Effects of hydrogen addition on the catalytic oxidation of carbon monoxide over platinum at power generation relevant temperatures

Abstract

The catalytic oxidation of CO and CO/H2 fuel mixtures over platinum was investigated experimentally and numerically at fuel-lean stoichiometries, pressure of 5bar and a surface temperature range relevant for large-turbine and micro-turbine based power generation systems (600–800K). Experiments were performed in an optically accessible catalytic channel flow reactor with the application of in situ, spatially resolved 1-D Raman measurements of gas-phase species concentrations across the reactor boundary layer in order to determine the catalytic reactivity, and planar OH-LIF for monitoring the potential onset of homogeneous ignition. Numerical simulations were carried out with a 2-D elliptic CFD code in conjunction with a detailed heterogeneous kinetic scheme and transport. The reaction scheme, constructed by implementing recent updates to an existing kinetic model, reproduced the Raman-measured species profiles of either pure CO or combined CO/H2 fuels under all examined conditions. The addition of hydrogen promoted kinetically the oxidation of CO at wall temperatures as low as 610K, whereby the catalytic reactions of H2 were fully lit and the CO conversion was mixed transport/kinetically controlled. This low temperature limit was of prime interest to idling operation for large gas turbines and to normal operation for recuperative microturbine systems. Moreover, kinetic analysis suggested that the promoting impact of H2 addition on CO oxidation was due to indirect influence of hydrogen reactions on the surface species coverage, whereas direct coupling steps between CO and H2 were of minor importance. Finally, simulations indicated that for wall temperatures less than 520K, which were well-below the minimum reactant inlet temperatures in power generation systems, the added H2 inhibited the oxidation of CO.