Silica-Templated Synthesis of Ordered Mesoporous Tungsten Carbide/Graphitic Carbon Composites with Nanocrystalline Walls and High Surface Areas via a Temperature-Programmed Carburization Route
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Abstract
Ordered mesostructured tungsten carbide and graphitic carbon composites (WC/C) with
nanocrystalline walls are fabricated for the first time by a temperature-programmed
carburization approach with phosphotungstic acid (PTA) as a precursor and mesoporous
silica materials as hard templates. The mesostructure, crystal phase, and amount of
deposited graphitic carbon can be conveniently tuned by controlling the silica template
(SBA-15 or KIT-6), carburizing temperature (700-1000 degrees C), the PTA-loading amount,
and the carburizing atmosphere (CH(4) or a CH(4)/H(2) mixture). A high level of deposited
carbon is favorable for connecting and stabilizing the WC nanocrystallites to achieve
high mesostructural regularity, as well as promoting the carburization reaction. Meanwhile,
large pore sizes and high mesoporosity of the silica templates can promote WC-phase
formation. These novel, ordered, mesoporous WC/C nanocomposites with high surface
areas (74-169 m(2) g(-1)), large pore volumes (0.14-0.17 cm(3) g(-1)), narrow pore-size
distributions (centered at about 3 nm), and very good oxidation resistance (up to
750 degrees C) have potential applications in fuel-cell catalysts and nanodevices.