Highly Selective Conversion of Glycerol to Formic Acid over a Synergistic Au/Phosphotungstic Acid Catalyst under Nanoconfinement

Converting surplus glycerol into the hydrogen storage material, formic acid, can meet the increasing energy demand, yet its commercial production is hindered by the low efficiency. Herein, a nano-confined catalytic system with multiple active sites that consists of ultrasmall Au nanoparticles (NPs) and highly dispersed phosphotungstic acid (PTA) within the nanochannels of mesoporous silica nanoparticles (Au-PTA/MSN) was demonstrated to directly convert glycerol to formic acid in a one-step operation under the mild condition with a selectivity of up to 79.2%. The time-course experiment revealed that such a one-pot process involves synergistic catalysis from glycerol to a triose, followed by the breakdown of the C-C bond of trioses into glycolic acid and formic acid, as well as further oxidative cleavage of glycolic acid to formic acid, which eventually contributed to the highly selective formic acid production. Characterizations showed that the nano-confined Au-PTA/MSN catalytic system incorporated the catalytic actions of Au NPs and phosphotungstic acid in one operation, thus offering a high activity for converting glycerol to formic acid.