Mathematical Analysis of Physicochemical Processes on Catalytic Surfaces

The traditional approach followed for mathematically modeling physico-chemical processes on catalytic surfaces in®ol®es the choice of an infinitesimal surface area on the catalyst and formulation of mass balances in®ol®ing adsorbate surface concentrations. Such a strategy is inadequate when the catalytic surface itself changes dynamically ( with respect to adsorbate-dependent surface arrangement of its catalytic atoms and ) hence its characteristic kinetics. A rigorous mathematical framework to model such () processes is presented. The basic postulates of the theory are the a®ailability of 1 a length scale o®er which the local infinitesimal area is of one surface type of another and () 2 a time scale in which changes in fractional co®erage occurring on the length scale in () 1 are deterministically describable by continuous ®ariables. A combination of probability and area-a®eraging is used to arri®e at a deterministic set of partial differential equations for surface concentrations. The resulting equations include reaction and surface diffusion, and new terms such as dilutionraugmentation of surface concentration of species brought about by phase transformation. Such terms are significant in predicting the nonlinear beha®ior of the system and in extracting the kinetics of surface reactions from dynamic data. An application of the theoretical framework to CO oxidation () on Pt 100 is demonstrated and dilutionraugmentation terms were identified in the purely temporal model. These terms are shown to be significantly important by simulation