Biodiesel is an important renewable resource for addressing energy and environmental challenges of current society1,2
. Glycerol is a major byproduct of biodiesel production3
and can be upgraded into value-added products via the selective hydrodeoxygenation reaction. In this work, we demonstrated the selective tuning of the C-O bond cleavage sequence of glycerol by varying the Cu coverage on Mo2
C. Temperature Programmed Desorption (TPD) results show that the Mo2
C surface cleaves all the C-O bonds of glycerol to produce propylene; the Cu/Mo2
C interface tends to cleave a primary and a secondary C-O bond of glycerol to form allyl alcohol; the Cu surface prefers to break a primary C-O bond to form acetol. Surface vibrational studies indicate that glycerol undergoes initial O-H scission on Mo2
C and the C-O bonds are weakened due to the strong interaction between the oxygen in glycerol and Mo2
C. As Cu coverage increases, the O-H bonds of glycerol are preserved, and the O-Mo interaction is reduced. Activation barrier calculations from DFT further reveal the different bond-breaking capability of the Mo site, Mo-Cu interface and Cu site on Cu/Mo2
C due to their different oxygen binding energies. The combined model surface experiments and DFT calculations suggest the feasibility of selectively controlling the C-O bond breaking sequence of glycerol to produce desired products. Efforts have also been devoted to searching model compounds for glycerol in order to bridge the pressure and material gaps between model surfaces and powder catalysts. This work should provide insights into the rational design of more efficient catalysts for the upgrading of glycerol and potentially other biomass-derived polyols.
1 H. M. Mahmudul, F. Y. Hagos, R. Mamat, A. A. Adam, W. F. W. Ishak and R. Alenezi, Renew. Sustain. Energy Rev., 2017, 72, 497â509.
2 J. Hill, E. Nelson, D. Tilman, S. Polasky and D. Tiffany, Proc. Natl. Acad. Sci., 2006, 103, 11206â11210.
3 C. DâAgostino, G. Brett, G. Divitini, C. Ducati, G. J. Hutchings, M. D. Mantle and L. F. Gladden, ACS Catal., 2017, 7, 4235â4241.