KINETIC-STUDIES OF DIFFUSION LIMITED GAS SURFACE-REACTIONS BY SPATIALLY RESOLVED GAS SAMPLING - REACTION-RATES AND STICKING COEFFICIENTS IN THE H2 + O2 REACTION ON PT

We demonstrate a new method, based on spatially resolved gas sampling, for studies of a heterogeneous catalytic reaction affected by mass transport in the gas phase. By applying Fick's law to the measured pressure gradients, the net consumption rates of reactants can be calculated. Furthermore, true surface pressures and sticking coefficients can be obtained. To illustrate the potential of this method, we present data from studies at 1 atm total pressure of the H-2 + O2 reaction on Pt. For instance, the true hydrogen/oxygen surface pressure ratio at maximum water production has been determined to 0.1, while a calculation based on nominal background pressures indicates a value around 0.4. At this pressure ratio, the sticking coefficients for hydrogen and oxygen are found to be 5 x 10(-4) and 8 x 10(-5), respectively.