Homogeneous-heterogeneous oxidation reactions over platinum and inert surfaces

The coupled homogeneous-heterogeneous oxidation of premixed hydrogen/air mixtures over platinum and inert surfaces is modeled in a stagnation-point flow reactor using detailed surface kinetics, gas-phase kinetics, and transport phenomena. Ignitions and extinctions are determined using numerical bifurcation theory, and simulation results are compared with experimental data. It is shown that the homogeneous ignition is inhibited by catalytic formation of H2O and can be affected by multicomponent transport phenomena. In addition, adsorption of hydrogen atoms to the surface can also influence homogeneous ignition. Cleaner combustion with low concentrations of unburned fuel and NOx species is achieved when Pt is used compared to inert surfaces. It is shown that these low concentrations of fuel near the surface are caused by synergetic gas-phase and surface chemistry effects.