Influence of site energy distribution on catalytic rates with multicomponent chemisorption

Abstract

Without using the assumption of constancy of mole fractions in adsorption space, dual-component adsorption accompanied by catalytic reaction on a heterogeneous surface is modeled. A simple parallel reaction scheme which is supposed to idelalize key steps in cracking and disproportionation reactions is studied. Quantities of interest in catalytic kinetics such as mean surface coverage, mean squared surface coverage, and others are calculated as statistical averages over the bivariate analogs of four well-known monovariate distributions, with the assumption of relaistic heats of adsorption. Using a variant of the Mellin transform method proposed earlier, explicit expressions for the rates are given as functions of partial pressure ratio and the parameters characterizing the site energy distribution. Methods are proposed to determine the characteristic ratio of partial pressures at which a desired selectivity pattern is realized. Lastly, two reaction schemes which outline key steps in platforming and reforming reactions and which occur on bifunctional catalysts are analyzed and methods for determining the characteristic pressure ratio are suggested.