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

Zichun Wang; Yijiao Jiang; Alfons Baiker; Michael Hunger; Jun Huang

doi:10.1021/acs.jpclett.1c03489

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

J Phys Chem Lett. 2022 Jan 20;13(2):486-491. doi: 10.1021/acs.jpclett.1c03489. Epub 2022 Jan 10.

Authors

Zichun Wang¹, Yijiao Jiang², Alfons Baiker³, Michael Hunger⁴, Jun Huang¹

Affiliations

¹ Laboratory for Catalysis Engineering, School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, New South Wales 2006, Australia.
² ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia.
³ Institute for Chemical and Bioengineering, Department of Chemistry and Applied Bioscience, ETH Zürich, HCI, CH-8093 Zürich, Switzerland.
⁴ Institute of Chemical Technology, University of Stuttgart, D-70550 Stuttgart, Germany.

PMID: 35001618
DOI: 10.1021/acs.jpclett.1c03489

Abstract

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.