Kinetic studies using temperature-scanning: the oxidation of carbon monoxide

We report on an experimental investigation of carbon monoxide oxidation ove r a 0.05% Pt/g-Al2O3 catalyst using a temperature scanning reactor (TSR) to increase the rate of data acquisition Temperature scanning (TS) allows us to complete an experimental study of the kinetics of this reaction on one c atalyst, at one pressure and feed composition, in less than one working day of fully automated reactor operation. Real-time measurement of CO conversi on was done using a quadruple mass spectrometer (MS). The kinetics of this reaction were quantified by using 12,300 conversion-ra te-temperature (X, r, T) triplets calculated from raw data obtained using o ur TS-PFR, and fitting those with two proposed mechanistic rate equations. Due to the large volume of data and the methods of interpretation used in t emperature scanning, we Will present our results not only in terms of the t raditional curves in the conversion-space time (X,) plane but also introduc e the concept of three-dimensional kinetic surfaces, such as the (X, r, T) surface. The experimental rate data were correlated using two mechanistic rate model s: 1. the Langmuir-Hinshelwood dual site molecular adsorption model (MAM), and 2. the Langmuir-Hinshelwood dual site dissociative adsorption model (DAM), The models differ only in their view of the state of the adsorbed oxygen. T he DAM model, which involves the reaction of oxygen atoms with carbon monox ide molecules, both adsorbed on the same type of site, was found to fit our experimental data over a broader range of reaction conditions and feed com positions. The MAM model, which presumes a reaction of carbon monoxide mole cules with adsorbed molecular oxygen, can fit experimental rates well for i ndividual feed ratios but not over the range of feed ratios used in our stu dy. We therefore, propose that the rate-controlling step in this mechanism consists of a reaction between adsorbed carbon monoxide molecules and adsor bed oxygen atoms. (C) 2000 Elsevier Science B.V. All rights reserved.