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

Author(s)

Araujo Silva, Domingos S. ^[1] ; Castelblanco, William N. ^[1] ; Piva, Diogenes Honorato ^[1] ; de Macedo, Vinicius ^[1] ; Carvalho, Kele T. G. ^[1] ; Urquieta-Gonzalez, Ernesto A. ^[1]

Affiliation

^[1] Univ Fed Sao Carlos, Res Ctr Adv Mat & Energy, C Postal 676, BR-13565905 Sao Carlos, SP - Brazil

• Document type: Journal article
• Source: MOLECULAR CATALYSIS; v. 492, AUG 2020.
• Web of Science Citations: 0

Abstract

Diffusion and acidity of molecules are key parameters in organic synthesis; therefore, highly stable mesoporous HZSM-5 zeolites with ratios of Bronsted (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, N-2 physisorption, NH3-TPD, DRIFTS, and Si-29-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 C-B/C-L 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 C-B/C-L 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. (AU)

• FAPESP's process: 14/50249-8 - Green chemistry: sustainable synthetic methods employing benign solvents, safer reagents, and bio-renewable feedstock
• Grantee: Arlene Gonçalves Corrêa
• Support Opportunities: Research Grants - Research Centers in Engineering Program