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

The effect of platinum concentration on tungsten oxide-promoted zirconia ov er 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-hexa ne 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 increa se for platinum concentrations above 0.05% because of higher hydrogen avail ability at the surface, measured as a function of the methylcyclopentane/C- 6 isomers ratio; Further increments in platinum concentration do not produc e important modifications in catalytic activity or hydrogen availability. M echanical mixtures of Pt/SiO2 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 El sevier Science B.V. All rights reserved.