Abstract

Heterogeneous glycerol (GLY) oxidation offers a promising route for the production of lactic acid (LA), a key monomer in biodegradable bioplastics. However, the specific reaction pathways remain poorly understood. This study presents a mechanistic investigation of GLY oxidation to LA using Pt/Sn-MFI catalysts. Characterizations via DR-UV-Vis spectroscopy, 119Sn NMR, and TEM reveal the formation of zeolite framework Sn and well-dispersed Pt nanoparticles in Pt/Sn-MFI. The Lewis acidity of framework Sn in MFI zeolite is confirmed through 31P NMR probe techniques. GLY conversion and LA selectivity correlate strongly with framework Sn concentration and the presence of Pt nanoparticles. In situ13C solid-state NMR experiments, complemented by two-dimensional 13C correlation NMR, allow real-time monitoring of GLY conversion and identification of various mobile and rigid (surface-adsorbed) species. Results indicate that GLY preferentially transforms to LA via a dihydroxyacetone (DHA) intermediate, facilitated by the Pt-Sn synergistic effect. However, accumulation of surface-adsorbed LA on Sn sites promotes consecutive oxidation of GLY to glyceric acid, tartaric acid, and ultimately CO2.

Link:https://link.springer.com/article/10.1007/s40242-024-4168-4