(544ew) Indirect Oxidation of Glucose to Glucuronic Acid Using Pd-Decorated Au Catalysts

Glucuronic acid is a valuable chemical precursor for use in the pharmaceutical and food industries. It currently is produced via the aerobic enzymatic oxidation of glucose at the C₆ position by Ustulina deusta bacteria and Bacterium industrium var. Hoshigaki. However, microbe separation, low process productivity and selectivity, and the disposal/recycling of wastewater limit practical production. In this study, we explored the possibility of heterogeneous catalysts to produce glucuronic acid from glucose via a methyl glucoside pathway. We tested monometallic Au and Pd and bimetallic Pd-on-Au nanoparticles as model catalysts for the aqueous-phase oxidation of methyl glucoside under aerobic conditions at mild temperature and pressure. The Pd-on-Au nanoparticles consist of a 4-nm Au core decorated with Pd metal (whose content is quantified as Pd surface coverage), which are then supported on carbon prior to reaction testing. Pd-on-Au/C exhibited a volcano-shaped catalytic activity dependence on Pd surface coverage, with the optimal initial turnover frequency (TOF) of 413 h^-1 observed at 80 sc% Pd, a rate >5x faster than Au/C or Pd/C. Methyl-glucuronide (from selective oxidation at the C₆ position) was the dominant product, which can be demethylated to form glucuronic acid. Pd-on-Au oxidation of methyl glucoside could be a greener approach to the glucuronic acid synthesis.