Selective aerobic oxidation reactions of polyols, which produce various carbonyl compounds, are attracting increasing interest in current chemistry, due to their importance in sustainable chemistry in relation to valorization of bio-derived molecules. Reported herein are the distinctive catalysis of supported Au (Au/TiO2, Au/Al2O3, Au/ZrO2) and Pt (Pt/Al2O3, Pt/C) nanoparticles (NPs) in aerobic oxidation of C3-polyols including glycerol (GL), 1,2- (1,2-PDO) and 1,3-propandiol (1,3-PDO) either in NaOH-free or NaOH-containing water. The catalytic data in NaOH-fee (or pH&lt; 7) water at 60-90 °C clearly show that the Pt and Au NPs are, respectively, highly selective catalysts for the oxidation of the terminal and central HO-bound carbons in the reaction of GL and 1,2-PDO. In the oxidation of 1,3-PDO, the dominant product was 3-hydroxypropanal (3-HPD) over the Pt but 3-hydroxypropionic acid (3-HPA) over the Au NPs, suggesting that Pt was highly efficient for oxidizing one of the terminal HO-bound carbons to the corresponding aldehyde but Au was instead highly efficient for oxidizing the primary aldehyde to the carboxylic acid. The distinctive selectivity of Pt and Au catalysts is further confirmed by including 1- and 2-propanol in the catalytic reaction study. The differences between the catalysis of Pt and Au NPs became less distinguishable when the oxidation reactions were conducted in basic or NaOH-containing water, due to promotional function of the base during the catalysis. The base also greatly promoted the ketone-to-aldehyde conversion, then the formation of carboxylic acid (carboxylate) from the aldehyde during the oxidation of GL and 1,2-PDO; for 1,3-PDO oxidation, both Pt and Au catalysts gave 3-HPA as the dominant product. Molecular insight into the catalytic mechanisms is generated by rigorous experimental assessments of the substrate reactivity and product selectivity, and by DFT evaluation of the energy barriers for the possible elemental reactions, which will be presented at the meeting.

Distinctive catalysis of supported Pt and Au nanoparticles in aerobic oxidation of polyols

253rd National Meeting (2017)

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