NOx storage and reduction with H2 on Pt/BaO/Al2O3 monolith: Spatio-temporal resolution of product distribution

  • Clayton R
  • Harold M
  • Balakotaiah V
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Abstract

The regeneration of a model Pt/BaO/Al2O3monolith catalyst was studied with hydrogen as the reductant to elucidate the reaction pathways to molecular nitrogen and ammonia. NOxstorage and reduction experiments (NSR) were conducted with a 2 cm length monolith for a wide range of feed conditions. The NSR experiments were replicated for a series of monoliths of progressively decreasing length, enabling the construction of spatio-temporal profiles of reactant and product concentrations. The results show that there are two primary competing routes to the desired N2product; specifically a direct route from the reduction of stored NOxby H2(H2+ NOx→ N2) or by a sequential route through NH3(H2+ NOx→ NH3; NH3+ NOx→ N2). A comparison between H2and NH3as reductant feeds during NSR revealed H2is a more effective reductant in terms of NOxconversion for temperatures below approximately 230 °C. At higher temperatures (230-380 °C), the regeneration of stored NOxis feed-limited and the difference between the reductants H2and NH3is found to be small with H2being a slightly superior reductant. Experimental measurements of the traveling front velocity are compared with a simple feed-limited model that assumes complete consumption of H2as stored NOxis depleted. At lower temperatures the regeneration is limited by chemical processes at the Pt/Ba interface. The findings are pieced together to establish a phenomenological description of the spatio-temporal features of the lean NOxtrap with hydrogen as the reductant. © 2008 Elsevier B.V. All rights reserved.

Author-supplied keywords

  • Barium
  • Hydrogen
  • Lean NOxtrap
  • NOx
  • NOxstorage and reduction
  • Platinum
  • Selective catalytic reduction

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