Synthesis and catalytic properties of vanadium interstitial compounds

Abstract

Vanadium nitrides and carbides were synthesized by the temperature-programmed reaction of vanadium oxide (V 2O 5) with pure NH 3, and with pure CH 4 or a mixture of 49.9% CH 4 in H 2, respectively. Based on the XRD results, the materials contained VN or VN with a negligible amount of V 2O 3 in the bulk after the nitridation of vanadium oxides and only V 8C 7 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 NH 3 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.