties of these catalysts. The performance of classical sulfated and tungstated catalysts is slightly improved by the combination of anions. (C) 2002 Elsevier Science B.V. All rights reserved.