Productive sugar isomerization with highly active Sn in dealuminated β zeolites

A water-tolerant Lewis acid catalyst was synthesized by grafting Sn-iv in isopropanol under reflux onto dealuminated zeolites with the BEA (beta) topology. This synthesis method allows the production of highly active Sn beta-type catalysts without the need for long hydrothermal syntheses or hydrogen fluoride, while using cheap Sn-precursors, industrially available beta zeolites and standard catalyst synthesis unit operations. Extensive characterization of the best catalyst shows highly dispersed Sn in the zeolite matrix (XRD, (SI)-S-29 MAS NMR and H-1 MAS NMR) without the formation of SnO2 (XRD and UV-Vis). The catalyst was tested for the model isomerization of sugars such as glucose to fructose. The catalytic activity proved to be purely heterogeneous and the catalyst was recycled and reused without significant loss in activity. Isomerization productivities above 4 kg product per kg of catalyst per hour are reported with appreciably low Sn loadings, corresponding to exceptionally high turnover frequencies, viz. 500 cycles per Sn per hour at 110 degrees C, which surpass the activity per Sn of the original hydrothermally synthesized Sn beta.