Compounds of molybdenum and tungsten with high specific surface area: I. Nitrides

Abstract

Temperature-programmed reaction between MoO₃ or WO₃ with NH₃ provides a new way to prepare Mo₂N and W₂N powders with specific surface areas as high as 220 and 91 m² g⁻¹, respectively, corresponding to 3- to 4-nm crystallites. The transformation of MoO₃ platelets is topotactic in the sense that {100} planes of Mo₂N are parallel to {010} planes of MoO₃. As the MoO₃ reacts with NH₃, it passes through an oxynitride intermediate with changing bulk structure, increasing surface area, and decreasing oxidation state of the metal. The product consists of highly porous nitride platelets, pseudomorphous with the original MoO₃.