NOX storage and reduction on a Pt/BaO/alumina monolithic storage catalyst

The performance of a Pt/BaO/Al2O3 washcoated monolith reactor is investigated using propylene as a reductant. The dependence of the time-averaged NOx conversion is reported for several operating parameters, including feed composition, temperature, flow rate, propylene pulse duration and overall cycle time. NOx storage data, which reveal both kinetic and thermodynamic limitations, provide guidance on selecting the feed protocol giving high NOx conversion. Complex nonisothermal transient features spanning the NOx storage and reduction regimes are revealed. Time-averaged NOx conversions exceeding 80% are achieved over a wide range of feed temperatures when short pulses are fed that have a sufficiently high propylene concentration to create fuel-rich conditions. The periodic feed of propylene gives time-averaged NOx conversion significantly exceeding the steady-state conversion for an equivalent propylene feed rate. The results indicate that the rich-lean feed protocol must be tuned in order to achieve a maximum NOx conversion with minimal breakthrough of incompletely oxidized components. The time-averaged conversion achieves a maximum at an intermediate cycle time and reductant pulse duty, with values dependent on the feed temperature and flow rate. The results are compared to previous literature data and interpreted with a phenomenological storage and reduction cycle. (C) 2004 Elsevier B.V. All rights reserved.