The application of combinatorial catalysis tools to the selective catalytic reduction of nitric oxide by propylene in an excess oxygen exhaust

In an effort to improve fuel economy, gasoline engines that operate under excess oxygen conditions have been developed that are up to 25% more efficient than the current designs. However, an appropriate catalyst still remains to be developed in order to commercialize these new engines while meeting exhaust emissions standards for NOx. Such a catalyst would need to perform under conditions that include eliminating >90% of already low NOx concentrations combined with similar levels of hydrocarbons in an excess oxygen atmosphere with a large concentration of water at high space velocities over a wide range of temperatures. The direct decomposition of NO would be desirable but due to a lack of success in this field, research has turned to the selective hydrocarbon reduction (SCR) of NOx with on-board hydrocarbons present in the exhaust stream. However, in spite of decades long research using traditional methods, a catalyst with adequate performance has not been developed yet. Combinatorial catalysis synthesis and analysis tools were developed and applied to this problem.; Over 3000 catalytic formulations, created by impregnating 42 elements from the periodic table onto 5 different porous metal oxide supports (gamma-Al 2O3, CeO2, YSZ, SiO2, TiO2), were synthesized and screened. Mass spectrometry and array channel microreactors were developed and used to screen the catalysts. The experimental conditions were chosen to be similar to an actual lean exhaust environment from a gasoline engine. The catalysts were tested from 100--500°C at a GHSV of 71,600 h-1. The feed gas composition used was: 500ppm NO, 500ppm C3H6, 8% O2, 1400ppm CO, 10% H2O and the balance being helium. The results show that the Pt/TiO2 and Pt/SiO2 binary sets performed the best and Group 3, 4, and 5 transition metals promoted NO conversion on the platinum on silica based catalysts.; A set of experiments was also undertaken to determine the effect of seven different preparation variables on the conversion of nitric oxide and propylene. Platinum on titania catalysts were promoted with zinc or yttrium and preparation variables (such as metal loading and hydrogen reduction) were varied. Major effects on nitric oxide and propylene conversion are platinum loading and calcination temperature.