Statistically guided high-throughput experimentation of nitrogen oxides storage and reduction catalysts

Statistically guided high-throughput experimentation has been used to study NOx storage and reduction (NSR) catalysts for automotive exhaust applications. NOx storage and reduction catalysts are designed to operate under cyclic fuel lean and fuel rich conditions to effectively reduce NOx under net oxidizing conditions. The catalysts were studied in 16 parallel plug flow reactors connected to a gas phase array that was imaged using FTIR spectroscopic imaging. The resulting data set (collected in less than two seconds) consists of 4096 spatially resolved IR spectra. The gas phase concentrations from each reactor were quantified using either univariate Beer's law type calibrations or multivariate chemometrics calibrations. Factorial and response surface experimental designs were used to study the NSR catalysts as a function of the nitric oxide, oxygen, and reducing agent concentrations, reducing agent composition (carbon monoxide and/or ethylene), temperature, and space velocity, as well as the metal weight loadings of platinum, barium, and iron on gamma-Al2O3. It was found that all the reaction condition variables and the three metal weight loadings affected the NOx storage and nitrous oxide production under fuel lean conditions. The temperature and reducing agent composition were found to be the most significant variables affecting the NOx storage and reduction. It was also found that for a given barium weight loading there existed an optimum platinum weight loading to maximize the NOx storage and reduction. In an additional study, the effect of the total cycle time and the lean fraction of the cycle time were explored. It was found that essentially complete NO x conversion was achieved when the total cycle time was between 60--120 seconds and the lean fraction of that cycle time was below 0.65. The rate limiting step to increasing the lean fraction was found to be the regeneration of the stored NOx during the fuel rich cycle. In summary, multiple NOx storage and reduction catalysts were studied using statistically guided high-throughput experimentation over a wide range of operating conditions and important variables affecting the NOx storage and reduction process were identified.