The Highest Chemoselective Conversion of Glycerol to Lactic Acid by Ethylene-Stabilized Carbon-Supported Platinum Nanoparticles

Lactic acid (LA) is an important synthetic intermediate to obtain useful products. Recently, the demand of LA greatly increased because of its use as monomer in the production of biodegradable poly(lactic acid) (PLA), which is a an environment friendly alternative to plastics derived from petrochemical materials. Enatiomerically pure LA is mainly obtained through the fermentation of sugars under anaerobic conditions; however, the process is environmental unfriendly since it produces a huge amount of calcium sulfate.2 The metal-assisted conversion of glycerol (GLY) to LA using oxygen as hydrogen acceptor with heterogeneous Pt-Au bimetallic catalysts has been reported as an alternative synthesis protocol. Unfortunately, the excess of a Brønsted base (e.g. NaOH), necessary to convert pyruvaldehyde to LA, in presence of oxygen leads the formation of undesired side-products decreasing LA chemoselectivity (85% at most). Chaudhari et al. showed a LA chemoselectivity of 80% with Cu-based catalyst using only a stoichiometric amount (1:1 GLY /NaOH molar ratio) but very high reaction temperatures (473-513 K). We report here the highest chemoselective conversion of GLY to LA found for a heterogeneous catalyst using small-sized monodispersed Pt-nanoparticles (NPs) generated by metal-vapor synthesis (MVS)7,8 and supported onto Ketjenblack carbon (Pt/Ck) in presence of ethylene as hydrogen acceptor. Ethylene atmosphere both prevent the formation of oxidation side-products and stabilize NPs from aggregation leading to a high reusability of the catalyst.