The
adsorption and diffusion are key parameters for the catalytic
conversions of ethylene to hydrocarbons. Using microcrystals of beta
zeolites and the reversed-flow inverse gas chromatography technique,
a new approach is developed for the catalytic characterization of
pristine crystals. On the basis of the monitoring of the dynamic concentration
in a time-resolved way, this method allows one to follow the surface
coverage and adsorption energies among other physicochemical criteria.
Pristine crystals were synthesized to rule out the effect of surface
defects. The impact of porosity and acidity was studied by ethylene
adsorption over porous, nonporous, and acid materials. The acidity
of the mother zeolite (acid and porous) was decreased by retro-exchanges
and partial cokage. The modification of the ethylene sorption due
to the Brønsted acidity was then highlighted. The local surface
coverage was not affected by the presence of porosity, while a second
adsorption phase of the ethylene was induced by the modification of
the acidity. Moreover, a relation between the amount of Brønsted
acidity and the ethylene lateral interactions measured by RF-IGC was
evidenced.