(482c) Molybdenum Carbide-Supported Metal Catalysts: Synthesis, Characterization, and Catalytic Properties | AIChE

(482c) Molybdenum Carbide-Supported Metal Catalysts: Synthesis, Characterization, and Catalytic Properties


Schaidle, J. A. - Presenter, University of Michigan
Schweitzer, N. M. - Presenter, The University of Michigan
Thompson, L. - Presenter, University of Michigan

Early transition metal carbides have been shown to be active for a variety of reactions [1] and tolerant to sulfur poisoning for some reactions [2]. Moreover, these materials can be synthesized with high surface areas [3], leading to their use as supports for other metals. For example, a Pt/Mo2C catalyst produced by depositing Pt directly onto the native Mo2C surface [4] was demonstrated to be more active than conventional catalysts for reactions such as water gas shift [5] and methanol steam reforming [6]. The basis for this high activity remains ill-defined.

A series of Mo2C supported Pt, Pd, Cu, Ni, and Fe catalysts was synthesized and characterized using x-ray absorption spectroscopy (XAS) and high resolution transmission electron microscopy (TEM). These catalysts were highly active for the water gas shift and Fischer-Tropsch Synthesis reactions. The XAS results indicated that the PtCl62- complex was reduced to metallic Pt on the surface of Mo2C during the adsorption process. This result is in agreement with our ability to attain high Pt loadings (>12 wt%) and high dispersions. The Pd (Pd(NH3)4(NO3)2) and Cu (CuCl2) complexes also produced high metal dispersions on adsorption to Mo2C; however, the Ni (NiCl2) and Fe (FeCl2) precursors did not. We believe the driving force for reduction of the Pt, Pd, and Cu complexes was a redox reaction between the metal complex in solution and the Mo2C surface whereby the metal complex was reduced and the Mo2C surface was oxidized.

The TEM and XAS are consistent with Pt that was in the form of ?raft-like? particles wetting the Mo2C surface. As the Pt loading increased, the diameter of these rafts increased, but the thickness appeared to remain constant. Work is in progress to exploit the strong interactions between the PtCl62- complex and Mo2C in the synthesis of core shell particles on Al2O3 and carbon supports.

[1] S. T. Oyama, Catalysis Today 15 (1992).

[2] E. J. Markel, J. W. Van Zee, Journal of Catalysis 126 (1990).

[3] J. S. Lee, S. T. Oyama, M. Boudart, Journal of Catalysis 106 (1987).

[4] L. T. Thompson, S. K. Bej, J. J. Patt, C. H. Kim, US Patent 6897178 (2005).

[5] T. E. King, Ph. D. Thesis, University of Michigan, 2007.

[6] W. Setthapun, S. Bej, L. T. Thompson, Top. Catal. 49 (2008).