(20f) Hydrodeoxygenation of Fatty Acids in High-Temperature Water Using Molybdenum Carbide-Based Catalysts

The
hydrolysis of triglycerides produces fatty acids, which can then be upgraded to
produce hydrocarbons, direct replacements for petroleum-derived liquid fuels.
To date, most work has focused on the decarboxylation of fatty acids in organic
solvents or no solvent, using noble metals or alkali hydroxide catalysts [1-3].
Early transition metal carbides have been reported to have catalytic properties
that are similar to those of platinum group metals for several reactions [4]
and are known to be active for hydrodeoxygenation (HDO) [5-6]. In this paper we
report the rates and selectivities for a series of molybdenum carbide-based
catalysts and correlate these properties with pertinent structural and
compositional properties.

The molybdenum carbide
catalysts were found to be active and highly selective for the
hydrodeoxygenation of palmitic acid in high temperature water. The major
product was hexadecane and minor products included C₁₆ alkanes,
alcohols, and aldehydes. Smaller hydrocarbons were also observed suggesting the
presence of hydrogenolysis sites or thermal cracking.
X-ray diffraction of the spent catalyst revealed formation of some MoO₂,
indicating oxidation of the carbide catalysts. Deposition of metals onto the
carbide surface via wet impregnation resulted in a shift in selectivities and
stability.  These and other results
will be described in this paper.

In addition to the use of batch
reactors to screen the catalyst formulations, a flow reactor was used to elucidate
kinetics, reaction pathways, and behavior above and below the supercritical
point of water (374^oC, 22MPa). Results suggest that there is a shift
in kinetics and activity when in the supercritical vs.
subcritical regime, as seen in Figure 1. These results are correlated with high
temperature water properties, including dielectric constant, ionic product, and
density. These properties are highly tunable as a function of temperature and
pressure, as seen in Figure 2, and can lead a change in reactivity of the
medium.

References

1.     M.
Sn?re, I. Kubičkov?, P.
M?ki-Arvela, F. Chichova,K. Er?nen, and D.Y. Murzin, Fuel, 87, (2008) 933.

2.     I.
Simakova, O. Simakova, P. M?ki-Arvela, D.Y. Murzin,
Catalysis Today, 150, (2010) 28.

3.     J.
Fu, X. Lu, P.E. Savage, Energy Environ. Sci., 3, (2010) 311.

4.     S.T.
Oyama, Catalysis Today, 15, (1992) 179.

5.     J.
Monnier, H. Sulimma, A.
Dalai, G. Caravaggio, Applied Catalysis A: General,
382, (2010) 176.

6.     J.
Han, J. Duan, P. Chen, H. Lou, X. Zheng, H. Hong, Green Chemistry, 13, (2011)
2561.

7.     H.
Weingarter, E. U. Franck, Angweandte
Chemie, 44 (2005) 2672.