Synthesis and catalytic properties of vanadium interstitial compounds

Vanadium nitrides and carbides were synthesized by the temperature-programmed reaction of vanadium oxide (V2O5) With pure NH3, and with pure CH4 or a mixture of 49.9% CH4 in H-2, respectively. Based on the XRD results, the materials contained VN or VN with a negligible amount of V2O3 in the bulk after the nitridation of vanadium oxides and only V8C7 after the carburization. These results indicated that the structural properties of these materials were strong functions of the heating rate and space velocity employed. The vanadium nitrides and carbides proved to be active NH3 synthesis and decomposition catalysts. Since the activity varied with changes in the surface area and particle size, ammonia decomposition over the vanadium nitrides and carbides appeared to be structure-sensitive. This response was considered to be due to variations in the surface stoichiometry with particle size. In general, the activities of the vanadium carbides were about 1 to 2 orders of magnitude lesser than that of Mo nitride catalyst while vanadium carbides had higher activities by a factor of 1 or 2 than Pt/C catalyst. However, the activity of the lowest surface area vanadium carbide is similar to that of Mo nitride catalyst. (C) 1998 Elsevier Science B.V.