Brønsted-dominated dual-acid synergy enables efficient room-temperature biomass acetalization over fibrous mesochanneled aluminosilicates

Acetalization of biomass-derived aldehydes and ketones catalyzed by solid acids represents a promising strategy for producing sustained-release fragrance carriers. Nevertheless, conventional microporous zeolites are plagued by mass transfer constraints and undesired side-reactions, particularly with bulky substrates. Adding to this complexity, the synergistic interplay between coexisting Lewis and Brønsted acid sites remains poorly understood. Here, we design a new-type of protonated fibrous mesochanneled aluminosilicates (H-Fibr-MAS) via in-situ Al incorporation, featuring open mesochannels and balanced Brønsted (Si-OH-Al) and Lewis (non-framework Al) acid sites. H-Fibr-MAS outperforms Al post-loading analogs (AlOx/Fibr-Silica), commercially protonated microporous zeolites and typical acidic metal oxides in biomass acetalization at room temperature (25 °C). Combining structure-activity correlations, site-poisoning experiments, and in-situ difference Fourier transformed infrared spectroscopy (FTIR), we unveil a Brønsted-dominated Lewis-Brønsted acid synergistic mechanism: Lewis acid sites selectively activate the carbonyl group of furfural, while Brønsted acid sites (especially medium-to-strong sites) facilitate the hemiacetal dehydration, the latter step being previously overlooked but exactly decisive in this dual-acid synergy. Our work establishes acid-site engineering and dual-acid synergy as key principles for designing efficient solid acids in biomass valorization.