OH Gas Phase Chemistry outside a Pt Catalyst

Abstract

Using planar laser induced fluorescence we have measured the OH concentration profiles outside a Pt catalyst at 1, 5, and 10 torr. The catalyst was heated to 1300 K in a stagnation point flow consisting of 10% hydrogen and 90% oxygen directed onto the surface. The measurements were compared to a model describing a laminar stagnation point flow including a detailed mechanism with elementary reactions in order to describe both the gas phase and surface reactions. The simulation shows that the detected OH was not produced by gas phase reactions. Instead it is 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 OH gradient outside the catalyst was found to be determined solely 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 concentration gradient. The dominant gas phase reaction is removal of OH molecules through reaction with hydrogen.