1 INTRODUCTION

This paper is devoted to considerations of the role of surface carbon in modifying surface reactivity, an area to which Geoff Webb has contributed significantly during his career [1, 2]. It is generally considered that surface carbon is a poison for many reactions. Indeed, in the strict sense this is usually true (that is, as carbon builds up on a surface and total activity goes down). However, in this paper we give some examples of surface reactivity which show that carbon can have a very positive role to play in manipulating reaction selectivity, so much so that it can result in higher activity to desired products.

Geoff Webb has been involved in this area during his years of contribution to the field of surface reactivity and catalysis. In particular he noted that the presence of carbon on metal surfaces may take a direct role in the catalysis of butene hydrogenation, by acting as a surface hydrogen exchange medium between hydrogen in the gas phase and the adsorbed olefin [2]. These kinds of ideas were extended by Somorjai [3] and others to hydrocarbon reactivity on surfaces by identifying the presence of certain intermediates on the surface (e.g. ethylidyne [4]). He also recognised that, although the metal surface can contain a very large amount of surface C, nevertheless hydrocarbon reactions can still proceed...