Significance of isomeric reaction intermediates in the hydrogenolysis of glycerol to 1,2-propanediol with Cu-based catalysts

• Published in: Catalysis science & technology 2017, Vol.7 (14), p.3119-3127
• Main Authors: Vila, F., López Granados, M., Mariscal, R.
• Format: Article
• Language: English
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/C7CY00603A

Cu/γ-Al 2 O 3 catalysts were studied in the aqueous hydrogenolysis of glycerol to obtain 1,2-propanediol (1,2-PDO). These samples were characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy using adsorbed hydroxypropanone (acetol) in the presence of Ar or H 2 . Moreover, 1 H nuclear magnetic resonance ( 1 H-NMR) was used to identify the reaction products that formed when deuterated glycerol was hydrogenated in deuterated water. The DRIFT spectra revealed that enediol species are mainly stabilized at the surface of the reduced CuAl catalyst. The 1 H-NMR data indicated that the reduction of the 2,3-dihydroxy-1-propene (2,3-enediol) isomer is kinetically favored to form 1,2-PDO, whereas the 1,2-dihydroxy-1-propene (1,2-enediol) species needs to first be converted to a 2-hydroxypropanal (2-OH-propanal) isomer. Therefore, the stabilization and reducibility of these enediol isomers were considered essential for the selectivity in the formation of 1,2-PDO. In addition, acetol oxidation through an interaction with surface Cu 2+ or Cu + and subsequent production of chemisorbed lactate should be avoided. A reaction mechanism with the participation of the different acetol intermediate isomers has been proposed.