n-hexane reactions on EUROPT-1 at different hydrogen pressures: The possibility of calculating kinetic parameters

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 frequen cies were calculated for the overall reaction as well as for individual pro cesses, i.e., hydrogenolysis, isomerization, Cs-cyclization, and aromatizat ion as well as dehydrogenation to hexenes. Curves with a maximum were obser ved 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 explai n the different values determined in different experimental setups. Differe nt straight Arrhenius lines were determined in the negative and in the posi tive hydrogen order range. We regard activation energies calculated at cons tant hydrogen pressures as "apparent" while those computed at the maximum r ates may approximate "true" values. The apparent activation energies show c ompensation effect and give different compensation lines in the range of po sitive and negative hydrogen orders. In the case of bent Arrhenius plots, t he computation resulted in virtual isokinetic parameters. Arrhenius paramet ers and compensation phenomena were determined for individual reactions, to o. These results are in a good agreement with the mechanism suggested earli er for each reaction. (C) 1999 Academic Press.