Thermodynamic factors in adsorption and catalysis—equilibria in the adsorbed phase

Abstract

Chemisorption and catalysis of complex molecules or mixtures involve the establishment of some but not necessarily all the possible equilibria between gas and surface and between different kinds of species on the surface. Each such equilibrium established necessarily exerts a thermodynamic influence on the amounts of the various adsorbed species which take part in the kinetically controlled processes associated with the adsorption or the catalysis. Problems of this kind are discussed and emphasis is placed on the importance of using the correct functions of pressure in expressions to describe the amounts of radicals and atoms on surfaces. The use of the concept of a virtual pressure is also advocated for situations where some but not all of the molecules in the gas phase are equilibrated with the surface.