Promoting Aromatic C-H Activation through Reactive Bronsted Acid-Base Pairs on Penta-Coordinated Al-Enriched Amorphous Silica-Alumina

The surface acidity and local coordination environment of zeolites and amorphous silica-aluminas (ASAs) can promote acid-catalyzed C-H activation in many important hydrocarbon conversion reactions. Acid sites generated by penta-coordinated Al species (Al-v) can lead to enhanced acidity and changes in the surface coordination. We evaluated the potential of flame-derived ASAs with enriched Al-v for C-H activation using hydrogen/deuterium (H/D) exchange with benzene-d(6). With increasing AI content of ASAs, the exchange rate increased, whereas the activation energy (E-a) slightly decreased due to the enhanced Bronsted acidity. The ASAs exhibited significantly higher exchange rates and lower E-a values than the sol-gel-derived ASAs and zeolite H-ZSM-5. The superior activity is attributed to the fact that more oxygen coordinated with Al(v )species on flame-made ASAs, which can act as acceptors for D+, enhancing the deuterium displacement. These findings could offer a valuable alternative strategy for tailoring high-performance solid acids to promote hydrocarbon conversion reactions.

Automated summary

This study found that flame-derived amorphous silica-aluminas exhibit higher activity in hydrocarbon conversion reactions due to their enhanced surface acidity and local coordination environment. The flame-derived ASAs showed higher exchange rates and lower activation energy, attributed to the increased oxygen coordination with Al species, which enhances the ability to accept D+.