| Abstract
| - The synthesis of high-surface-area molybdenum carbides has been studied by thetemperature-programmed carburization of molybdenum trioxide MoO3. The feedstocks usedwere mixtures of methane and ethane with hydrogen. The solid reaction products werecharacterized at selected intervals using thermogravimetric analysis differential scanningcalorimetry (TGA-DSC), surface area measurement (BET), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The gaseous products of thecarburization process were monitored using a gas chromatograph equipped with a massspectrometer (GC-MS). The structural properties of the product carbides are shown to dependon the conditions of synthesis. The C2H6/H2 feedstock gave the highest-surface-area material.The presence of H2 in the feed mixture reduced the amount of amorphous carbon depositedan the molybdenum carbide material. The surface area was found to increase most rapidlyduring the initial H2-reduction stage. Initially, the MoO3 is reduced to form MoO3-x. Thismaterial has structural defects, which can account for a decrease in the average particlesize and an increased porosity, resulting in an increased surface area. During thecarburization process, three phase transitions are observed. At higher temperatures, therate of deposition of graphitic and amorphous carbons derived from CH4 or CO is muchgreater than the rate of hydrogenation of the deposited carbon, resulting in the formationof surface graphitic carbon.
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