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Tuning the Brønsted and Lewis acid nature in HZSM-5 zeolites by the generation of intracrystalline mesoporosity – Catalytic behavior for the acylation of anisole

Molecular Catalysis Journal

Diffusion and acidity of molecules are key parameters in organic synthesis; therefore, highly stable mesoporous HZSM-5 zeolites with ratios of Brønsted (CB) to Lewis (CL) acid sites tuned by alkaline desilication were employed for Friedel–Crafts acylation of anisole with acetic anhydride. Controlled zeolite desilication (Si/Al = 12 and 23) proceeded by varying the NaOH concentration, temperature, and treatment time. SEM/EDS, XRD, N2 physisorption, NH3-TPD, DRIFTS, and 29Si-MAS-NMR data were used to correlate the generated intracrystalline mesoporosity with the new textural, acidic, and catalytic properties. It was evidenced that desilication allowed the CB/CL ratio to vary from 21 to 2.3. During anisole acylation, the specific activity to 4-methoxyacetophenone (4-MAP), on a desilicated zeolite that preserved most of the original microstructure, markedly increased with increasing mesoporosity, even a decrease of the CB/CL ratio had occurred. The strong changes in the acid nature and textural properties did not change the anisole acylation acid mechanism and improved the internal diffusion of reactants and 4-MAP to or from the active sites, respectively. Thus, appropriate levels of mesoporosity with consequent acidity changes may be designed through controlled zeolite desilication, with the resultant hierarchical zeolite capable of being applied as a catalyst to a particular organic reaction mechanism.

For details: Tuning the Brønsted and Lewis acid nature in HZSM-5 zeolites by the generation of intracrystalline mesoporosity – Catalytic behavior for the acylation of anisole

Domingos S. Araújo Silva, William N. Castelblanco, Diógenes Honorato Piva, Vinícius de Macedo, Kele T.G. Carvalho, Ernesto A. Urquieta-González

Research Center on Advanced Materials and Energy, São Carlos Federal University, C. Postal 676, CEP 13565-905, São Carlos, SP, Brazil

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Molecular Catalysis Journal
https://doi.org/10.1016/j.mcat.2020.111026

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July 1, 2020