(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.