Performance of NOx storage–reduction catalyst in the temperature–reductant concentration domain by response surface methodology

The performance trends of a homemade Pt–Ba/Al2O3 monolith catalyst for NOx storage and reduction at different temperatures and varying the hydrogen concentration fed during the regeneration period have been found by the response surface methodology. NOx trapping efficiency during the lean period, selectivity to N2/N2O/NH3 and global NSR efficiency have been used as the response for describing the performance of the monolith. Maximum NOx trapping efficiency (80%) was found when operating at relative low temperature (240 °C) and high reductant concentration (>2% H2) but with limited selectivity to N2, whereas maximum selectivity to N2 (above 90%) was achieved at high temperature (>300 °C) and hydrogen in defect (<1%) but with limited NOx trapping efficiency. As both response should be as high as possible for NSR commercial systems, they are combined in the global NSR efficiency or production of N2 related to NO in the feedstream (vol.%). Maximum NSR efficiency (65%) was achieved at 270 °C and 1% H2, with NOx trapping efficiency of 77% and N2 selectivity of 85%. It has been verified the consistency of data obtained with mechanistic aspects already reported in the literature. The role of ammonia as an intermediate that reacts with NOx stored has been confirmed and also the primary routes of H2 which reacts with stored NOx and the sequential route of stored NOx reacting with H2 and then NH3 reducing with stored NOx downstream. N2/NH3/N2O distribution at the reactor exit depends on the extent of each route in the reaction network and is a complex function of temperature, gas phase and surface compositions.