Enhanced Catalytic Combustion Using Sub-micrometer and Nano-size Platinum Particles

Sub-micrometer and nano-size catalytic particles are significantly more reactive than their bulk counterparts and can be used to enhance the performance of catalytic combustors. Their high specific surface areas (typically 1-200 m(2)/g) and unique morphologies contribute to their enhanced reactivity. Differences in adsorbed species and/or their distributions may also play an important role yet are not clear. The purpose of this study is to quantify the effects of particle size, catalyst loading, and flow residence time on the reactivity of methanol-air premixtures over dispersed platinum (Pt) nanoparticles. As such, experiments were conducted in an atmospheric flow tube reactor seeded with 2-5, 200, and 500 ran Pt particles distributed on a substrate made from deactivated fused silica wool. Temperature measurements and exhaust gas species analyses were obtained for the different size particles, catalyst loadings, and flow conditions. Materials characterization of the particles was also conducted, and scanning electron microscopy (SEM) images were compared before and after sustained reaction to assess changes in their morphology and distribution owed to sintering and/or coalescence of the catalytic particles. Methanol-air premixtures were extremely reactive for a broad range of parameters (light-off at room temperature), consistent with observations at Oak Ridge National Laboratory. Interestingly, the highest steady-state temperatures were measured with 200 and 2-5 nm Pt particles with a small mass loading and 2-5 nm particles with a high mass loading for a fixed flow residence time. The results suggest that the reactivity of methanol-air on Pt increases with a decreasing particle size. Preliminary experiments using ethanol-air vapor premixtures were also conducted and demonstrated enhanced reactivity using catalytic Pt particles.