ABSTRACT
The physical structure of a surface, its area, morphology and texture and the sizes of orifices and pores are often crucial determinants of its properties. For example, catalytic reactions take place at surfaces. Simple statistical mechanical estimates suggest that a surface-mediated reaction should proceed about 1012 times faster than the corresponding gas-phase reaction for identical activation energies [1]. The catalyst operates by lowering the activation energy of the reaction to accelerate the rate. The reaction rate, however, also increases in proportion to the exposed surface area of the active component of the catalyst so that maximizing its area also strongly affects its activity. Catalysts often have complicated morphologies, consisting of exposed regions, and small micro-and meso-pores. A traditional method for measuring these areas, which is still the workhorse for the catalytic chemists, is to titrate the surface with molecules of known ‘areas’ and to measure the amount that just covers it. This is done by pressurizing the sample using probe gases and gauging when a single layer of adsorbate forms. This relies on developing robust theoretical methods for determining the equilibrium between the gas phase and the surface. This was done in 1938 by Brunauer, Emmett and Teller. Brunauer and Emmett were catalytic chemists and Teller a theoretical physicist who was persuaded to undertake the theoretical task of developing an adsorption isotherm [2]. This he apparently did in one day and the Brunauer-Emmett-Teller isotherm was born. This, with minor modifications, is the isotherm still used today.
