OH GAS-PHASE CHEMISTRY OUTSIDE A PT CATALYST

Using planar laser induced fluorescence we have measured the ON concen tration profiles outside a Pt catalyst at 1, 5, and 10 torr. The catal yst was heated to 1300 K in a stagnation point flow consisting of 10% hydrogen and 90% oxygen directed onto the surface. The measurements we re compared to a model describing a laminar stagnation point how inclu ding a detailed mechanism with elementary reactions in order to descri be both the gas phase and surface reactions. The simulation shows that the detected OW was not produced by gas phase reactions. Instead it i s formed on the surface by H + O recombination, and a small percentage of it desorbs and diffuses out from the catalyst. At 1 torr the form of the ON gradient outside the catalyst was found to be determined sol ely by diffusion and convection. At 5 and 10 torr gas phase reactions also had to be included to correctly describe the shape of the OH conc entration gradient. The dominant gas phase reaction is removal of OH m olecules through reaction with hydrogen. (C) 1998 Academic Press.