Fig. 5: ²⁹Si MAS-NMR spectra of HFAU(40-2.6) and reaction pathways.

a The fourfold increase in the Q⁴(2Al) and Q⁴(3Al) bands indicates an increasing amount of adjacent Brønsted acid sites when decreasing the Si/Al ratio. b G4 reaction pathways of catechol dehydration at unimolecular and acid-catalyzed conditions.