Role of Catalyst Acidity in Glucose Conversion over Sn-Al-ß Zeolite as Studied by Solid-state NMR

A series of ss zeolite catalysts with different acidic properties were prepared. The acidity of these catalysts was characterized by solid-state nuclear magnetic resonance (NMR) probe molecule technique. These catalysts were tested for the conversion of glucose to methyl levulinate. P-31 NMR of trimethyl phosphine adsorbed on Sn-Al-ss zeolite showed that the introduction of framework Sn and Al atoms resulted in both Bronsted and Lewis acidity. Three Bronsted acid sites with different acidic strength were distinguished by C-13 NMR of 2-C-13-acetone probe molecule, with one being close tosuper acid, which is most likely generated by the synergistic effect between the spatially adjacent Bronsted and Lewis acid sites. The catalytic reaction of glucose to methyl levulinate showed that Sn-Al-ss was superior in catalytic activity and selectivity to methyl levulinate as compared to Sn-ss containing only Lewis acid sites, Al-ss containing only Bronsted acid sites and the mixed sample of Sn-ss and Al-ss. This can be accounted by the synergy of Bronsted and Lewis acid sites and stronger Bronsted acidity of Sn-Al-ss.

Automated summary

A series of ss zeolite catalysts with different acidic properties were prepared and characterized by solid-state nuclear magnetic resonance (NMR) probe molecule technique. The introduction of framework Sn and Al atoms resulted in both Bronsted and Lewis acidity, with a synergistic effect between the spatially adjacent Bronsted and Lewis acid sites. Sn-Al-ss catalyst showed superior catalytic activity and selectivity to methyl levulinate compared to other samples, attributed to the synergy of Bronsted and Lewis acid sites and stronger Bronsted acidity of Sn-Al-ss.