Glycerol hydrodeoxygenation to 1,2-propanediol catalyzed by CuPd/TiO^sub 2^-Na

• Published in: Applied catalysis. B, Environmental Vol. 219; p. 658
• Main Authors: Ardila, Alba N, Sánchez-Castillo, Marco A, Zepeda, Trino A, Villa, Aída Luz, Fuentes, Gustavo A
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier BV 15-12-2017
• Subjects: Acetone; Bimetals; Catalysis; Catalysts; Copper; Electron diffraction; Electron microscopy; Glycerol; High resolution electron microscopy; Hydrogenation; Nanoparticles; Palladium; Palladium base alloys; Reforming; Selectivity; Titanium dioxide; X-ray diffraction
• ISSN: 0926-3373; 1873-3883

Copper-palladium bimetallic catalysts supported on TiO2 were developed for the aqueous phase hydrodeoxygenation (HDO) of glycerol. Na-promoted bimetallic catalysts had higher activity than monometallic catalysts while maintaining high 1,2-propanediol (1,2-PDO) selectivity (76-93%) characteristic of Cu catalysts. The best results were obtained with CuPd/TiO2-Na. At 220 °C and 0.7 MPa H2 the initial turnover frequency (TOF based on Cu + Pd sites) was 0.14 s-1; the selectivity to 1,2-PDO reached 85%. Characterization of the samples was performed by H2-temperature programed reduction (H2-TPR), X-ray diffraction and high-resolution electron microscopy (HRTEM) plus selected area electron diffraction (SAED), and their results were consistent with the formation of CuPd alloy nanoparticles with their surface enriched in Cu, hence explaining the high selectivity to 1,2-PDO of the bimetallics. The increased activity of the Pd-Cu bimetallic catalysts stems from the significantly smaller average diameter of the CuPd alloy nanoparticles when compared with the Cu or Pd nanoparticles of the monometallic catalysts. Besides the effect upon the nanoparticle structure, Pd promoted HDO in part by the activation of glycerol aqueous phase reforming to produce H2 at the surface level. Cu was stabilized in the bimetallic samples by the formation of the alloy with Pd and by the presence of Na in the catalyst. As a result, CuPd/TiO2-Na can be reused while maintaining high stable activity and 1,2-PDO selectivity. The HDO reaction proceeds through the formation of 1-hydroxy-2-propanone (acetol), followed by its hydrogenation to form 1,2 PDO. Formation of acetol or an acetol-like surface intermediate presumably occurs on support sites, whereas the hydrogenation to 1,2-PDO occurs on the metal sites. The first step is enhanced when basic sites are added to the support, while the hydrogenation step on Cu sites is improved by raising the H2 pressure and/or by the formation of H2 via reforming on Pd sites.