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

We report on an experimental investigation of carbon monoxide oxidation over a 0.05% Pt/γ-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 catalyst, at one pressure and feed composition, in less than one working day of fully automated reactor operation. Real-time measurement of CO conversion was done using a quadruple mass spectrometer (MS). The kinetics of this reaction were quantified by using ∼12,300 conversion–rate–temperature (X, r, T) triplets calculated from raw data obtained using our 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 temperature scanning, we will present our results not only in terms of the traditional curves in the conversion–space time (X, τ) plane but also nitroduce the concept of three-dimensional kinetic surfaces, such as the (X, r, T) surface. The experimental rate data were correlated using two mechanistic rate models: 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. The DAM model, which involves the reaction of oxygen atoms with carbon monoxide 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 compositions. The MAM model, which presumes a reaction of carbon monoxide molecules with adsorbed molecular oxygen, can fit experimental rates well for individual feed ratios but not over the range of feed ratios used in our study. We therefore, propose that the rate-controlling step in this mechanism consists of a reaction between adsorbed carbon monoxide molecules and adsorbed oxygen atoms