Chapter 1.9 Kinetics of organic compounds chemisorption from the gas phase on oxides surface

Abstract

The models of chemisorption kinetics on the homogeneous and discrete heterogeneous surfaces describe poorly the kinetic isotherms of organic compounds in a whole range of surface coverage at different temperatures. Isosteric activation energies of these processes strongly depend on the surface coverage. This is due to different heterogeneity types of oxide surfaces. The proposed empirical equation including the power dependence of chemisorption apparent activation energy on the surface coverage allows it to describe the chemisorption kinetics of various organosilicon compounds on the Si, Ti, and Al pyrogenic oxides surface in a wide range of experimental conditions and to determine the activation energy and pre-exponential factor for surface modification. Effects of heterogeneous surface layer disordering and its topography can be studied using the solutions of simplified integral equations including the Gamma-distribution function on the chemisorption rate constants as well as the Gamma, normal or uniform distribution functions on the distances between neighboring sites with the account for lateral interactions between chemisorbed species in the mean-field approximation. A satisfactory qualitative agreement has been found between the present model predictions and the experimental kinetic data obtained for the organosilicon compound chemisorptions on the pyrogenic silica surface.