Unraveling the active states of WO3-based catalysts in the selective conversion of cellulose to glycols

Tungsten-based catalysts, including crystalline WO3 and H2WO4, have been reported to be efficient for the selective cleavage of C-C bonds of sugar intermediates involved in the conversion of cellulose to ethylene glycol and propylene glycol in combination with hydrogenation catalysts under H2 atmosphere. However, there is still nota consensus on the actual states of these catalysts during the reaction. Herein, we demonstrate that both WO3 and H2WO4 tended to undergo reduction to hydrogen tungsten bronze (HxWO3) species in the cellulose reaction, consisting of H0.23WO3 and H0.33WO3, which were then re-oxidized to WO3 upon exposure to ambient air after the reaction. Both WO3 and HxWO3 were insoluble in water and acted as the heterogeneous catalysts in the cellulose reaction, as further validated by the strong dependence of the catalytic activity of WO3 on its crystallite size and surface area. Such identification of the heterogeneous HxWO3 species, albeit exemplified here only from the in situ reduction of WO3 and H2WO4 in the cellulose reaction, unravels the active state of the tungsten-based catalysts under reductive reaction conditions. Published by Elsevier B.V. All rights reserved.

Automated summary

Tungsten-based catalysts, including WO3 and H2WO4, can selectively cleave C-C bonds in sugar intermediates during the conversion of cellulose to ethylene glycol and propylene glycol. The catalysts undergo reduction to HxWO3 species during the reaction, which act as heterogeneous catalysts and are re-oxidized to WO3 upon exposure to ambient air after the reaction. The activity of WO3 is strongly dependent on its crystallite size and surface area.