Controlling surface reactivities of transition metals by carbide formation

Abstract

The surface reactivities of transition metals, including the Groups 4–6 early transition metals as well as the late transition metals of the 3d series, can often be modified by the formation of a carbide overlayer. More importantly, the reactivities of carbide-modified surfaces frequently demonstrate strong similarities to those of the Pt-group (Pt, Pd, Ir, Rh, Ru and Os) metals. In this paper, we will summarize our recent surface science investigations of the electronic, structural, and catalytic properties of well-characterized model carbide systems. Using several characteristic surface probing reactions, we will provide experimental evidence for the similar reactivities of the carbide-modified surfaces and the Pt-group metals. We will also discuss the underlying structural and electronic properties that are controlling the reactivities of the carbide-modified surfaces, such as the binding sites and chemical nature of the carbon atoms, the ionicity of the metal–carbon bonds, and the band structure of the transition metal carbides. We will also show examples of experimental attempts to correlate findings from the single crystal model carbide systems to amorphous powder carbide catalysts.