Production of Hexane-1,2,5,6-tetrol from Biorenewable Levoglucosanol over Pt-WO_x/TiO₂

We have investigated the synthesis of hexane-1,2,5,6-tetrol (hereafter "tetrol") from aqueous solutions of biomass-derived levoglucosanol (hereafter "Lgol") using a (10 wt %)Pt-(10 wt %)WOx/TiO2 catalyst in both batch and continuous flow reactors. The tetrol selectivity was over 90% with Lgol feed concentrations of 10-30 wt %. Most of the Lgol feed stereochemistry was preserved (notably 91%), with threo-Lgol (hereafter "t-Lgol") and erythro-Lgol (hereafter "e-Lgol") converting to (S,S)-tetrol and (S,R)-tetrol, respectively. The rate of Lgol conversion was found to be first-order in the Lgol concentration, suggesting that the catalyst surface is not saturated with Lgol. The measured reaction order for H2 was zero, which is consistent with either a mechanism involving acid-catalyzed irreversible C-O bond cleavage of Lgol followed by metal-catalyzed hydrogenation of reactive intermediates or one where all of the metal sites are saturated with H2. When the reaction was run in a continuous flow reactor, the catalyst exhibited deactivation with increasing time-on-stream but was found partially regenerable with a consecutive calcination and reduction treatment. Deactivation was concluded to be caused mainly by carbon deposition, with some W-leaching from the catalyst in the initial stages of reaction. The here demonstrated understanding of reaction kinetics and catalyst stability could facilitate the development of improved processes to produce hexane-1,2,5,6-tetrol from biomass.