PLATINUM-CATALYZED OXIDATION OF CARBON-MONOXIDE AS A MODEL REACTION IN MASS-TRANSFER MEASUREMENTS

The oxidation of CO with oxygen over a Pt/gamma-alumina catalyst is pr oposed as a model reaction to be used for the determination of mass tr ansfer coefficients in packed and fluidized beds. It is applicable at relatively low temperatures (< 800 K) and for very small particles (< 100 mu m). In the present work, the kinetics of this reaction have bee n verified in a small fixed bed facility (average particle diameter 54 mu m), for various reactant concentrations, temperatures and superfic ial gas velocities. As a result, Langmuir-Hinshelwood kinetics (E-a = 75.4 kJ mol(-1)) appeared to describe the experimental results better than a power law expression (E-a = 90.6 kJ mol(-1)). Three temperature regimes can be identified upon interpretation of experimental results with a suitable single particle model: a reaction rate controlled reg ime (I) at relatively low temperatures, characterized by a reaction or der for oxygen of plus one and a carbon monoxide reaction order of min us one, an intermediate temperature interval (regime II) for which the reactions rate is influenced by both mass transfer and kinetics, and where the apparent reaction order in CO and O-2 change to values lower than minus one and higher than one, respectively, and the high temper ature regime (III) where mass transfer resistances are dominant, and t he apparent reaction orders in O-2 and CO are changed to values of zer o and plus one, respectively. In case of carbon monoxide oxidation ove r a platinum catalyst, the observed orders in O-2 and CO provide an ex tra instrument to recognize the prevailing conversion rate controlling phenomenon, apart from known indicators like the observed activation energy value or the influence of hydrodynamic conditions. As a consequ ence, the reliability of mass transfer measurements is significantly i mproved. This has been verified by the application in mass transfer me asurements for a packed bed and for a riser system. (C) 1998 Elsevier Science Ltd. All rights reserved.