The nature of coke on platinum over tungsten oxide promoted zirconia during n-hexane isomerization

Abstract

ABSTRACT The nature of coke, which is deposited during n-hexane isomerization on platinum over tungsten oxide promoted zirconia and prepared by using two different platinum precursors and different calcination temperatures after Pt addition, as well as different Pt concentrations for one of the precursors, has been studied. One of the catalysts was used under different operational conditions. The presence of platinum decreases significantly the maximum temperature needed to burn off the coke. In the absence of hydrogen, the amount of coke on the Pt containing catalysts is large, but some hydrogen provided by coke or by a very small amount of olefins formed avoids an increase in the temperature of the coke burnt off. The platinum precursor does not affect the amount and nature of coke, but the temperature of calcination after platinum addition plays a more important role. Temperatures of operation above 225 °C using a Pt containing catalyst or the absence of Pt, are the most important factors producing a coke more difficult to be burnt-an important feature when regeneration procedures must be carried out.