Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Mechanical Engineering

Major Professor

Ke Nguyen

Committee Members

Stuart Daw, J. Roger Parsons, David K. Irick


The effect of monolith length on the NOx performance of two different Lean NOx Traps has been investigated using a bench flow reactor (BFR). The washcoat composition of one of the catalysts consists of Pt/K/γ-Al2O3; the major components of the other catalyst include Pt, Pd, Rh, barium, ceria and zirconia supported on γ-alumina washcoat. Samples of 2.22-cm in diameter and length of 2.54, 5.08 and 7.62-cm within each LNT were evaluated with long and short-cycle experiments at a fixed gas hourly space velocity, and results were compared between samples of different lengths. No significant difference in performance was observed in long and short-cycle experiments with full regeneration. On a contrary, significant difference was observed in short-cycle experiments with partial regeneration: the longer the sample the better the performance.

The intra-catalyst concentration of H2 measured at different axial locations in short-cycle experiments indicated higher H2 consumption in shorter samples. A series of experiments was carried out to ascertain different mechanisms of H2 consumption, and results indicated different degrees of lean and rich front back-mixing for samples of different sizes. Higher back-mixing in shorter samples resulted in a higher H2 loss via its oxidation by O2 and lesser H2 availability for reducing stored NOx, which in turn affected catalyst’s performance when regeneration was limited by amount of H2 available.

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