In situ study of alkane conversion on Pt-loaded acidic zeolites

The hydroisomerization of hexane on platinum-loaded acidic zeolites was studied with positron emission profiling (PEP), a tracer imaging technique based on the same principle as positron emission tomography. The unique character of PEP enables the determination of reaction parameters under in situ reaction conditions that are difficult to obtain via ex situ techniques. A numerical model, including the effects of adsorption, diffusion, and reaction, was used to fit the measured concentration profiles. Preexponential factors and activation energies for some of the elementary proton-activated reaction steps of the bifunctional reaction mechanism have been determined in different transient experiments for a variety of platinum-loaded acidic zeolites. An activation energy for dehydrogenation of 98 kJ/mol was found, in which the heat of adsorption appeared to be included. The heat of adsorption was found to be 61 kJ/mol. An upper value for the deprotonation energy of 100 kJ/mol was determined. This is in agreem...