Kinetics of activated chemisorption. Part 3.—Amount and distribution of adsorbate at varying temperatures and pressures

Abstract

The heterogeneous-surface model applied in Part 2 to the kinetics, is now applied to the effects of temperature and pressure on the amount adsorbed. It predicts isobars with a maximum that is displaced towards higher temperatures at higher pressures. The low-temperature, pseudo-equilibrium isotherms obey the Freundlich equation. Increase in temperature or decrease in pressure produce desorption followed by readsorption. Temperature-programmed desorption gives one peak when heating is slow and two peaks when heating is rapid. When isotopes are successively adsorbed, the isotope adsorbed last is desorbed at lower temperature. The distribution of the adsorbate, according to the regions of various energy on the adsorbent, depends on temperature, pressure and time and is given by a discontinuous function with a maximum.