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 proposed as a model reaction to be used for the determination of mass transfer 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 been verified in a small fixed bed facility (average particle diameter 54 mu m), for various reactant concentrations, temperatures and superficial 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 regime (I) at relatively low temperatures, characterized by a reaction order for oxygen of plus one and a carbon monoxide reaction order of minus 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 temperature regime (III) where mass transfer resistances are dominant, and the apparent reaction orders in O-2 and CO are changed to values of zero and plus one, respectively. In case of carbon monoxide oxidation over a platinum catalyst, the observed orders in O-2 and CO provide an extra 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 consequence, the reliability of mass transfer measurements is significantly improved. This has been verified by the application in mass transfer measurements for a packed bed and for a riser system. (C) 1998 Elsevier Science Ltd. All rights reserved.