High-Temperature Heterogeneous Redox Catalysis for NOx Abatement

摘要

This Phase I SBIR program was directed towards the synthesis, characterization,and determination of preferred catalyst compositions for the high-temperature direct (reagentless) decomposition of nitrogen oxides in exhaust streams. Phase I results showed clearly that significant persistent (nontransient) activity (35% removal) for direct deNO(x) (at > 500 deg C) could be attained in helium at space velocities of 1,000,000 per h (3.6ms residence time) over a brownmillerite catalyst supported on a powdered ceramic (yttria-stabilized zirconia) representative of thermal barrier coatings, in the presence of 16% O2, absent of any reagent. This catalyst, when unsupported, showed persistent activity (27% removal at 500,000 per h for at least 6 hours and at least 140 hours at 50,000 per h). Significant activity was measured at up to 1,000 deg C. These catalysts also possessed exceptional activity for the combustion of propane and propylene as well as measurable activity for oxidation of CO. Preliminary results showed tolerance to feedstream CO2 (10%) and SO2 (10ppm). Results point clearly to probable attainment of Air Force's Phase II targets of 50% removal in millisecond residence time regimes and retention of 50% of initial activity after 500 hours.