NOVEL KINETIC-MODEL FOR HETEROGENEOUS CATALYSIS BASED ON FREE-ENERGY DISSIPATION VIA INTERMEDIATES DEDUCED BY THE FREQUENCY-RESPONSE METHOD

A novel kinetic model for heterogeneous catalysis based on the flow of free energy (instead of ordinary mass-flow) is proposed; the chemical kinetic model is valid to interpret a ''reaction-rate spectrum'' obta inable by a frequency response (FR) technique. The characteristic func tion to analyze the spectrum derived from the kinetic differential equ ations contains complex rate constants, (k + i omega l)'s; k denotes t he ordinary rate constant at an elementary step, l is the novel rate c onstant due to the free energy dissipation, and omega is the angular f requency scanned in the FR technique. The conclusion has been confirme d by actual data obtained in a catalytic hydrogenation of propene over Pt and/or Rh metals on the basis of a three-stage model: X(g) reversi ble arrow A(X)(a) reversible arrow B-X(a) --> Product(s), where X(g) r epresents propene or hydrogen molecules in the gas phase; A(X)(a) and B-X(a) are the intermediates on the catalysts. This model contains fiv e k's for the three direct and two reverse reactions and two l's of A( X) and B-X for their two direct reactions. On the basis of the present results, a generic procedure to analyze a reaction-rate spectrum is p roposed.