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.