N-Hexane Reactions on EUROPT-1 at Different Hydrogen Pressures: The Possibility of Calculating Kinetic Parameters

Abstract

Skeletal reactions of n-hexane on 6.3% Pt/SiO2 (EUROPT-1) have been studied as a function of hydrogen pressure between 483 and 633 K. Turnover frequencies were calculated for the overall reaction as well as for individual processes, i.e., hydrogenolysis, isomerization, C5-cyclization, and aromatization as well as dehydrogenation to hexenes. Curves with a maximum were observed for the conversion as a function of hydrogen pressure. Arrhenius plots could be calculated for constant hydrogen pressures as well as for maximum rates. The former lines “bend down” at higher temperatures. This may explain the different values determined in different experimental setups. Different straight Arrhenius lines were determined in the negative and in the positive hydrogen order range. We regard activation energies calculated at constant hydrogen pressures as “apparent” while those computed at the maximum rates may approximate “true” values. The apparent activation energies show compensation effect and give different compensation lines in the range of positive and negative hydrogen orders. In the case of bent Arrhenius plots, the computation resulted in virtual isokinetic parameters. Arrhenius parameters and compensation phenomena were determined for individual reactions, too. These results are in a good agreement with the mechanism suggested earlier for each reaction.