Frequency Response Study of the Dynamics of the Platinum Catalyzed Interconversion of Methylcyclohexane, Toluene, and Hydrogen near Equilibrium

• Published in: The journal of physical chemistry. B 2005-02, Vol.109 (6), p.2421-2431
• Main Authors: Reyes, Sebastián C, Sinfelt, John H, DeMartin, Gregory J
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp048708d

The dynamics of the platinum catalyzed interconversion of methylcyclohexane, toluene, and hydrogen near equilibrium were investigated in a closed reactor system by a frequency response method at temperatures in the range of 433 to 473 K and at total pressures in the vicinity of 80 to 110 Torr. The gas phase in contact with the platinum catalyst was always hydrogen-rich, with hydrogen to hydrocarbon mole ratios maintained in the range of 3.2 to 4.6. The frequency response method utilized small perturbations (lower than 1%) of the volume of the system, with measurements of the total pressure being used to determine the response of the system. The range of perturbation frequencies investigated was approximately 0.002 to 3 Hz (0.013 to 19 rad s-1). The experiments revealed two characteristic relaxation frequencies that are associated with the dynamics of the interconversion. The dynamics of the system are interpreted in terms of a simple two-step interconversion sequence with the aid of a phenomenological frequency response theory formulated in terms of relaxation frequencies of the steps and equilibrium properties of the system. It is concluded that one of the steps, a toluene adsorption−desorption step, is much slower than the other, a step involving the interconversion of the gas-phase methylcyclohexane and chemisorbed toluene that releases or consumes hydrogen in the process.