Contribution of a Repulsive Potential in a Micropore Volume Filling. A Surface of Micropore Walls

Abstract

In the case of narrow micropores, a volume filling of the single micropore and a two-dimensional condensation on its walls occur at the same condensation pressure, and the local adsorption behavior may be modeled by the condensation approximation. Proceeding from (i) the accepted model of carbon heterogeneity, (ii) the theory of adsorption on homogeneous surfaces considering lateral interactions, and (iii) the 10−4 potential function, the correlation between a micropore filling pressure, p, and a micropore reduced half-width, d/r0, is derived. This approach provides a correct description of equilibrium data in a range of p/ps ≈ 5 × 10-7 to 0.2 at 293 K and leads to reasonable distribution functions of micropore sizes and adsorption energies. The model contains a specific prediction that there is a minimum filling pressure, pmin, that corresponds to the maximum adsorption energy at d/r0 = 1 and determines the lower boundary of the micropore volume filling. For benzene adsorption at 293 and 423 K, the pmin/ps values are equal to 7.36 × 10-8 and 1.15 × 10-5, respectively. When p < pmin, only a submonolayer adsorption occurs on a micropore surface. The expression for the calculation of a micropore surface is derived, and the underlying assumption is discussed.