On inverse adsorption chromatography. 2. Determination of isotherms and heats of adsorption as well as energy distributions of adsorption sites

The isotherms and heats of adsorption, as well as the energy distributions of adsorption sites for pyridine at 100 °C and benzene at 40 °C on the silica surface, were determined by the method of inverse gas chromatography (IGC). These characteristics are usually obtained from IGC after integration of its direct result: the derivative of the adsorption isotherm. It is shown that the constant of integration plays a critical role in obtaining the isosteric heats of adsorption and the energy distributions of adsorption sites. The method of extrapolation is shown herein to be most appropriate for obtaining this constant. The modified ECP method, which takes account of longitudinal diffusion and kinetics of adsorption, was developed in the companion paper (Bakaev, V. A. J. Phys. Chem. C 2007, 111, 7463-7472) and was applied here to the pyridine/silica and benzene/silica systems. It is shown how to experimentally determine the longitudinal diffusion coefficient and the kinetics of adsorption coefficient. The IGC method probes only a small fraction of all of the adsorption sites on a surface. These are the strongest adsorption sites whose adsorption energy in the case of pyridine is almost 6 times larger in magnitude than the heat of liquefaction.