On the preparation of molybdenum carbide-supported metal catalysts

Carbide-supported metal catalysts have been demonstrated to be highly active for a number of reactions including water gas shift and electrochemical hydrogen evolution. Their activity appears to be a consequence of intimate interactions between the metal and support. These interactions as well as the structures and compositions depend on the conditions used during preparation. The objective of research described in this paper was to define key aspects regarding the adsorption and reaction of metal precursor complexes with unpassivated, high surface area Mo2C powders during wet impregnation. The rate of metal deposition and the final state of the metal were functions of the nature of the precursor (i.e., counter ion), electrostatic interactions, and red–ox reactions with the Mo2C surface. The deposition rate decreased in the following order: H2PtCl6 ∼ Pd(NH3)4(NO3)2 ∼ CuCl2 ∼ Cu(NO3)2 > Co(NO3)2 ∼ Ni(NO3)2 ≫ CoCl2 ∼ NiCl2 ∼ FeCl2 ∼ Fe(NO3)3. The observed adsorption and red–ox behavior suggest that supporting metals onto native carbide surfaces could result in properties that are significantly different from those for metals supported on oxidized carbide surfaces.

The deposition of metals onto the native Mo2C surface was influenced by electrostatic interactions and a surface red-ox reaction. For the Pt, Pd and Cu precursors, the Mo2C support was capable of reducing the metal complex to its zero-valent state.Figure optionsDownload high-quality image (52 K)Download as PowerPoint slideHighlights
► Key aspects regarding interaction of metal precursors with unpassivated Mo2C elucidated.
► Deposition of metals on Mo2C was first order with respect to precursor concentration.
► Electrostatic interactions appeared to be important for adsorption of several precursors.
► Unpassivated Mo2C was able to reduce several precursors to zero-valent metals.