Cellulose conversion to ethylene glycol by tungsten oxide-based catalysts

Abstract

The conversion of cellulose into ethylene glycol remains a significant challenge in the biobased domain. Here we explored the activity of various bulk and mesoporous (doped) tungsten oxides in combination with carbon-supported ruthenium for obtaining ethylene glycol from cellulose. Tungstite and sub-stoichiometric tungsten oxides are more active and selective than monoclinic WO3. Doping tungstite with early transition metals enhanced the rate of cellulose depolymerization to glucose through a higher Brønsted acidity, although this did not improve the overall performance as the higher acidity resulted in a higher rate of humin formation. The increased acidity of mesoporous sub-stoichiometric tungsten oxide compared to tungstite had a similar adverse effect. Doping this material with niobium improved ethylene glycol selectivity at similar conversion. Kinetic studies showed that the majority of ethylene glycol is produced in the first hour for three optimized catalysts, with undoped bulk tungstite being the most efficient catalytic material. Impregnation of these materials with ruthenium instead of using carbon-supported ruthenium as a co-catalyst was most beneficial for tungstite, as it showed improved ethylene glycol selectivity and lower polyol yields after 1 h of reaction time.