Novel Kinetic Model for Heterogeneous Catalysis Based on Free Energy Dissipation via Intermediates Deduced by the Frequency Response Method

Abstract

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” obtainable by a frequency response (FR) technique. The characteristic function to analyze the spectrum derived from the kinetic differential equations contains complex rate constants, (k + iωl)'s; k denotes the ordinary rate constant at an elementary step, l is the novel rate constant due to the free energy dissipation, and ω is the angular frequency scanned in the FR technique. The conclusion has been confirmed 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) ⇄ AX(a) ⇄ BX(a) → Product(s), where X(g) represents propene or hydrogen molecules in the gas phase; AX(a) and BX(a) are the intermediates on the catalysts. This model contains five k's for the three direct and two reverse reactions and two l's of AX and BX for their t...