Influence of Pt concentration on tungsten oxide-promoted zirconia during n-hexane isomerization

The effect of platinum concentration on tungsten oxide-promoted zirconia over the catalytic activity for n-hexane isomerization was studied. Catalysts were prepared by impregnation of tungsten oxide-promoted zirconia reaching up tb 1.50% platinum, followed by calcination at 500 degrees C. The n-hexane reaction was studied at 200 degrees C, 5.9 bar, WHSV 4 and H(2): n-hexane (molar) ratio 7. It was found that catalytic activity and stability increase for platinum concentrations above 0.05% because of higher hydrogen availability at the surface, measured as a function of the methylcyclopentane/C(6) isomers ratio; Further increments in platinum concentration do not produce important modifications in catalytic activity or hydrogen availability. Mechanical mixtures of Pt/SiO(2) and tungsten oxide-promoted zirconia present a lower conversion than platinum over tungsten oxide-promoted zirconia due to the larger distance between the acid and metallic functions. (C) 2000 Elsevier Science B.V. All rights reserved.