Controlling reaction pathways of selective C–O bond cleavage of glycerol

Abstract

The selective hydrodeoxygenation (HDO) reaction is desirable to convert glycerol into various value-added products by breaking different numbers of C–O bonds while maintaining C–C bonds. Here we combine experimental and density functional theory (DFT) results to reveal that the Cu modifier can significantly reduce the oxophilicity of the molybdenum carbide (Mo2C) surface and change the product distribution. The Mo2C surface is active for breaking all C–O bonds to produce propylene. As the Cu coverage increases to 0.5 monolayer (ML), the Cu/Mo2C surface shows activity towards breaking two C–O bonds and forming ally-alcohol and propanal. As the Cu coverage further increases, the Cu/Mo2C surface cleaves one C–O bond to form acetol. DFT calculations reveal that the Mo2C surface, Cu-Mo interface, and Cu surface are distinct sites for the production of propylene, ally-alcohol, and acetol, respectively. This study explores the feasibility of tuning the glycerol HDO selectivity by modifying the surface oxophilicity.

Vibrational Spectroscopic Characterization of Glycerol Reaction Pathways over Metal‐Modified Molybdenum Carbide Surfaces

“…In contrast, on the Mo 2 C surface, the intensity of the (CO) mode was reduced, confirming the C−O bond cleavage and being consistent with the lower onset temperature of the propylene desorption from the fresh Mo 2 C surface than on Fe/Mo 2 C (Figure (b)). On Cu/Mo 2 C, the decrease of the v(CO) mode intensity was consistent with the formation of C−O bond scission products and the desorption of acetol, as reported previously . In summary, the HREELS results indicated that Mo 2 C interacted with the oxygen in glycerol more strongly than Fe/Mo 2 C and Cu/Mo 2 C, and Pt/Mo 2 C showed reforming activity.…”

“…With the addition of Pt modifier on Mo 2 C, the reaction pathway of glycerol changed from HDO to reforming. On Cu/Mo 2 C, glycerol only underwent one C−O bond scission to form acetol (Figure (d)), likely due to the lower oxophilicity of the Cu modifier. Comparing the reaction pathways on these four surfaces (Scheme ), Mo 2 C and Fe/Mo 2 C were able to cleave all the C−O bonds in glycerol to produce propylene, Cu/Mo 2 C broke only one C−O bond of glycerol to form acetol, while Pt/Mo 2 C favored the C−C and C−H bond scissions to produce CO and H 2 .…”

“…The reforming reaction breaks the C−H and C−C bonds of glycerol to form syngas (CO+H 2 ) for methanol production and Fisher‐Tropsch synthesis . The complete hydrodeoxygenation (HDO) reaction can cleave all the C−O bonds of glycerol to produce propylene, an industrially important building block . The propylene produced from glycerol can contribute to the on‐purpose production to fill the current gap between propylene market demand and supply .…”

“…In a previous study, the selective HDO reaction of glycerol was investigated on Cu‐modified Mo 2 C catalysts . The combination of a strongly oxophilic site, Mo, and a weakly oxophilic sites, Cu, can selectively break a different number of C−O bonds of glycerol, leading to the selective production of propylene, allyl−alcohol, propanal, and acetol on Cu/Mo 2 C surfaces with different Cu coverages.…”

“…In this work, Pt/ Mo 2 C and Fe/Mo 2 C surfaces have been investigated to determine the effect of metal modifiers in controlling the reaction pathways of glycerol. The results from Cu‐modified Mo 2 C surface were also referred to for comparison . Consecutive TPD measurements were used to determine the surface activity and stability, and vibrational spectroscopic studies using high‐resolution electron energy loss spectroscopy (HREELS) were performed to identify the surface intermediates.…”