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

摘要

As the production of biodiesel increases, it is economically preferable to upgrade the excess by-product, glycerol, into value-added products. Metal-modified molybdenum carbide (Mo2C) is a class of promising catalysts for this application due to their promising hydrodeoxygenation (HDO) activity. In this work, Pt, Fe and Cu were used to modify the Mo2C surface and tune the product selectivity of glycerol. Pt/Mo2C showed reforming activity to produce syngas, Fe/Mo2C cleaved all the C-O bonds of glycerol to produce propylene, while Cu/Mo2C broke only one C-O bond of glycerol to form acetol. Consecutive temperature-programmed desorption (TPD) experiments demonstrated an enhanced stability of all surfaces when compared to Mo2C. High-resolution electron energy loss spectroscopy (HREELS) characterization indicated that the Fe/Mo2C surface weakened the C-O bonds of glycerol, while the Pt/Mo2C surface showed no activity towards C-O bond cleavage. This study demonstrated that the Pt/Mo2C, Fe/Mo2C and Cu/Mo2C surfaces were active, selective and stable for converting glycerol into syngas, propylene, and acetol, respectively. The combination of TPD and HREELS also served as an example of utilizing surface spectroscopy to identify the reaction pathways and intermediates on model catalyst surfaces. This should, in turn, provide insights to guide the design of metal-modified carbide catalysts for the upgrading of biomass-derived oxygenates.