Effect of ammonia treatment on PT catalyst used for low-temperature reaction

Platinum based catalysts are well known as the most active ones among noble metals for oxidation of hydrocarbons as well as hydrogen. Microcombustion experiments using bare Pt foil catalyst have shown that hydrocarbon fuels (e.g. propane) can be oxidized at low-temperature (< 60°C) and ignited (<90°C) by treating the catalyst surface by burning propane-air mixtures with ∼ 5% of the propane replaced by ammonia for half an hour. This NH3 pre-treatment etches the catalyst surface and creates surface structures on the scale of few urns, completely unlike those without NH3 treatment. This change in structure with NH3 treatment is noteworthy in that it increases the performance of the catalyst by a factor of 3, but only for low Re, corresponding to conditions with low maximum reaction temperatures characteristic of microcombustors. However, no similar such low-temperatures were found without NH3 pre-treatment, even for catalytic reactions. This is not merely a surface area effect, since increasing bulk catalyst area had almost no effect on combustion performance. Nevertheless, it may be possible to further extend reaction and ignition to even lower temperatures by examining alternative hydrocarbon fuels and catalysts. Self-starting fuels and catalysts are highly desirable, especially for the micro-combustors used for MEMS (Micro Electro-Mechanical Systems) power generators, because it would eliminate the need for glow plugs, supplemental battery, electronics, etc. associated with active ignition systems.