posted on 2024-02-23, 12:33authored byL. Ouayloul, I. Agirrezabal-Telleria, P. L. Arias, F. Dumeignil, M. El Doukkali
Solid-acid ZSM-5 catalysts stand
out as highly reactive
for ethanol
dehydration, but the selective production of ethylene at low temperatures,
however, is still a challenge. Herein, two ZSM-5 zeolites with a distinct
Si/Al ratio have been modified with Ce, La, or P species or treated
with H2O or NH3 to get a better understanding
on the contribution of acid sites to the ethanol-to-ethylene catalysis.
The doping of ZSM-5 affects both the number and strength of acid sites,
of which the Ce content inversely increases the population of weak
acid sites (WAS). Atomically dispersed oxygen vacancy-rich CeOx synergistically contribute to the dissociation
of H2O during the synthesis of Al-rich ZSM-5 to modify
the local Al environment by forming new Al–OH bonds, acting
as WAS. This significantly enhances the conversion of ethanol into
intermediates and ultimately into ethylene (selectivity up to 92%).
Further poisoning of strong acid sites (SAS) by in situ NH3-titration confirms that ethanol-to-ethylene catalysis at low temperatures
occurs mostly over WAS, while the contribution of SAS is minor. The
underpinning insights can serve as a basis for further developments
in the combination of other multivalence species with ex situ water
treatments or in situ cofeeding to design robust catalysts that are
able to efficiently dehydrate bioethanol into ethylene at low temperatures.