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This year's Student-Industry Exchange will be held at the ASABE Annual International Meeting in Portland, Ore. on Saturday, July 9, from 5:30 to 6:15 p.m. The Student-Industry Exchange is an [...]

Abstract: In order to study the effect of washcoat composition on lean NO x trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of La-stabilized CeO2 (5wt% La2O3) or CeO2-ZrO2 (Ce:Zr=70:30) were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that aging resulted in deterioration of the NO x storage, NO x release and NO x reduction functions, whereas the observation of lean phase NO2 slip for all of the aged catalysts indicated that LNT performance was not limited by the kinetics of NO oxidation. After aging, all of the catalysts showed increased selectivity to NH3 in the temperature range 250–450°C. TEM, H2 chemisorption, XPS and elemental analysis data revealed two main changes which can explain the degradation in LNT performance. First, residual sulfur in the catalysts, present as BaSO4, decreased catalyst NO x storage capacity. Second, sintering of the precious metals in the washcoat was observed, which can be expected to decrease the rate of NO x reduction. Additionally, sintering is hypothesized to result in segregation of the precious metal and Ba phases, resulting in less efficient NO x spillover from Pt to Ba during NO x adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NO x spillover during catalyst regeneration. Spectacular improvement in LNT durability was observed for catalysts containing CeO2 or CeO2-ZrO2 relative to their non-ceria containing analog. This was attributed to (i) the ability of ceria to participate in NO x storage/reduction as a supplement to the main Ba NO x storage component; (ii) the fact that Pt and CeO2(-ZrO2) are not subject to phase segregation; and (iii) the ability of ceria to trap sulfur, resulting in decreased sulfur accumulation on the Ba component. [Copyright &y& Elsevier]

Abstract: In order to elucidate the effect of washcoat composition on lean NO x trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that in all cases aging resulted in deterioration of the NO x conversion as a consequence of impaired NO x storage and NO x reduction functions, while increased selectivity to NH3 was observed in the temperature range 250–450°C. Elemental analysis, H2 chemisorption and TEM data revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the catalysts, associated with the Ba phase, decreased catalyst NO x storage capacity. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NO x spillover from Pt to Ba during NO x adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NO x spillover during catalyst regeneration. For the aged catalysts, halving the Pt loading from 100 to 50g/ft3 was found to result in a significant decrease in overall NO x conversion, while for catalysts with the same 100g/ft3 Pt loading, increasing the relative amount of Pt on the NO x storage components (BaO and La-stabilized CeO2), as opposed to an Al2O3 support material (where it was co-located with Rh), was found to be beneficial. The effect of Rh loading on aged catalyst performance was found to be marginal within the range studied (10–20g/ft3), as was the effect of BaO loading in the range 30–45g/L. [Copyright &y& Elsevier]