Journal
CATALYSIS SCIENCE & TECHNOLOGY
Volume 10, Issue 24, Pages 8254-8264Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d0cy01662d
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Funding
- Government of Romania, Ministry of Research and Innovation [PN-III-P1-1.1-PD-2016-1054, 29/2018]
- OP VVV Excellent Research Teams project [CZ.02.1.01/0.0/0.0/15_003/0000417- CUCAM]
- Czech Science Foundation project EXPRO [19-27551X]
- Czech Science Foundation [20-12099S, 19-21534S]
- Grant Agency of Charles University project [1398119]
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Isomorphic substitution of silicon for germanium affords germanosilicate zeolites with weak acid centers capable of catalyzing key reactions such as Baeyer-Villiger oxidation of ketones and etherification of levulinic acid. Herein, we show for the first time that UTL (Si/Ge = 4.2) and IWW (Si/Ge = 7.2) germanosilicate zeolites are active and selective catalysts of polyol (e.g., ethylene glycol, glycerol and 1,4 butanediol) ketalization to dioxolanes. Large-pore IWW outperformed the extra-large-pore UTL zeolite in the ketalization of polyols, thus indicating diffusion limitations in bulky platelet-like UTL crystals. FTIR spectroscopy of adsorbed pyridine revealed the Lewis acidity of the UTL zeolite, whereas the more active IWW catalyst was characterized by water-induced Bronsted acidity. Increasing the activation temperature (200-450 degrees C) reduced the concentration of Bronsted acid centers in the IWW germanosilicate (i.e., 0.16; 0.07 and 0.05 mmol g(-1) for T-act = 200, 300 and 450 degrees C, respectively) but increased the number of Lewis acid sites in both zeolites. Under optimized reaction conditions (e.g., acetone/glycerol = 25, T-act = 300 degrees C), almost total transformation of glycerol into solketal was achieved within 3 h of reaction time over the IWW zeolite at room temperature (>99% yield of the target product). The results from the present study clearly show that weak acid centers of germanosilicate zeolites can serve as active sites in ketalization reactions.
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