Preparation and catalytic properties of transition metal carbides and nitrides

Interstitial alloys are formed by the incorporation of carbon, nitrogen and oxygen into the lattices of early transition metals to produce a class of compounds with metallic character. The crystal structure of the materials is similar to that of the metals, with the metal atoms usually forming closed-packed lattices. The compounds can now be prepared in very high surface area form by a number of methods. They have excellent catalytic activity in a wide variety of reactions: ammonia synthesis and decomposition, hydrogenolysis, isomerization, methanation, and hydroprocessing. In particular, for hydrogenation type reactions they display activity approaching or surpassing those of the best Group 8 metals. Although their activity is similar to those of the noble metals, kinetics and product selectivities are often different and indicate that the carbides and nitrides provide unique catalytic pathways.