The turnover frequency of methylcyclohexane dehydrogenation to toluene on a Pt reforming catalyst

Abstract The dehydrogenation of methylcyclohexane to toluene is representative of one of the major types of reactions occurring in the catalytic reforming of petroleum naphtha fractions. An investigation of the kinetics of the reaction on a platinum reforming catalyst in the temperature range of 588–645 K was reported by the writer and coworkers in 1960. Included in that paper was a value of the reaction rate per unit surface area of platinum at 588 K, along with a rate expression permitting one to obtain such information over a range of reaction conditions. The determination of this intrinsic measure of the dehydrogenation activity of the 1 nm clusters of platinum in the catalyst was made possible by the work of Spenadel and Boudart on the development of a hydrogen chemisorption method for the evaluation of the platinum surface area. In the present paper, the writer reports the dehydrogenation activity of the platinum clusters in the form of a turnover frequency, a measure of catalytic activity advocated by Boudart analogous to that used by workers in enzyme catalysis. The writer then extrapolates the rate equation in the 1960 paper of Sinfelt and coworkers to determine a turnover frequency at a substantially higher temperature characteristic of a catalytic reforming operation, and compares this with a value at that temperature determined directly by experiment. Finally, the turnover frequency for methylcyclohexane is compared with that for its homolog cyclohexane.