EFFECT OF LENGTH ON THE PERFORMANCE OF LEAN NOX TRAPS

Abstract

The effect of monolith length on the NOx performance of Lean NOx Traps (LNTs) has been investigated using a bench flow reactor (BFR). The composition of the catalyst samples consists of Pt/K supported on y-Al2O3 washcoat. Samples of 2.22-cm in diameter and three different lengths of 2.54, 5.08 and 7.62 cm were evaluated at a fixed gas hourly space velocity (GHSV) using long and short-cycle experiments with only H2, as the reductant in the rich phase, and the NOx performance was compared between samples of different lengths. No significant difference in performance was observed in long and short cycle experiments with full regeneration. On the other hand, significant difference in performance was observed in short-cycle experiments with partial regeneration: the longer the sample the better the performance. The intra-catalyst concentration of H2 measured by a Spatially Resolved Capillary Inlet Mass Spectrometer (SpaciMS) at different axial locations in short-cycle experiments with partial regeneration indicated that higher H2 consumption in shorter samples is responsible for the reduction of NOx performance.