Preparation, interconversion and characterization of nanometer-sized molybdenum carbide catalysts

Nanometer-sized molybdenum carbide particles have been shown to have hydrogenation and other catalytic properties similar to those of the more-expensive noble metals. However, current preparation techniques for molybdenum carbide require the high-temperature reduction of unsupported molybdenum oxide in the presence of CH₄ and H₂. Although this method is effective, it yields particles of relatively large size, 11 nm. Different, simpler, synthesis procedures starting with ammonium heptamolybdate impregnated on carbon yield carbides of different stiochiometries. Particle sizes are in the 2–10 nm range, which are generally smaller than those previously obtained, and can be altered by changing the method of preparation. The focus of this work is to characterize the new procedures, specifically the bulk transitions of the new starting material to the different molybdenum carbides, using time-resolved X-ray diffraction, temperature-programmed reduction, and temperature-programmed desorption.