Performance of NO x storage–reduction catalyst in the temperature–reductant concentration domain by response surface methodology

Abstract

The performance trends of a homemade Pt–Ba/Al 2O 3 monolith catalyst for NO x storage and reduction at different temperatures and varying the hydrogen concentration fed during the regeneration period have been found by the response surface methodology. NO x trapping efficiency during the lean period, selectivity to N 2/N 2O/NH 3 and global NSR efficiency have been used as the response for describing the performance of the monolith. Maximum NO x trapping efficiency (80%) was found when operating at relative low temperature (240 °C) and high reductant concentration (>2% H 2) but with limited selectivity to N 2, whereas maximum selectivity to N 2 (above 90%) was achieved at high temperature (>300 °C) and hydrogen in defect (<1%) but with limited NO x 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 N 2 related to NO in the feedstream (vol.%). Maximum NSR efficiency (65%) was achieved at 270 °C and 1% H 2, with NO x trapping efficiency of 77% and N 2 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 NO x stored has been confirmed and also the primary routes of H 2 which reacts with stored NO x and the sequential route of stored NO x reacting with H 2 and then NH 3 reducing with stored NO x downstream. N 2/NH 3/N 2O 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.