Coke deposition on platinum promoted WOx-ZrO2 during n-hexane isomerization

Platinum on tungsten oxide promoted zirconia catalysts were prepared by cal cining the zirconium hydroxide impregnated with tungsten species at differe nt temperatures before platinum addition. Both the amount and nature of cok e deposited on these catalysts during the R-hexane isomerization were studi ed. It was found that the amount of coke formed is small (<0.5%) over all s amples. A similar type of coke was produced on catalysts calcined above 600 degrees C, its amount showing a relationship with the catalytic activity. The higher the specific rate, the larger the carbon content. A more hydroge nated and aliphatic coke was observed over the catalyst calcined at 500 deg rees C, the difference being related to the properties of WOx-ZrO2 calcined at this temperature. The material calcined at 700 degrees C before platinu m addition reached the largest catalytic activity and a similar carbon cont ent referred to the surface area than materials calcined at higher temperat ures. Coke can be burnt out at 500 degrees C. (C) 1999 Elsevier Science B.V . All rights reserved.