Promoting aromatic C-H activation through reactive Brønsted 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-d₆. With increasing Al content of ASAs, the exchange rate increased, whereas the activation energy (E_a) slightly decreased due to the enhanced Brønsted 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.
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