The Impact of V Doping on the Carbothermal Synthesis of Mesoporous Mo Carbides

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Abstract

A series of bimetallic carbides of the form β-(Mo1–xVx)2C (0 < x < 0.12) was synthesized by carbothermal reduction of corresponding h-Mo1–xVxO3 precursors. The oxides were synthesized by precipitation, and the subsequent carbide phase development was monitored. The reduction mechanism is discussed on the basis of observed structural evolution and solid-state kinetic data. The reduction is observed to proceed via a complex mechanism involving the initial formation of defective MoIV oxide. Increasing the V content retards the onset of reduction and strongly influences the kinetics of carburization. The carbides exhibit a trend in the growth morphology with V concentration, from a particulate-agglomerate material to a packed, nanofibrous morphology. The high-aspect-ratio crystallites exhibit pseudomorphism, and in the case of the V-containing materials, some preferential crystal orientation of grains is observed. An increasing mesoporosity is associated with the fibrous morphology, as well as an exceptionally high surface area (80–110 m2/g). The synthesis was subsequently scaled up. By adapting the heating rate, gas flow, and pretreatment conditions, it was possible to produce carbide materials with comparable physical properties to those obtained from the small scale. As a result, it was possible to synthesize Mo2C materials in multigram quantities (5–15 g) with BET surface areas ranging from 50 to 100 m2/g, among the highest values reported in the literature.

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