The Chemisorption of Hydrocarbons

Abstract

PREFACEWe have considered at some length the ways in which hydrogen can interact with metals and supported metal catalysts, and with itself when isotopic analogues are used, and because our main theme is the reactions that hydrogen undergoes with hydrocarbons it is logical that we should next examine how they interact with metal surfaces. The great variety of types of hydrocarbon (alkanes, alkenes, alkynes, aromatics etc.) make this potentially a much larger subject than that of the last Chapter, and a further complication is that the forms adopted by a specific hydrocarbon depend on the nature of the metal, the crystal plane, the particle size, and particularly the temperature. These factors have acted as a challenge to experimentalists and theoreticians, and there is a very extensive literature, on which it will be necessary to try to impose some order; selection and compression will also be called for.Our aim will be to try to identify those adsorbed species most likely to be intermediates in the reactions we shall meet later, and to recognise species derived from the original molecule that may inhibit the desired reaction, or indeed be required for reaction under more forcing conditions. In some cases the structure of the relevant intermediate looks like that of the product, and, just as with hydrogen, the essential part of the process is accomplished in the chemisorption. The very precise and detailed information available on the structures of certain adsorbed species and their effects on the arrangement of surface metal atoms will excite our admiration. 153 154 CHAPTER 4