(676b) "Molybdenum Carbide As a Potential Catalyst for Olefins Hydrogenation"

There is a vital necessity in the suppression of olefins from upgraded heavy oil fractions. These deleterious molecules can form gum deposits on equipment and polymerize in pipelines over time during oil transportation, resulting in the fouling of heat exchangers and possible formation of coke. Most of the catalysts used so far in olefins hydrogenation, are expensive noble metals, such as Pt, Pd and Ru. In addition, these catalysts are vulnerable to sulfur poisoning, especially when used with heavy oil feedstocks. Novel inexpensive molybdenum carbide (Mo₂C) catalysts with nanocrystalline size domains have been synthesized in our laboratory at lower temperatures than previously reported.^1,2  Our cost-effective synthetic approach now allows us to obtain good control over physical properties and structure of the carbide along with catalyst scale-up. The prepared material showed high activity towards the selective hydrogenation of aromatics at temperatures below 200 ^o C, producing methyl-cyclohexane, when toluene was used as a model molecule in a bench scale hydrogenation setup.^2,3

More suprisingly, our preliminary results using the above mentioned catalyst showed that it is possible to hydrogenate aromatics at very low pressures (< 100 psi) while still maintaining an excellent selectivity and catalyst stability. Activity of the proposed catalyst towards aromatics at low pressures and temperatures has directed our attention that it could be possible to hydrogenate olefins at even milder reaction conditions, as olefins hydrogenation is generally thermodynamically favored at lower temperatures and pressures compared to aromatics. Thus, heterogeneous catalytic hydrogenation of 1-octene as an olefinic model molecule was tested on bulk cubic Mo₂C. The selective conversion of 1-octene to n-octane occurred in a timely manner. In addition, the cubic Mo₂C active phase transformed into the hexagonal Mo₂C phase during both toluene and 1-octene hydrogenation reactions, as confirmed by XRD analysis; however, without affecting the activity and selectivity towards the desired hydrogeneted products. Another designed carbide catalyst, which is the cubic Mo₂C impregnated onto commercially available alumina spheres, has also been tested for 1-octene hydrogenation. Decreasing the carbide active phase amount by its impregnation on alumina did not show a decrease in catalyst activity or selectivity when compared to the bulk cubic Mo₂C. This shows that less amounts of carbide active phase can be used when this carbide is supported on alumina towards olefins hydrogenation.

References

[1] K. Leary, J. Michaels, A. Stacy, J. Catal. 101 (1986) 301–313.

[2] G. Vitale, M. Frauwallner, C. Scott, P. Pereira-Almao, J. Appl. Catal. A: Gen. 408 (2011) 178-186.

[3] G. Vitale, H. Guzman, M. Frauwallner, C. Scott, P. Pereira-Almao, Catal. Today. 250 (2015) 123-133.